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UNIT 3—THE BIG BANG

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UNIT 3—STARS & ELEMENTS TEXT READER 1 A Little Big History of Silver

Taking a closer look at the popular precious metal.

A Little Big History of Silver (1110L) By Big History Project It’s amazing how much you can learn when you look at things through the lens of Big History. Take a medium-weight element like silver, a shiny whitish metal with an unassuming spot (atomic number 47) on the periodic table between palladium and cadmium. The value of silver Silver puts the luster in jewelry, helps our cell phones and MP3 players work better, and even makes hospitals safer. Let’s explore the many roles that silver has played throughout history. What makes silver more valuable to us than other minerals? Its beauty is one thing. This attractive and reflective metal has fascinated men and women for a long time. Silver also is fairly scarce — and things that are both beautiful and rare tend to be worth a lot; think of diamonds, gold, and masterpieces of art. Silver is very durable, too. And it’s malleable, meaning it’s easy to shape. All these qualities have made silver very useful and valuable to this day. Silver’s monetary value has long been appreciated. Thought to be perhaps the oldest coin, the “Lydian Lion” was minted in modern-day Turkey about 2,700 years ago; early metalworkers — chemists of sorts — made the coins from electrum, an alloy of gold and silver. The Minoan civilization, which flourished on the island of Crete around 2000 BCE, and the Mycenaean people of early mainland Greece imported great amounts of silver that were mined in ancient Armenia. Transport of the metal between all of these places helped to accelerate trade throughout the Mediterranean region. After the catastrophic destruction of the Minoan civilization in 1600 BCE, and the decline of the Mycenaean culture around 1200 BCE, silver’s prominence continued as production shifted with the rising civilization of classical Greece. The silver mines of Laurium, near Athens, paid for the Italian lumber used to build the fleets of triremes, warships with three levels of rowers, that made ancient Athens a naval superpower. The Romans would later adopt silver as one of their main currencies as well. Silver helped advance global civilization by connecting East and West through trade. Silver was scarce in China, but nonetheless much valued as currency. So, during the Middle Ages, Europeans used silver to buy Chinese goods — gunpowder, tea, ceramics, and silk — which were then carried over the fabled Silk Road. Later, when the Spanish discovered silver mines

UNIT 3—STARS & ELEMENTS TEXT READER 2 in Mexico and Peru, they established a sailing route across the Pacific, trading South American silver, some of it plundered, for Chinese silk. Silk was desirable because it made light and cool clothing much in demand by Spanish settlers in the hot, humid climate in parts of Mexico, Central America, and South America. As we’ll see elsewhere in this course, when goods get traded, so do ideas. So silver played a role in advancing collective learning. By the seventeenth century, Mexican “pieces of eight” — also known as “Spanish dollars” — had become the world’s first global currency. The U.S. dollar was based on these coins and for a long time many U.S. coins contained silver. The Latin word for silver is argentum. What South American country sounds like that? Right — Argentina! During the time of the Spanish explorers in the 1500s, Argentina was thought to be rich in what shiny metal element? Silver, of course. The many uses of silver Silver also has strong antibacterial properties that have been acknowledged for millennia. The ancient Greek physician Hippocrates, sometimes called the “father of medicine,” wrote of silver’s healing properties. Early records indicate that the Phoenicians used silver vessels to keep water, wine, and vinegar pure during their long voyages at sea. You may have heard the phrase “born with a silver spoon in your mouth.” That’s not necessarily about being rich. In the eighteenth century, babies fed with silver spoons were thought to be healthier than those fed with spoons made from wood or other materials. Today, many hospitals fight infections with equipment that is embedded with silver. The metal is even used in the thread of some socks. Why? The silver kills bacteria that make the socks smell bad! Silver is the best metallic conductor of electricity, better than copper or gold. That’s why so many electronics, like your computer keyboard or music player, rely on it. Alloys of silver are used in dentistry, photography, even in the operation of nuclear power plants. Silver also helps keep airplanes aloft. Because of its poor coefficient of friction (meaning, it’s slippery!), silver is used to coat the ball bearings used in jet engines. But did you know that billions of years ago there was no silver anywhere in the Universe? So where did it come from? Like most other elements in the periodic table, silver was created in dying stars — and in the cataclysmic supernova explosions that sometimes marked their final demise. This is the only place where temperatures get hot enough to fuse hydrogen nuclei together to form larger atoms. These larger, heavier atoms eventually went on to help form planets like Earth. So in a sense, silver, like everything else around you, was made from the first atoms of hydrogen. Where and when was hydrogen created? In the Big Bang itself. It turns out silver has a pretty big history!

A Little Big History of Silver (1010L) By Big History Project, adapted by Newsela

UNIT 3—STARS & ELEMENTS TEXT READER 3 It’s amazing how much you can learn when you look at things through the lens of Big History. Take an element like silver. You may just think of it as a shiny metal used to make jewelry. Its spot (atomic number 47) on the periodic table between palladium and cadmium may not seem meaningful. But, silver is of great importance to science. The value of silver Silver isn't just for rings, earrings and chains. It also helps our cell phones and TVs work better, and even makes hospitals safer. Let’s explore the many roles that silver has played over thousands of years. What makes silver more valuable to us than other minerals? Its beauty is one thing. Like most shiny substances, it has fascinated men and women throughout history. Silver also is fairly scarce — and things that are both beautiful and rare tend to be worth a lot; think of diamonds, gold, and masterpieces of art. Silver is very durable, too. And it’s malleable, meaning it’s easy to shape. All these qualities have made silver useful and valuable to this day. Silver has been used as money throughout history. Thought to be perhaps the oldest coin, the “Lydian Lion” was minted in modern-day Turkey about 2,700 years ago. Early metalworkers — chemists of sorts — made the coins from electrum. That metal was an alloy (a mix of metals) of gold and silver. The Minoan civilization, which flourished on the island of Crete around 2000 BCE, and the Mycenaean people of early Greece imported great amounts of silver that were mined in ancient Armenia. The transport of the metal between all of these places helped to speed up trade throughout the Mediterranean region. The Minoan civilization was catastrophically destroyed in 1600 BCE, and Mycenaean culture declined around 1200 BCE. Yet, silver’s prominence continued as production shifted with the rising civilization of classical Greece. Silver mines near Athens paid for the Italian lumber used to build the fleets of warships that made ancient Athens a naval superpower. The Romans would later adopt silver as one of their main currencies as well. Silver helped advance global civilization by connecting East and West through trade. Silver was scarce in China, but nonetheless much valued as currency. So, during the Middle Ages, Europeans used silver to buy Chinese goods — gunpowder, tea, ceramics, and silk — which were then carried over the fabled Silk Road, a 4,000-mile trade route connecting China to Europe. Later, when the Spanish discovered silver mines in Mexico and Peru, they established a sailing route across the Pacific. They traded South American silver — some of it plundered — for Chinese silk. Silk was highly desirable. It made light and cool clothing much in demand by Spanish settlers in the hot, humid climate in parts of Mexico, Central America, and South America. As we’ll see elsewhere in this course, when goods get traded, so do ideas. So silver played a role in advancing the collective learning of humankind.

UNIT 3—STARS & ELEMENTS TEXT READER 4 By the seventeenth century, Mexican “pieces of eight” — also known as “Spanish dollars” — had become the world’s first global currency. The U.S. dollar was based on these coins. For a long time, many U.S. coins contained silver. The Latin word for silver is argentum. What South American country sounds like that? Right — Argentina! During the time of the Spanish explorers in the 1500s, Argentina was thought to be rich in what shiny metal element? Silver, of course. The many uses of silver Silver also has strong antibacterial properties to ward off bacteria that can cause infections. This has been known for thousands of years. The ancient Greek physician Hippocrates, sometimes called the “father of medicine,” wrote of silver’s healing properties. Early records indicate that the Phoenicians used silver vessels to keep water, wine, and vinegar pure during their long voyages at sea. You may have heard the phrase “born with a silver spoon in your mouth.” That’s not necessarily about being rich. In the eighteenth century, babies fed with silver spoons were thought to be healthier than those fed with spoons made from wood or other materials. Today, many hospitals fight infections with equipment that is embedded with silver. Silver is even used in the thread of some socks. Why? The silver kills bacteria that make the socks smell bad! Silver is the best metallic conductor of electricity, better than copper or gold. That’s why so many electronics, like your computer keyboard or music player, rely on it. Alloys of silver are used in dentistry, photography, even in the operation of nuclear power plants. Silver also helps keep airplanes aloft. Because it creates little friction (meaning, it’s slippery!), silver is used to coat the ball bearings used in jet engines. But did you know that billions of years ago there was no silver anywhere in the Universe? So where did it come from? Like most other elements in the periodic table, silver was created in dying stars — and in the cataclysmic supernova explosions that sometimes marked their final dying stage. This is the only place where temperatures get hot enough to fuse hydrogen nuclei together to form larger atoms. These larger, heavier atoms eventually went on to help form planets like Earth. So in a sense, silver, like everything else around you, was made from the first atoms of hydrogen. Where and when was hydrogen created? In the Big Bang itself. It turns out silver has a pretty big history!

A Little Big History of Silver (880L) By Big History Project, adapted by Newsela It’s amazing how much you can learn when you look at things through the lens of Big History. Take an element like silver. The shiny metal may not seem important from a

UNIT 3—STARS & ELEMENTS TEXT READER 5 scientific standpoint. It's just atomic number 47 on the periodic table, sandwiched between palladium and cadmium. But it's played a vital role in science and trade for thousands of years. The value of silver You've seen silver in plenty of jewelry and utensils. But, it also helps our cell phones and TVs work better, and even makes hospitals safer. Let’s explore silver's significance throughout history. What makes silver more valuable to us than other minerals? Its beauty is one thing. Like most shiny substances, silver has fascinated men and women. Silver also is fairly scarce — and things that are both beautiful and rare tend to be worth a lot; think of diamonds, gold, and masterpieces of art. Silver is very durable, too. And it’s malleable, meaning it’s easy to shape. All these qualities have made silver very useful and valuable to this day. Silver has long been used as money. Perhaps the oldest coin was minted in modern-day Turkey about 2,700 years ago. Early metalworkers — chemists of sorts — made the coins from electrum. It was an alloy (a mixture of metals) of gold and silver. Early Greek civilizations bought silver from Armenia. The transport of the metal between these places helped to grow trade throughout the Mediterranean region. Silver’s importance continued as Greek civilization rose. Silver mines near the Greek city of Athens paid for Italian lumber used to build its warships. Fleets of those warships helped turn that ancient city-state into a naval superpower. The Romans would later choose silver as one of their main currencies as well. Silver helped advance global civilization by connecting East and West through trade. Silver was scarce in China. Nonetheless, it was much valued as currency. So, during the Middle Ages, Europeans used silver to buy Chinese goods — gunpowder, tea, ceramics, and silk. Then they carried over the fabled Silk Road, a 4,000-mile route connecting China to Europe. Later, the Spanish discovered silver mines in Mexico and Peru. To move the silver — some which they stole — the Spanish established a sailing route across the Pacific. They traded South American silver for Chinese silk. Silk was highly desirable. It made light and cool clothing. Spanish settlers in the hot, humid climate in parts of Mexico, Central America, and South America treasured it. As we’ll see elsewhere in this course, when goods get traded, so do ideas. So silver helped advance the collective learning of humankind. By the seventeenth century, Mexican “pieces of eight” — also known as “Spanish dollars” — had become the world’s first global currency. The U.S. dollar was based on these coins. For a long time, many U.S. coins contained silver.

UNIT 3—STARS & ELEMENTS TEXT READER 6 The Latin word for silver is argentum. What South American country sounds like that? Right — Argentina! During the time of the Spanish explorers in the 1500s, Argentina was thought to be rich in what shiny metal element? Silver, of course. The many uses of silver Silver also has antibacterial properties that fight off bacteria that cause harmful infections. Early scientists discovered this thousands of years ago. The ancient Greek physician Hippocrates, sometimes called the “father of medicine,” wrote of silver’s healing properties. Early records indicate that the Phoenicians used silver vessels to keep water, wine, and vinegar pure during their long voyages at sea. You may have heard the phrase “born with a silver spoon in your mouth.” That’s not necessarily about being rich. In the eighteenth century, babies fed with silver spoons were thought to be healthier than those fed with spoons made from wood or other materials. Today, many hospitals fight infections with equipment containing silver. Silver is even used in the thread of some socks. Why? The silver kills bacteria that make the socks smell bad! Silver is the best metallic conductor of electricity. It's better than copper — which is used in most electrical wires — or gold. That’s why so many electronics, like your computer keyboard or music player, rely on it. Alloys of silver are used in dentistry, photography, even in the operation of nuclear power plants. Silver also helps keep airplanes aloft. Silver creates little friction (meaning, it’s slippery!). Because of that, silver is used to coat the ball bearings used in jet engines. But did you know that billions of years ago there was no silver anywhere in the Universe? So where did it come from? Like most other elements, silver was created in dying stars. As stars die they can explode in a giant flash of light called a supernova. A single supernova can create more energy than our Sun will in its entire life. Supernovas create most of the heavy elements in our Universe. Their explosions create temperatures hot enough to fuse hydrogen nuclei together to form larger atoms. These larger, heavier atoms helped form planets like Earth. So in a sense, silver, like everything else around you, was made from the first atoms of hydrogen. Where and when was hydrogen created? In the Big Bang itself. It turns out silver has a pretty big history!

A Little Big History of Silver (770L) By Big History Project, adapted by Newsela It’s amazing how much you can learn when you look at things through the lens of Big History. Take an element like silver. You may just think of it as a shiny metal used to make jewelry. But, it's of great importance to science.

UNIT 3—STARS & ELEMENTS TEXT READER 7 The value of silver Silver is widely used in technology and medicine. It helps our cell phones and TVs work better. It even makes hospitals safer. Let’s explore the many roles that silver has played throughout history. What makes silver more valuable to us than other minerals? Its beauty is one thing. The shiny metal has fascinated men and women for ages. Silver also is fairly scarce. Things that are both beautiful and rare tend to be worth a lot — think of diamonds and gold. Silver is a durable metal that lasts for ages, too. And it’s malleable, meaning it’s easy to shape. All these qualities have made silver very useful and valuable to this day. Silver was one of the earliest forms of money. Perhaps the oldest coin was minted in modern- day Turkey about 2,700 years ago. Early metalworkers made the coins from electrum. It was an alloy (a mixture of metals) of gold and silver. Early Greek civilizations bought silver from Armenia. Transporting the metal helped grow trade throughout the Mediterranean region. Silver’s importance continued as Greek civilization rose. Silver mines near the Greek city of Athens paid for the Italian lumber it bought. Athens used the lumber to build the warships that made it a naval superpower of the ancient world. The Romans would later use silver as money as well. Silver even helped advance global civilization. It connected East and West through trade. Silver was scarce in China. Nonetheless, it was much valued as currency. So, during the Middle Ages, Europeans used silver to buy Chinese goods such as gunpowder, tea, and silk. Then they carried the goods over the fabled Silk Road, a 4,000-mile road connecting China to Europe. Later, the Spanish discovered silver mines in Mexico and Peru. To move the silver, they established a sailing route across the Pacific. They traded South American silver — some of it stolen — for Chinese silk. Silk was incredibly desirable. Light and cool clothing could be woven from it. Spanish settlers in the hot, wet climates of Mexico, Central America, and South America wanted it very much. As we’ll see elsewhere in this course, when goods get traded, so do ideas. The spread of silver helped spread learning throughout the world. This increased humankind's collective learning. By the seventeenth century, Mexican “pieces of eight” had become the world’s first global money, or currency. The U.S. dollar was based on these coins. For a long time, many U.S. coins contained silver. The Latin word for silver is argentum. What South American country sounds like that? Right — Argentina! During the time of the Spanish explorers in the 1500s, Argentina was thought to be rich in what shiny metal element? Silver, of course.

UNIT 3—STARS & ELEMENTS TEXT READER 8 The many uses of silver Silver also has strong powers to fight bacteria that can cause infections. Scientists first discovered this thousands of years ago. The ancient Greek doctor Hippocrates is sometimes called the “father of medicine." He wrote of silver’s healing properties. Early records indicate that the Phoenicians used silver containers to keep water, wine, and vinegar pure during long voyages at sea. You may have heard the phrase “born with a silver spoon in your mouth.” That’s not necessarily about being rich. In the eighteenth century, babies fed with silver spoons were thought to be healthier than those fed with spoons made from wood. Today, many hospitals fight infections with equipment that contains silver. Silver is even used in the thread of some socks. Why? The silver kills bacteria that make the socks smell bad! Silver is the best metallic conductor of electricity. It's better than copper, which is used in most electrical wires. It's even better than gold. That’s why so many electronics, like your computer keyboard, rely on it. Alloys of silver are used in dentistry and photography. Even nuclear power plants use silver to operate. Silver also helps keep planes in the air. Silver creates little friction (meaning, it’s slippery!). Because of that, silver is used to coat the ball bearings used in jet engines. But did you know that billions of years ago there was no silver anywhere in the Universe? So where did it come from? Like most other elements, silver was created in dying stars. As stars die they can explode in a giant flash of light called a supernova. A single supernova can create more energy than our Sun does in its entire life. Supernovas create most of the heavy elements in our Universe. Their explosions create temperatures hot enough to fuse hydrogen nuclei together to form larger atoms. These larger, heavier atoms helped form planets like Earth. So in a sense, silver, like everything else around you, was made from the first atoms of hydrogen. Where and when was hydrogen created? In the Big Bang itself. It turns out silver has a pretty big history!

UNIT 3—STARS & ELEMENTS TEXT READER 9 Dmitri Mendeleev: Building the Periodic Table of Elements

Biography of the Russian chemist and teacher who devised the periodic table — a comprehensive system for classifying the chemical elements.

Dmitri Mendeleev: Building the Periodic Table of Elements (1110L) By Michelle Feder Dmitri Mendeleev, a Russian chemist and teacher, devised the periodic table — a comprehensive system for classifying the chemical elements. Organizing matter In the mid-1700s, chemists began actively identifying elements, which are substances made up of just one kind of atom. But a century later, they still used a variety of symbols and acronyms to represent the different materials — there just wasn’t a common lexicon. In 1869, the Russian chemist Dmitri Mendeleev came to prominence with his tabular diagram of known elements. This basic ingredient list, of which all matter exists, became known as the periodic table. Here’s what’s especially amazing: Mendeleev’s chart allotted spaces for elements that were yet to be discovered. For some of these missing pieces, he predicted what their atomic masses and other chemical properties would be. When scientists later discovered the elements Mendeleev had expected, the world got a glimpse of the brilliance behind the periodic table. A difficult childhood Mendeleev was born in 1834 in the far west of Russia’s Siberia, the youngest of a dozen or more children (reports vary). His family faced one crisis after another. When Dmitri was little, his father, a teacher, went blind, and his mother went to work. She became the manager of a successful glass factory. Tragedy struck again in 1848, when the factory burned down, and the family faced poverty. Mendeleev’s mother was determined to get him an education, and traveled with him a great distance, to Moscow and then to St. Petersburg, to do so. Ten days after he was enrolled in school, his mother died of tuberculosis, a disease that had also taken his father, at least one of his siblings, and which Mendeleev himself would battle as a young adult. A young professor In 1861, Mendeleev returned to Russia from research in Europe and later taught at the Technical Institute in St. Petersburg. He found that few of the new developments in the field

UNIT 3—STARS & ELEMENTS TEXT READER 10 of chemistry had made their way to his homeland — something he was determined to change, lecturing enthusiastically about the latest advances. Only 27 years old, he cultivated the persona of an eccentric, with a flowing beard and long, wild hair that he was known to trim only once a year. Still, he was a popular professor. Mendeleev recognized that there was no contemporary textbook on modern organic chemistry (concerned with carbon compounds, including living things), so he wrote one. His Organic Chemistry (1861) was considered his era’s most authoritative book on the subject. But the professor was painfully aware that many of his students “could not follow” him, as one student observed. Mendeleev knew that a critical reason for peoples’ difficulty in understanding chemistry was the lack of any clear system for classifying the known elements. Without one, he could only offer particulars about specific building blocks of matter, but no framework that would explain the relationships between different substances. As Mendeleev wrote: The edifice of science requires not only material, but also a plan, and necessitates the work of preparing the materials, putting them together, working out the plans and symmetrical proportions of the various parts. (Strathern, 2000) A missed train and a dream Next, Mendeleev began a text for inorganic chemistry (concerned with substances that are not organic, such as minerals), and the result, Principles of Chemistry (two volumes, 1868– 1870), would become the standard text for the field until early in the twentieth century. His research for this book would also lead him to his most renowned work. In 1867, when Mendeleev began writing Principles of Chemistry, he set out to organize and explain the elements. He began with what he called the “typical” elements: hydrogen, oxygen, nitrogen, and carbon. Those substances demonstrated a natural order for themselves. Next, he included the halogens, which had low atomic weights, reacted easily with other elements, and were readily available in nature. He had begun by using atomic weights as a principle of organization, but these alone did not present a clear system. At the time, elements were normally grouped in two ways: either by their atomic weight or by their common properties, such as whether they were metals or gases. Mendeleev’s breakthrough was to see that the two could be combined in a single framework. Mendeleev was said to have been inspired by the card game known as solitaire in North America, and “patience” elsewhere. In the game, cards are arranged both by suit, horizontally, and by number, vertically. To put some order into his study of chemical elements, Mendeleev made up a set of cards, one for each of the 63 elements known at the time. Mendeleev wrote the atomic weight and the properties of each element on a card. He took the cards everywhere he went. On February 17, 1869, right after breakfast, and with a train to catch later that morning, Mendeleev set to work organizing the elements with his

UNIT 3—STARS & ELEMENTS TEXT READER 11 cards. He carried on for three days and nights, forgetting the train and continually arranging and rearranging the cards in various sequences until he noticed some gaps in the order of atomic mass. As one story has it, Mendeleev, exhausted from his three-day effort, fell asleep. He later recalled, “I saw in a dream, a table, where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.” (Strathern, 2000) He named his discovery the “periodic table of the elements.” After his dream, Mendeleev drew the table he had envisioned. While arranging these cards of atomic data, Mendeleev discovered what is called the Periodic Law. When Mendeleev arranged the elements in order of increasing atomic mass, the properties where repeated. Because the properties repeated themselves regularly, or periodically, on his chart, the system became known as the periodic table. In devising his table, Mendeleev did not conform completely to the order of atomic mass. He swapped some elements around. We now know that the elements in the periodic table are not all in atomic mass order. Although he was unaware of it, Mendeleev had actually placed the elements in order of increasing “atomic number,” a number representing the amount of positively charged protons in the atom; also the number of negatively charged electrons that orbit the atom. Mendeleev went even further. He corrected the known atomic masses of some elements and he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered. He left blank spaces in his chart as placeholders to represent those unknown elements. When the gap was in the middle of a triad, or trio of elements bearing similar characteristics, he would guess at the hypothetical element’s atomic mass, atomic number, and other properties. Then he named these with the prefix eka, meaning “first” in Sanskrit. For instance, the predicted element designated as “eka-aluminum,” he located below the known element aluminum. It was later identified as gallium. Gallium, germanium, and scandium were all unknown in 1871, but Mendeleev left spaces for each and predicted their atomic masses and other chemical properties. Within 15 years, the “missing” elements were discovered, conforming to the basic characteristics Mendeleev had recorded. The accuracy of those predictions led to the periodic table’s acceptance. Building on others’ achievements Mendeleev did not develop the periodic table entirely on his own; he inherited and built on knowledge that was handed down from many chemists who spent their lives investigating matter. In the early 1800s, about 30 elements were known, and although chemists knew that some of these elements acted in similar ways or had similar characteristics, no one had found an overall, accepted pattern in their behaviors.

UNIT 3—STARS & ELEMENTS TEXT READER 12 In 1860, scientists met at one of the first international chemistry conferences. They decided that hydrogen, the lightest element, be given a weight of 1. All other elements’ weights would be compared to that of a hydrogen atom. That means that if an element is eight times heavier than hydrogen, its weight is 8. The concept of a systematic measure for atomic weights greatly contributed to the success of Mendeleev’s periodic table. In 1864, with about 50 elements known, the British chemist John Newlands noticed a pattern when he arranged the elements in order of atomic mass, or weight. He found that the properties of the elements seemed to repeat every eighth element. He called this the Law of Octaves, comparing it to musical scales. His ideas were rejected, and his peers joked that he may as well have arranged the elements in alphabetical order. After calcium (20 on today’s periodic table), Newlands’ order went amiss. He had grouped the very unreactive metal copper in the same group as the highly reactive elements lithium, sodium, and potassium. Far away in Russia, Mendeleev did not know about Newlands. As can happen in scientific developments, another researcher arrived at the same theory as Mendeleev’s at about the same time. In 1870, German chemist Julius Lothar Meyer published a paper describing the same organization of elements as Mendeleev’s. Both scientists had similar backgrounds: They had studied in Heidelberg, Germany, in the laboratory of the chemist Robert Bunsen. Both had attended, in September 1860, the first international chemistry congress in Karlsruhe, Germany. The congress had addressed the need to establish a common system to measure the weights of the different elements. And both chemists were teachers working on textbooks for their students. Was it fair that Mendeleev received all the credit for the periodic table while Meyer stayed unknown? It’s possible that this happened because Mendeleev, confident in his theory, published his findings first. Whatever the case, Mendeleev’s periodic table, with placeholders strategically saved for upcoming discoveries, provided invaluable scaffolding to classify the building blocks of matter. The spaces he reserved reflected a confidence, also, in the ongoing search for knowledge. Completing the puzzle The periodic table did not immediately affect the field of chemistry, though that changed with the discovery of the first missing element, gallium, in 1875. All of its qualities fit those Mendeleev had foreseen for the element he called eka-aluminum. As invaluable a reference tool as it was, the periodic table left plenty of room for discovery and enhancement. In the 1890s, an entirely new and unexpected group of elements was detected: the noble gases. They were added to the table as a separate column. Helium, the second-most abundant element in the Universe, wasn’t found on Earth until 1895. Another 60 or so elements have since been discovered and others may still be waiting to be found.

UNIT 3—STARS & ELEMENTS TEXT READER 13 Beneath the contiguous periodic table, you can see two rows known as the “lanthanides” (atomic numbers 57–71) and “actinides” (atomic numbers 89–103), named after the first, left- most members of their groups. As scientists found the heavier elements and began to create many more, the newer elements have been separated to keep the table’s cohesive shape. As of 2012, the periodic table has a total of 118 elements. Some elements have been named after scientists, such as atomic number 99, Einsteinium, for Albert Einstein. Rutherfordium, atomic number 104, is named in honor of physicist Ernest Rutherford, who developed the modern model of the atom. Atomic number 101, Mendelevium, is named after the periodic table’s architect. The matrix Mendeleev’s periodic table presented a new paradigm, with all of the elements positioned within a logical matrix. The elements are arranged in a series of rows called “periods,” so that those with similar properties appear in vertical columns. Each vertical column is called a “group,” or family, of elements. This instantly shows one set of relationships when read up and down, and another when read from side to side. Some groups have elements sharing very similar properties, such as their appearance and their behavior. For example, each element has its own melting and boiling point, the temperatures at which it changes from a solid to a liquid and from a liquid to a gas. Another characteristic is how “reactive” an element is, meaning how quick it is to join up with other elements. Scientists recognize how an element will react based on its location on the table. The elements are known by an atomic symbol of one or two letters. For example, the atomic symbol for gold is “Au,” the atom’s name is “gold,” and its atomic number is 79. The higher the atomic number, the “heavier” an element is said to be. Hydrogen is 1 on the periodic table, in the upper left corner. Its atomic number is 1; its nucleus contains one proton and one electron. About 98 percent of the Universe consists of the two lightest elements, hydrogen and helium. Continuing the mission Scientists continue to adjust the periodic table as new elements are found. Mendeleev’s mission, to clarify chemistry, lives on. He dedicated his textbook to his mother with what he claimed were her last words to him: Refrain from illusions; insist on work and not on words. Patiently seek divine and scientific truth. (Strathern, 2000)

UNIT 3—STARS & ELEMENTS TEXT READER 14 Dmitri Mendeleev: Building the Periodic Table of Elements (980L) By Michelle Feder, adapted by Newsela Russian chemist and teacher Dmitri Mendeleev created the periodic table, the system we use to classify the chemical elements. Organizing matter In the mid-1700s, chemists began identifying elements, which are substances made up of just one kind of atom. But a century later, they still used a variety of symbols and acronyms to represent the different materials. No common language existed to show how they related to each other. In 1869, the Russian chemist Dmitri Mendeleev changed all that. His diagram of elements, which make up all matter that exists, became known as the periodic table. Here’s what’s especially amazing: Mendeleev’s chart left spaces for elements that were yet to be discovered. For some of these missing pieces, he predicted what their atomic masses and other chemical properties would be. When scientists later discovered the elements Mendeleev had expected, the world saw the brilliance behind the periodic table. A difficult childhood Mendeleev was born in 1834 in the far west of Russia’s Siberia, the youngest of a dozen or more children. His family faced one crisis after another. When Dmitri was little, his father, a teacher, went blind, and his mother went to work. She became the manager of a glass factory. Tragedy struck again in 1848, when the factory burned down. The family faced poverty. Mendeleev’s mother was determined to get him an education, and traveled with him a great distance, to Moscow and then to St. Petersburg, to do so. Ten days after he was enrolled in school, his mother died of tuberculosis, a lung disease that had also taken his father, at least one of his siblings, and which Mendeleev himself would battle as a young adult. A young professor In 1861, Mendeleev returned to Russia from research in Europe. He found that few of the new developments in the field of chemistry had made their way to his homeland — something he was determined to change. He began lecturing enthusiastically about the latest advances. Only 27 years old, he had a quirky personality, with a flowing beard and long, wild hair that he was known to trim only once a year. Still, he became a popular professor. Mendeleev recognized that there was no modern textbook on modern organic chemistry (concerned with carbon compounds, including living things). So he wrote one. His Organic Chemistry (1861) was considered his era’s most authoritative book on the subject. But the professor was painfully aware that many of his students “could not follow” him, as one student observed. Mendeleev knew that a critical reason for peoples’ difficulty in

UNIT 3—STARS & ELEMENTS TEXT READER 15 understanding chemistry was the lack of any clear system for classifying the known elements. Without one, he could only offer particulars about specific building blocks of matter. A framework that would explain the relationships between different substances was still needed. A missed train and a dream Next, Mendeleev began a text for inorganic chemistry (concerned with substances that are not organic, such as minerals). Principles of Chemistry (written 1868–1870) would become the standard text for the field until early in the twentieth century. His research for this book would also lead him to his most famous work. In 1867, when Mendeleev began writing Principles of Chemistry, he set out to organize and explain the elements. He began with what he called the “typical” elements: hydrogen, oxygen, nitrogen, and carbon. Next he included the halogens. These had low atomic weights, reacted easily with other elements, and were readily available in nature. Chlorine — used to keep pools clean — is a halogen. Mendeleev begun using atomic weights as a principle of organization, but these alone did not present a clear system. At the time, elements were normally grouped in two ways: either by their atomic weight or by their common properties, such as whether they were metals or gases. Mendeleev’s breakthrough was to see that the two could be combined in a single framework. Mendeleev was said to have been inspired by the card game solitaire. In the game, cards are arranged both by suit, horizontally, and by number, vertically. To put some order into his study of chemical elements, Mendeleev made up a set of cards. Each represented one of the 63 elements known at the time. Mendeleev wrote the atomic weight and the properties of each element on a card. He took the cards everywhere he went. On February 17, 1869, with a train to catch that morning, Mendeleev set to work organizing the elements with his cards. He carried on for three days and nights, forgetting the train. He continually arranged and rearranged the cards in various orders until he noticed some gaps in the order of atomic mass. As one story has it, Mendeleev, exhausted from his three-day effort, fell asleep. He later recalled, “I saw in a dream, a table, where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.” He named his discovery the “periodic table of the elements.” While arranging these cards of atomic data, Mendeleev discovered what is called the Periodic Law. When Mendeleev arranged the elements in order of increasing atomic mass, the properties were repeated. Because the properties repeated themselves regularly, or periodically, on his chart, the system became known as the periodic table.

UNIT 3—STARS & ELEMENTS TEXT READER 16 In devising his table, Mendeleev did not completely follow the order of atomic mass. He swapped some elements around. We now know that the elements in the periodic table are not all in atomic mass order. Although he was unaware of it, Mendeleev had actually placed the elements in order of increasing “atomic number.” This number represents the amount of positively charged protons in the atom. It's also the number of negatively charged electrons that orbit the atom. Mendeleev went even further. He corrected the known atomic masses of some elements. And he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered. He left blank spaces in his chart as placeholders to represent those unknown elements. He would guess at hypothetical elements' atomic mass, atomic number, and other properties. Gallium, germanium, and scandium were all unknown in 1871, but Mendeleev left spaces for each and predicted their atomic masses and other chemical properties. Within 15 years, the “missing” elements were discovered. Amazingly, they conformed to the basic characteristics Mendeleev had recorded. The accuracy of those predictions led to the periodic table’s acceptance. Building on others’ achievements Mendeleev did not develop the periodic table entirely on his own; he inherited and built on knowledge that was handed down from many chemists who spent their lives investigating matter. In the early 1800s, about 30 elements were known. By then chemists knew that some of these elements acted in similar ways or had similar characteristics. However, no one had found an overall, accepted pattern in their behaviors. In 1860, scientists met at one of the first international chemistry conferences. They decided that hydrogen, the lightest element, be given a weight of 1. All other elements’ weights would be compared to that of a hydrogen atom. That means that if an element is eight times heavier than hydrogen, its weight is 8. The concept of a systematic measure for atomic weights greatly contributed to the success of Mendeleev’s periodic table. As can happen in scientific developments, other researchers arrived at the same theory as Mendeleev’s at about the same time. In 1870, German chemist Julius Lothar Meyer published a paper describing the same organization of elements as Mendeleev’s. Was it fair that Mendeleev received all the credit for the periodic table while Meyer stayed unknown? It’s possible that this happened because Mendeleev, confident in his theory, published his findings first. Whatever the case, Mendeleev’s periodic table provided invaluable at classifying the building blocks of matter. The spaces he reserved for upcoming discoveries reflected a confidence, also, in the continuing search for knowledge.

UNIT 3—STARS & ELEMENTS TEXT READER 17 Completing the puzzle As invaluable a reference tool as it was, the periodic table left plenty of room for discovery and enhancement. In the 1890s, an entirely new and unexpected group of elements was detected: the noble gases. They were added to the table as a separate column. Helium, the second-most abundant element in the Universe, wasn’t found on Earth until 1895. Another 60 or so elements have since been discovered and others may still be waiting to be found. Beneath the main periodic table, you can see two rows. They're known as the “lanthanides” (atomic numbers 57–71) and “actinides” (atomic numbers 89–103). As scientists found the heavier elements and began to create many more, the newer elements have been separated to keep the table’s shape intact. As of 2012, the periodic table has a total of 118 elements. Some elements have been named after scientists, such as atomic number 99, Einsteinium, for Albert Einstein. Rutherfordium, atomic number 104, is named in honor of physicist Ernest Rutherford, who developed the modern model of the atom. Atomic number 101, Mendelevium, is named after the periodic table’s architect. The matrix Mendeleev’s periodic table presented a new paradigm, with all of the elements positioned within a logical matrix. The elements are arranged in a series of rows called “periods,” so that those with similar properties appear in vertical columns. Each vertical column is called a “group,” or family, of elements. This instantly shows one set of relationships when read up and down, and another when read from side to side. Some groups have elements sharing very similar properties, such as their appearance and their behavior. For example, each element has its own melting and boiling point, the temperatures at which it changes from a solid to a liquid and from a liquid to a gas. Another characteristic is how “reactive” an element is, meaning how quick it is to join up with other elements. Scientists recognize how an element will react based on its location on the table. The elements are known by an atomic symbol of one or two letters. For example, the atomic symbol for gold is “Au,” the atom’s name is “gold,” and its atomic number is 79. The higher the atomic number, the “heavier” an element is said to be. Hydrogen is 1 on the periodic table, in the upper left corner. Its atomic number is 1; its nucleus contains one proton and one electron. About 98 percent of the Universe consists of the two lightest elements, hydrogen and helium. Continuing the mission Scientists continue to adjust the periodic table as new elements are found. Mendeleev’s mission, to clarify chemistry, lives on. He dedicated his textbook to his mother with what he claimed were her last words to him:

UNIT 3—STARS & ELEMENTS TEXT READER 18 Refrain from illusions; insist on work and not on words. Patiently seek divine and scientific truth.

Dmitri Mendeleev: Building the Periodic Table of Elements (890 L) By Michelle Feder, adapted by Newsela Russian chemist and teacher Dmitri Mendeleev created the system we use to classify the chemical elements, called the periodic table. Organizing matter In the mid-1700s, chemists began to identify elements, the building blocks of matter. Elements are pure substances made up of just one kind of atom, like gold and silver. Unlike compounds, elements can't be broken down any more. At the time, scientists used a variety symbols for elements. No common language existed to explain how elements related to each other. In 1869, the Russian chemist Dmitri Mendeleev came up with one. His diagram of elements made him famous and became known as the periodic table. It contains the building blocks of all matter that exists in the world. Here’s what’s especially amazing: Mendeleev’s chart left spaces for elements that were yet to be discovered. For some of these missing pieces, he predicted what their atomic masses and other chemical properties would be. Later on, scientists discovered the elements Mendeleev expected. It proved the brilliance behind the periodic table. A difficult childhood Mendeleev was born in 1834 in the far west of Russia’s Siberia. He was the youngest of a dozen or more children. His family faced one crisis after another. When Dmitri was little, his father went blind, and his mother went to work. She became the manager of a glass factory. Tragedy struck again in 1848 when the factory burned down. The family faced poverty. Yet, Mendeleev’s mother was determined to get him an education. She traveled with him a great distance to St. Petersburg to do so. Ten days after he was enrolled in school, his mother died of tuberculosis. The lung disease had also taken his father, and at least one of his siblings. Mendeleev himself would battle it as a young adult. A young professor The young Mendeleev went to Europe to study the latest advances in science. Upon his return to Russia in 1861, he found that few of the new developments in the field of chemistry had made their way to his homeland. He was determined to change that. So he lectured enthusiastically about the latest advances. Only 27 years old, he developed an eccentric personality with a flowing beard and long, wild hair that he was known to trim only once a year. Still, he became a popular professor.

UNIT 3—STARS & ELEMENTS TEXT READER 19 Mendeleev saw that there was no modern textbook on organic chemistry. Organic chemists study compounds containing the element carbon, which all life depends on. So, Mendeleev wrote a textbook on organic chemistry. But Mendeleev was painfully aware that many of his students “could not follow” him, as one student observed. He knew that a critical reason for peoples’ difficulty in understanding chemistry was the lack of any clear system for classifying elements. Without one, he couldn't explain the relationships between different substances. A missed train and a dream Next, Mendeleev began a textbook for inorganic chemistry. Unlike organic chemistry, it is concerned with nonliving, inorganic substances, such as minerals. In 1867, when Mendeleev began writing his book, he set out to organize and explain the elements. He began with what he called the “typical” elements: hydrogen, oxygen, nitrogen, and carbon. Those substances demonstrated a natural order for themselves. Next he included the halogens. These had low atomic weights, reacted easily with other elements, and were readily available in nature. At the time, elements were normally grouped in two ways: either by their atomic weight or by their common properties, such as whether they were metals or gases. Mendeleev had a breakthrough. The two ways of grouping elements could be combined. Mendeleev was said to have been inspired by the card game known as solitaire. In the game, cards are arranged both by suit, horizontally, and by number, vertically. To put some order into his study of chemical elements, Mendeleev made up a set of cards. Each represented one of the 63 elements known at the time. Mendeleev wrote the atomic weight and the properties of each element on a card. He took the cards everywhere he went. On February 17, 1869, with a train to catch that morning, Mendeleev set to work organizing the elements with his cards. He carried on for three days and nights, forgetting the train. He arranged and rearranged the cards in various orders constantly. Finally, he noticed some gaps in the order of atomic mass. As one story has it, Mendeleev, exhausted from his three-day effort, fell asleep. He later recalled, “I saw in a dream, a table, where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.” He named his discovery the “periodic table of the elements.” While arranging these cards of atomic data, Mendeleev discovered what is called the Periodic Law. Mendeleev arranged the elements in order of increasing atomic mass. He noticed that the properties were repeated. Because the properties on his chart repeated themselves regularly, or periodically, the system became known as the periodic table. In devising his table, Mendeleev did not completely follow the order of atomic mass. He swapped some elements around. We now know that the elements in the periodic table are not

UNIT 3—STARS & ELEMENTS TEXT READER 20 all in atomic mass order. Although he was unaware of it, Mendeleev had actually placed the elements in order of increasing “atomic number.” This number represents the amount of positively charged protons in the atom. It's also the number of negatively charged electrons that orbit the atom. Mendeleev went even further. He corrected the known atomic masses of some elements. And he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered. He left blank spaces in his chart as placeholders to represent those unknown elements. He would guess at atomic mass, atomic number, and other properties of hypothetical elements. Gallium, germanium, and scandium were all unknown in 1871. However, Mendeleev left spaces for each and predicted their atomic masses. Within 15 years, the “missing” elements were discovered. Amazingly, they conformed to the basic characteristics Mendeleev had recorded. The accuracy of those predictions led to the periodic table’s acceptance. Building on others’ achievements Mendeleev did not develop the periodic table entirely on his own; he built on knowledge handed down from chemists who came before him. In the early 1800s, about 30 elements were known. By then chemists knew that some of these elements acted in similar ways or had similar characteristics. However, no one had found an overall pattern in their behaviors. In 1860, scientists met at one of the first international chemistry conferences. They decided that hydrogen, the lightest element, be given a weight of 1. All other elements’ weights would be compared to that of a hydrogen atom. That means that if an element is eight times heavier than hydrogen, its weight is 8. As can happen in science, another researcher arrived at the same theory as Mendeleev’s at about the same time. In 1870, German chemist Julius Lothar Meyer published a paper describing the same organization of elements as Mendeleev’s. Was it fair that Mendeleev received all the credit for the periodic table while Meyer stayed unknown? It’s possible that this happened because Mendeleev published his findings first. Whatever the case, Mendeleev’s periodic table provided invaluable at classifying the building blocks of matter. Completing the puzzle As invaluable as the periodic table was, it left plenty of room for discovery and improvement. In the 1890s, an entirely new and unexpected group of elements was detected: the noble gases. They were added to the table as a separate column. Helium, the second-most abundant element in the Universe, wasn’t found on Earth until 1895. Another 60 or so elements have since been discovered. Others may still be waiting to be found.

UNIT 3—STARS & ELEMENTS TEXT READER 21 Beneath the main periodic table, you can see two rows. They're known as the “lanthanides” (atomic numbers 57–71) and “actinides” (atomic numbers 89–103). As scientists found the heavier elements and began to create many more, the newer elements have been separated to keep the table’s shape intact. As of 2012, the periodic table has a total of 118 elements. Some elements have been named after scientists. Atomic number 99 is called Einsteinium, for Albert Einstein. Rutherfordium, atomic number 104, is named in honor of physicist Ernest Rutherford, who developed the modern model of the atom. Atomic number 101, Mendelevium, is named after the periodic table’s inventor. The matrix Mendeleev’s periodic table presented a new standard. Now all of the elements were positioned in a logical order. The elements are arranged in a series of rows called “periods,” so that those with similar properties appear in vertical columns. Each vertical column is called a “group,” or family, of elements. This instantly shows one set of relationships when read up and down, and another when read from side to side. Some groups have elements sharing very similar properties, such as their appearance and their behavior. For example, each element has its own melting and boiling point, the temperatures at which it changes from a solid to a liquid and from a liquid to a gas. Another characteristic is how “reactive” an element is, meaning how quick it is to join up with other elements. Scientists recognize how an element will react based on its location on the table. The elements are known by an atomic symbol of one or two letters. For example, the atomic symbol for gold is “Au,” the atom’s name is “gold,” and its atomic number is 79. The higher the atomic number, the “heavier” an element is said to be. Hydrogen is 1 on the periodic table, in the upper left corner. Its atomic number is 1; its nucleus contains one proton and one electron. About 98 percent of the Universe consists of the two lightest elements, hydrogen and helium. Continuing the mission Scientists continue to adjust the periodic table as new elements are found. Mendeleev’s mission to clarify chemistry lives on. He dedicated his textbook to his mother with what were her last words to him: Refrain from illusions; insist on work and not on words. Patiently seek divine and scientific truth.

Dmitri Mendeleev: Building the Periodic Table of Elements (780 L) By Michelle Feder, adapted by Newsela

UNIT 3—STARS & ELEMENTS TEXT READER 22 Russian chemist Dmitri Mendeleev created the system we use to organize the chemical elements: the periodic table. Organizing matter In the mid-1700s, chemists began to identify the building blocks of matter, called elements. Elements, such as gold and silver, are made up of just one kind of atom. Unlike compounds, they can't be broken down further. At the time, scientists used a variety symbols for elements. No common language existed to explain how elements related to each other. In 1869, the Russian chemist Dmitri Mendeleev changed that. He diagrammed the elements. His list of the basic ingredients of all life became known as the periodic table. It contains the building blocks of all matter that exists. Here’s what’s especially amazing: Mendeleev’s chart left spaces for elements that hadn't yet been discovered. For some of these missing pieces, he predicted what their atomic masses would be. Later on, scientists discovered the elements Mendeleev predicted. It proved the brilliance behind his periodic table. A difficult childhood Mendeleev was born in 1834 in Siberia, Russia. He was the youngest of a dozen or more children. His family faced one crisis after another. When Dmitri was little, his father went blind, and his mother went to work. She became the manager of a glass factory. Tragedy struck again in 1848 when the factory burned down. The family faced poverty. But, Mendeleev’s mother was determined to get him an education. She traveled with him a great distance to St. Petersburg to do so. Ten days after he was enrolled in school, his mother died of tuberculosis. The lung disease had also taken his father and at least one of his siblings. Mendeleev himself would battle it as a young adult. A young professor The young Mendeleev went to Europe to study the latest advances in science. He returned home to Russia in 1861. Upon arriving, he found that the newest developments in chemistry hadn't made their way to his homeland. He was determined to change that. So he lectured enthusiastically about the latest advances. Only 27 years old, he had a quirky personality. He grew a flowing beard and long, wild hair that he was known to trim only once a year. Still, he became a popular professor. Mendeleev saw that there was no modern textbook on organic chemistry. Organic chemists study compounds containing the element carbon, which all life depends on. So, Mendeleev wrote a textbook on organic chemistry. But the professor realized that many of his students could not follow along. Mendeleev knew that chemistry was difficult to understand. At the time, no real system existed for classifying elements. Without one, he couldn't explain the relationships between different substances.

UNIT 3—STARS & ELEMENTS TEXT READER 23 A missed train and a dream Next, Mendeleev began a textbook for inorganic chemistry. Unlike organic chemistry, it is concerned with nonliving, inorganic substances, such as minerals. In 1867, when Mendeleev began writing his book on inorganic chemistry, he set out to organize and explain the elements. He began with what he called the “typical” elements: hydrogen, oxygen, nitrogen, and carbon. Next he included the halogens. They had low atomic weights, reacted easily with other elements, and were readily available in nature. Chlorine, which keeps swimming pools clean, is a halogen. At the time, elements were normally grouped in two ways: either by their atomic weight or by their common properties, such as whether they were metals or gases. Mendeleev had a breakthrough. The two ways of grouping elements could be combined. Mendeleev was inspired by the card game solitaire. In the game, cards are arranged both by suit, horizontally, and by number, vertically. Mendeleev made up his own set of cards. Each represented one of the 63 elements known at the time. Mendeleev wrote the atomic weight and the properties of each element on a card. He took the cards everywhere he went. On February 17, 1869, with a train to catch later that morning, Mendeleev set to work organizing the elements with his cards. He carried on for three days and nights, forgetting the train. He arranged and rearranged the cards in various orders. Finally, he noticed some gaps in the order of atomic mass. As one story has it, Mendeleev, exhausted from his three-day effort, fell asleep. He later recalled, “I saw in a dream, a table, where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper.” He named his discovery the “periodic table of the elements.” While arranging these cards of atomic data, Mendeleev discovered what is called the Periodic Law. Mendeleev arranged the elements in order of increasing atomic mass. He noticed that the properties were repeated. Because the properties on his chart repeated themselves regularly, or periodically, the system became known as the periodic table. In coming up with his table, Mendeleev did not completely follow the order of atomic mass. He swapped some elements around. Although he was unaware of it, Mendeleev had actually placed the elements in order of increasing “atomic number.” This number represents the amount of positively charged protons in the atom. It's also the number of negatively charged electrons that orbit the atom. Mendeleev went even further. He used the patterns in his table to predict the atomic mass and atomic number of the elements he thought must exist. He left blank spaces in his chart for them. Gallium, germanium, and scandium were all unknown in 1871. However, Mendeleev left placeholders for each and predicted their atomic masses. Within 15 years, the “missing”

UNIT 3—STARS & ELEMENTS TEXT READER 24 elements were discovered. Amazingly, they fit the basic characteristics Mendeleev had recorded. The accuracy of those predictions led people to accept the periodic table. Building on others’ achievements Mendeleev did not develop the periodic table entirely on his own. His work was built upon knowledge handed down by chemists before him. In the early 1800s, about 30 elements were known. By then chemists knew that some of these elements acted in similar ways. However, no one had found an overall pattern in their behaviors. In 1860, scientists met at one of the first international chemistry conferences. Hydrogen is the lightest element. So, they decided to give it a weight of 1. All other elements’ weights would be compared to an atom of hydrogen. That means that if an element is eight times heavier than hydrogen, its weight is 8. Completing the puzzle As impressive as the periodic table was, it left plenty of room for discovery and improvement. In the 1890s, an entirely new and unexpected group of elements was detected: the noble gases. They were added to the table as a separate column. Helium, the second-most common element in the Universe, wasn’t found on Earth until 1895. Another 60 or so elements have since been discovered. Others have been invented by humans. Some may still be found. Beneath the main periodic table, you can see two rows. They're known as the “lanthanides” (atomic numbers 57–71) and “actinides” (atomic numbers 89–103). Since Mendeleev's time, scientists have found heavier elements. Scientists also began to create their own elements artificially. To keep the table’s shape unbroken, the newer elements have been separated. As of 2012, the periodic table has a total of 118 elements. Some elements have been named after scientists. Atomic number 99 is called Einsteinium, for Albert Einstein. Rutherfordium, atomic number 104, is named in honor of physicist Ernest Rutherford. He developed the modern model of the atom. Atomic number 101, Mendelevium, is named after the periodic table’s inventor. The matrix Mendeleev’s periodic table created a new standard. Now all of the elements were in a logical order. The elements are arranged in a series of rows called “periods.” Those with similar properties appear in vertical columns. Each vertical column is called a “group,” or family, of elements. This instantly shows one set of relationships when read up and down. You see another when reading from side to side. Some groups have elements sharing very similar properties, such as their appearance and their behavior. For example, each element has its own melting point, the temperature at which it changes from a solid to a liquid. Each has a boiling point where it goes from a liquid

UNIT 3—STARS & ELEMENTS TEXT READER 25 to a gas. Another characteristic is how “reactive” an element is, meaning how quick it is to join up with other elements. Scientists can guess how an element will react based on its location on the table. The elements are known by an atomic symbol of one or two letters. For example, the atomic symbol for gold is “Au,” and the atom’s name is “gold.” Its atomic number is 79. The higher the atomic number, the “heavier” an element is said to be. Hydrogen is 1 on the periodic table, in the upper left corner. Its atomic number is 1. Hydrogen's nucleus contains one proton and one electron. About 98 percent of the Universe consists of the two lightest elements, hydrogen and helium. Continuing the mission Scientists continue to adjust the periodic table as new elements are found. Mendeleev’s mission to make chemistry clear lives on. He dedicated his textbook to his mother with what were her last words to him: Refrain from illusions; insist on work and not on words. Patiently seek divine and scientific truth.

UNIT 3—STARS & ELEMENTS TEXT READER 26 Marie Curie: Chemistry, Physics, and Radioactivity

Using a makeshift work space, Curie began, in 1897, experiments that would pioneer the science of radioactivity, change medicine, and increase our understanding of the structure of atoms.

Marie Curie: Chemistry, Physics, and Radioactivity (1060 L) By Michelle Feder Using a makeshift workspace, Marie Curie began, in 1897, a series of experiments that would pioneer the science of radioactivity, change the world of medicine, and increase our understanding of the structure of the atom. Early life and overcoming obstacles Marie Curie became famous for the work she did in Paris. But she was born in Warsaw, Poland, in 1867, as Maria Sklodowska. She was the youngest of five children, and both of her parents were educators: Her father taught math and physics, and her mother was headmistress of a private school for girls. Circumstances changed for Maria’s family the year she turned 10. Her mother died, and her father lost his job. Her father rented bedrooms to boarders, and Maria had to sleep on the floor. Even as a young girl, Maria was interested in science. Her father kept scientific instruments at home in a glass cabinet, and she was fascinated by them. Maria proved herself early as an exceptional student. At that time, Russia ruled Poland, and children had to speak Russian at school; indeed, it was against the law to teach Polish history or the Polish language. Nevertheless, Maria graduated from high school when she was 15 with top grades. She wanted to continue her education in physics and math, but it would be decades before the University of Warsaw admitted women. Maria knew she would have to leave Poland to further her studies, and she would have to earn money to make the move. Maria’s sister Bronya, meanwhile, wanted to study medicine. Together, they made a deal: Maria would work to help pay for Bronya’s medical studies. Then, when Bronya was a doctor, she would help pay for Maria’s education. When Maria’s turn came, she did not want to leave her family or country, but knew it was necessary. She chose Paris because she wanted to attend the great university there: the University of Paris — the Sorbonne — where she would have the chance to learn from many of the era’s leading thinkers.

UNIT 3—STARS & ELEMENTS TEXT READER 27 In Paris When Maria registered at the Sorbonne, she signed her name as “Marie,” and worked hard to learn French. Of 1,800 students there, only 23 were women. Many people still believed that women should not be studying science, but Marie was a dedicated student. She rented a small space in an attic and often studied late into the night. In 1893, Marie took an exam to get her degree in physics, a branch of science that studies natural laws, and passed, with the highest marks in her class. She was the first woman to earn a degree in physics from the Sorbonne. Marie thought seriously about returning to Poland and getting a job as a teacher there. But she met a French scientist named Pierre Curie, and on July 26, 1895, they were married. They rented a small apartment in Paris, where Pierre earned a modest living as a college professor, and Marie continued her studies at the Sorbonne. In September 1897, Marie gave birth to a daughter, Irène. Meanwhile, scientists all over the world were making dramatic discoveries. The year the Curies were married, a German scientist named Wilhelm Roentgen discovered what he called “X-radiation” (X-rays), the electromagnetic radiation released from some chemical materials under certain conditions. This breakthrough served as a catalyst for Marie’s own work. Other scientists began experimenting with X-rays, which could pass through solid materials. While researching the source of X-rays, French physicist Antoine Henri Becquerel found that uranium gave off an entirely new form of invisible ray, a narrow beam of energy. Marie Curie wanted to know why. One of her greatest achievements was solving this mystery. Radiant discoveries Marie Curie, and other scientists of her time, knew that everything in nature is made up of elements. Elements are materials that can’t be broken down into other substances, such as gold, uranium, and oxygen. When Marie was born, there were only 63 known elements. (Today 118 elements have been identified.) At the time she began her work, scientists thought they had found all the elements that existed. But they were wrong. Marie began testing various kinds of natural materials. One substance was a mineral called “pitchblende.” Scientists believed it was made up mainly of oxygen and uranium. But Marie’s tests showed that pitchblende produced much stronger X-rays than those two elements did alone. She began to think there must be an undiscovered element in pitchblende that made it so powerful. To prove it, she needed loads of pitchblende to run tests on the material and a lab to test it in. Pierre helped her find an unused shed behind the Sorbonne’s School of Physics and Chemistry. There, Marie put the pitchblende in huge pots, stirred and cooked it, and ground it into powder. She added chemicals to the substance and tried to isolate all the elements in it. Every day she mixed a boiling mass with a heavy iron rod nearly as large as herself.

UNIT 3—STARS & ELEMENTS TEXT READER 28 After months of this tiring work, Marie and Pierre found what they were looking for. In 1898, Marie discovered a new element that was 400 times more radioactive than any other. They named it “polonium,” after her native country. Later that year, the Curies announced the existence of another element they called “radium,” from the Latin word for “ray.” It gave off 900 times more radiation than polonium. Marie also came up with a new term to define this property of matter: “radioactive.” It took the Curies four laborious years to separate a small amount of radium from the pitchblende. In 1902, the Curies finally could see what they had discovered. Inside the dusty shed, the Curies watched its silvery-blue-green glow. Marie later remembered this vividly: “One of our pleasures was to enter our workshop at night. Then, all around us, we would see the luminous silhouettes of the beakers and capsules that contained our products.” (Santella, 2001) Marie presented her findings to her professors. She suggested that the powerful rays, or energy, the polonium and radium gave off were actually particles from tiny atoms that were disintegrating inside the elements. Marie’s findings contradicted the widely held belief that atoms were solid and unchanging. Originally, scientists thought the most significant learning about radioactivity was in detecting new types of atoms. But the Curies’ research showed that the rays weren’t just energy released from a material’s surface, but from deep within the atoms. This discovery was an important step along the path to understanding the structure of the atom. A woman of distinction In 1903, Marie received her doctorate degree in physics, which was the first PhD awarded to a woman in France. In November of the same year, Pierre was nominated for the Nobel Prize, but without Marie. He sent a letter to the nominating committee expressing a wish to be considered together with her. For their discovery of radioactivity, the couple, along with Henri Becquerel, shared the Nobel Prize in physics. Marie Curie was the first woman to receive a Nobel Prize. After many years of hard work and struggle, the Curies had achieved great renown. But there was one serious problem. The Curies were unable to travel to Sweden to accept the Nobel Prize because they were sick. Both of them suffered from what later was recognized as radiation sickness. Marie coughed and lost weight; they both had severe burns on their hands and tired very quickly. All of this came from handling radioactive material. At the time, scientists didn’t know the dangers of radioactivity. The Nobel (accepted on the Curies’ behalf by a French official in Stockholm) contributed to a better life for the couple: Pierre became a professor at the Sorbonne, and Marie became a teacher at a women’s college. The Sorbonne still did not allow women professors. The prize itself included a sum of money, some of which Marie used to help support poor students from Poland.

UNIT 3—STARS & ELEMENTS TEXT READER 29 In 1904, Marie gave birth to Eve, the couple’s second daughter. Around that time, the Sorbonne gave the Curies a new laboratory to work in. But on April 19, 1906, this period came to a tragic end. On a busy street, Pierre Curie was hit by a horse-drawn carriage. He died instantly. Only 39 years old when she was widowed, Marie lost her partner in work and life. Marie struggled to recover from the death of her husband, and to continue his laboratory work and teaching. Though the university did not offer her his teaching job immediately, it soon realized she was the only one who could take her husband’s place. On November 5, 1906, as the first female professor in the Sorbonne’s history, Marie Curie stepped up to the podium and picked up where Pierre had left off. Around her, a new age of science had emerged. A chemistry of the invisible An atom is the smallest particle of an element that still has all the properties of the element. Periodic table creator Dmitri Mendeleev and other scientists had insisted that the atom was the smallest unit in matter, but the English physicist J. J. Thompson, responding to X-ray research, concluded that certain rays were made up of particles even smaller than atoms. The work of Thompson and Curie contributed to the work of New Zealand–born British scientist Ernest Rutherford, a Thompson protégé who, in 1899, distinguished two different kinds of particles emanating from radioactive substances: “beta” rays, which traveled nearly at the speed of light and could penetrate thick barriers, and the slower, heavier “alpha” rays. Marie considered radioactivity an atomic property, linked to something happening inside the atom itself. Rutherford, working with radioactive materials generously supplied by Marie, researched his “transformation” theory, which claimed that radioactive elements break down and actually decay into other elements, sending off alpha and beta rays. The Curies had resisted the decay theory at first but eventually came around to Rutherford’s perspective. It confirmed Marie’s theory that radioactivity was a subatomic property. In 1904, Rutherford came up with the term “half-life,” which refers to the amount of time it takes one-half of an unstable element to change into another element or a different form of itself. This would later prove an important discovery for radiometric dating when scientists realized they could use “half-lives” of certain elements to measure the age of certain materials. In 1905, an amateur Swiss physicist, Albert Einstein, was also studying unstable elements. According to his calculation, very small amounts of matter were capable of turning into huge amounts of energy, a premise that would lead to his General Theory of Relativity a decade later. In 1906, Marie voiced her acceptance of Rutherford’s decay theory. By then, Thompson was calling the particles smaller than atoms “electrons,” the first subatomic particles to be identified. Thompson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases. In

UNIT 3—STARS & ELEMENTS TEXT READER 30 1911, Rutherford made another breakthrough, building upon Thompson’s earlier theory about the structure of the atom. He outlined a new model for the atom: mostly empty space, with a dense “nucleus” in the center containing “protons.” Marie’s isolation of radium had provided the key that opened the door to this area of knowledge. She had created what she called “a chemistry of the invisible.” The age of nuclear physics had begun. A second Nobel Prize In the years after Pierre’s death, Marie juggled her responsibilities and roles as a single mother, professor, and esteemed researcher. She wanted to learn more about the elements she discovered and figure out where they fit into Mendeleev’s table of the elements, now referred to as the “periodic table.” Elements on the table are arranged by weight. To determine the locations for polonium and radium, she needed to figure out their molecular weight. Her research showed that polonium should be number 84 and radium should be 88. In 1911, Marie was awarded the Nobel Prize for Chemistry, becoming the first person to win two Nobel Prizes. This time, she traveled to accept the award in Sweden, along with her daughters. Marie was recognized for her work isolating pure radium, which she had done through chemical processes. A year later, Marie was visited by Einstein and his family. The two scientists had much to discuss: What was the source of this immense energy that came from radioactive elements? To promote continued research on radioactivity, Marie established the Radium Institute, a leading research center in Paris and later in Warsaw, with Marie serving as director from 1914 until her death in 1934. Marie Curie’s radioactivity research indelibly influenced the field of medicine. In 1904, the first textbook that described radium treatments for cancer patients was published. During World War I, she designed radiology cars bringing X-ray machines to hospitals for soldiers wounded in battle. She also equipped and staffed 200 permanent radiology posts in hospitals. Marie trained women as well as men to be radiologists. In the last two years of the war, more than a million soldiers were X-rayed and many were saved. Her research laid the foundation for the field of radiotherapy (not to be confused with chemotherapy), which uses ionizing radiation to destroy cancerous tumors in the body. Marie Curie died of a type of leukemia, and we now know that radioactivity caused many of her health problems. In the 1920s scientists became aware of the dangers of radiation exposure: The energy of the rays speeds through the skin, slams into the molecules of cells, and can harm or even destroy them.

UNIT 3—STARS & ELEMENTS TEXT READER 31 A place in the periodic table In 1944, scientists at the University of California–Berkeley discovered a new element, 96, and named it “curium,” in honor of Marie and Pierre. Today we recognize 118 elements, 92 formed in nature and the others created artificially in labs. Marie Curie’s legacy cannot be overstated. Poverty didn’t stop her from pursuing an advanced education. Marriage enhanced her life and career, and motherhood didn’t limit her life’s work. At a time when men dominated science and women didn’t have the right to vote, Marie Curie proved herself a pioneering scientist in chemistry and physics.

Marie Curie: Chemistry, Physics, and Radioactivity (920 L) By Michelle Feder, adapted by Newsela In a humble workspace in 1897, Marie Curie began a series of experiments in the science of radioactivity that would change the world of medicine, and increase our understanding of the structure of the atom. Early life and overcoming obstacles Marie Curie became famous for the work she did in France. But she was born in Warsaw, Poland, in 1867, as Maria Sklodowska. She was the youngest of five children, and both of her parents were educators: Her father taught math and physics, and her mother was headmistress of a private school for girls. But things took a turn for the worse the year she turned 10. Her mother died, and her father lost his job. Her father rented bedrooms to boarders, and Maria had to sleep on the floor. Even as a young girl, Maria was interested in science. Her father kept scientific instruments at home in a glass cabinet, and she was fascinated by them. Maria proved herself early as an exceptional student. She wanted to continue her education in physics and math, but the University of Warsaw didn't admit women. Maria knew she would have to leave Poland to further her studies. Maria did not want to leave her family or country, but knew it was necessary. She chose Paris because she wanted to attend the great university there: the University of Paris — the Sorbonne. There she would have the chance to learn from many of the era’s most brilliant thinkers. In Paris When Maria registered at the Sorbonne, she signed her name as “Marie,” and worked hard to learn French. Of 1,800 students there, only 23 were women. She became the first woman to earn a degree in physics from the Sorbonne.

UNIT 3—STARS & ELEMENTS TEXT READER 32 In France, she met a scientist named Pierre Curie, and on July 26, 1895, they were married. They rented a small apartment in Paris, where Pierre earned a modest living as a college professor. Marie continued her studies at the Sorbonne. In September 1897, Marie gave birth to a daughter, Irène. Meanwhile, scientists all over the world were making dramatic discoveries. The year the Curies were married, a German scientist named Wilhelm Roentgen discovered what he called “X-radiation” (X-rays). These rays are electromagnetic radiation and can glow like visible light. They're released from some chemical materials under certain conditions. Roentgen accidentally discovered X-rays in his lab. One day, he saw X-rays glowing through black cardboard he'd placed around a tube filled with gas. Roentgen's breakthrough pushed Marie’s own work forward. Other scientists began experimenting with X-rays. Their ability to pass through solid materials led to the X-ray machine which can see inside the human body. While studying X- rays, French physicist Antoine Henri Becquerel found that uranium gave off an entirely new form of invisible ray, a narrow beam of energy. Marie Curie wanted to know why. One of her greatest achievements was solving this mystery. Radiant discoveries Marie Curie, and other scientists of her time, knew that everything in nature is made up of elements. Elements are materials, such as gold, uranium, and oxygen, that can’t be broken down into other substances. When Marie was born, there were only 63 known elements. Today 118 elements have been identified. At the time she began her work, scientists thought they had found all the elements that existed. But they were wrong. Marie began testing various kinds of natural materials. One substance was a mineral called “pitchblende.” Scientists believed it was made up mainly of oxygen and uranium. But Marie’s tests showed that pitchblende produced much stronger X-rays than those two elements did alone. She began to think there must be one or more undiscovered elements in pitchblende that made it so powerful. To prove it, she needed loads of pitchblende to run tests on the material and a lab to test it in. Pierre helped her find an unused shed at the Sorbonne. There, Marie put the pitchblende in huge pots, stirred and cooked it, and ground it into powder. She added chemicals to the substance and tried to separate the elements in it. Every day she mixed a boiling mass with a heavy iron rod nearly as large as herself. After months of this tiring work, Marie and Pierre found what they were looking for. In 1898, Marie discovered a new element that was 400 times more radioactive than any other. They named it “polonium,” after her native country. Later that year, the Curies announced the existence of another element they called “radium,” from the Latin word for “ray.” It gave off 900 times more radiation than polonium. Marie also came up with a new term for this property of matter: “radioactive.”

UNIT 3—STARS & ELEMENTS TEXT READER 33 It took the Curies four hard years to separate a small amount of radium from the pitchblende. In 1902, the Curies finally could see what they had discovered. Inside the dusty shed, the Curies watched its silvery-blue-green glow. Marie later remembered this vividly: “One of our pleasures was to enter our workshop at night. Then, all around us, we would see the luminous silhouettes of the beakers and capsules that contained our products.” Marie presented her findings to her professors. She suggested that the powerful rays, or energy the polonium and radium gave off, were actually particles from tiny atoms. The atoms were disintegrating inside the elements and giving off energy. Marie’s findings contradicted the widely held belief that atoms were solid and unchanging. The Curies’ research showed that the rays weren’t just energy released from a material’s surface, but from deep within the atoms. This discovery was an important step to understanding the structure of the atom. A woman of distinction In 1903, Marie received her doctorate degree in physics, which was the first PhD awarded to a woman in France. For their discovery of radioactivity, the couple won the Nobel Prize in physics. Marie Curie was the first woman to receive a Nobel Prize. After many years of hard work and struggle, the Curies had achieved great fame. But there was one serious problem. Both of them suffered from what later was recognized as radiation sickness. Marie coughed and lost weight; they both had severe burns on their hands and tired very quickly. All of this came from handling radioactive material. At the time, scientists didn’t know the dangers of radioactivity. The Nobel contributed to a better life for the couple: Pierre became a professor at the Sorbonne, and Marie became a teacher at a women’s college. The Sorbonne still did not allow women professors. The Nobel prize came with money, some of which Marie used to help support poor students from Poland. In 1904, Marie gave birth to Eve, the couple’s second daughter. But on April 19, 1906, this happy period came to a tragic end. On a busy street, Pierre Curie was hit by a horse-drawn carriage. He died instantly. Only 39 years old when she was widowed, Marie lost her partner in work and life. Marie struggled to recover from the death of her husband, and to continue his work and teaching. The university offered her her husband’s teaching job. On November 5, 1906, as the first female professor in the Sorbonne’s history, Marie Curie stepped up to the podium and picked up where Pierre had left off. Around her, a new age of science was emerging. A chemistry of the invisible An atom is the smallest particle of an element that still has all the properties of the element. Periodic table creator Dmitri Mendeleev and other scientists had insisted that the atom was the smallest unit in matter. But the English physicist J. J. Thompson, responding to X-ray

UNIT 3—STARS & ELEMENTS TEXT READER 34 research, concluded that certain rays were made up of particles even smaller than atoms. These were subatomic particles. The work of Thompson and Curie contributed to the work of British scientist Ernest Rutherford. In 1899, he found that there were two different kinds of particles coming out of radioactive substances. Radioactivity gave off “beta” rays, which traveled nearly at the speed of light and could penetrate thick barriers, and slower, heavier “alpha” rays. Marie believed radioactivity to be happening inside the atom itself. Rutherford, working with radioactive materials supplied by Marie, researched his “transformation” theory. It claimed that radioactive elements break down. They actually decay into other elements, sending off alpha and beta rays. This theory of decay confirmed Marie’s theory that radioactivity was subatomic. In 1904, Rutherford came up with the term “half-life.” The term refers to the amount of time it takes an unstable element to decay by one-half of its quantity. This would later prove an important discovery for radiometric dating. Scientists realized they could use “half-lives” of elements to measure the age of materials. In 1905, a Swiss physicist, Albert Einstein, was also studying unstable elements. His calculations led him to believe that very small amounts of matter were capable of turning into huge amounts of energy. This idea would lead to his General Theory of Relativity a decade later. Thompson was calling the particles smaller than atoms “electrons,” the first subatomic particles to be identified. Thompson was awarded the 1906 Nobel Prize in Physics in part for the discovery of the electron. In 1911, Rutherford made another breakthrough, building upon Thompson’s earlier theory about the structure of the atom. He outlined a new model for the atom. He fond that it was mostly empty space, with a dense “nucleus” in the center containing “protons.” Marie’s isolation of radium had provided the key that led to these breakthroughs. She had created what she called “a chemistry of the invisible.” The age of nuclear physics had begun. A second Nobel Prize In the years after Pierre’s death, Marie juggled her responsibilities as a single mother, professor, and famous researcher. She wanted to learn more about the elements she discovered and figure out where they fit into Mendeleev’s table of the elements, called the “periodic table.” Elements on the table are arranged by weight. To determine the locations for polonium and radium, she needed to figure out their molecular weight. Her research showed that polonium should be number 84 and radium should be 88. In 1911, Marie was awarded the Nobel Prize for Chemistry, becoming the first person to win two Nobel Prizes.

UNIT 3—STARS & ELEMENTS TEXT READER 35 A year later, Marie was visited by Einstein. The two scientists had much to discuss: What was the source of this immense energy that came from radioactive elements? To promote the study of radioactivity, Marie established the Radium Institute, a research center in Paris and later in Warsaw. Marie Curie’s radioactivity research forever changed the field of medicine. Radium became used to treat cancer. During World War I, she designed radiology cars bringing X-ray machines to hospitals for soldiers wounded in battle. Marie trained women as well as men to be radiologists. In the last two years of the war, more than a million soldiers were X-rayed and many were saved. Her research laid the foundation for the field of radiotherapy, which uses radiation to destroy cancerous tumors in the body. Marie Curie died of leukemia in 1934. We now know that radioactivity caused many of her health problems. In the 1920s, scientists became aware of the dangers of radiation exposure: The energy of the rays speeds through the skin, slams into the molecules of cells, and can harm or even destroy them. A place in the periodic table In 1944, scientists at the University of California–Berkeley discovered a new element, 96, and named it “curium,” in honor of Marie and Pierre. Today we recognize 118 elements. Ninety-two were formed in nature. The others have been created artificially in labs. Marie Curie’s legacy cannot be overstated. Poverty didn’t stop her from pursuing an education. Marriage enhanced her life and career, and motherhood didn’t limit her life’s work. At a time when men dominated science and women didn’t have the right to vote, Marie Curie proved herself a pioneering scientist in chemistry and physics.

Marie Curie: Chemistry, Physics, and Radioactivity (770 L) By Michelle Feder, adapted by Newsela In 1897, Marie Curie began a series of experiments in the science of radioactivity. Her work would change the world of medicine, and give us a better understanding of the atom's structure. Early life and overcoming obstacles Marie Curie became famous for the work she did in Paris. But she was born in Warsaw, Poland, in 1867, as Maria Sklodowska. She was the youngest of five children. Both of her parents were educators: Her father taught math and physics, and her mother ran a private school for girls. But things took a turn for the worse the year she turned 10. Her mother died, and her father lost his job. Her father rented out their bedrooms, and Maria had to sleep on the floor.

UNIT 3—STARS & ELEMENTS TEXT READER 36 Even as a young girl, Maria was interested in science. Her father kept scientific instruments at home in a glass cabinet. The objects fascinated her. Maria proved herself early as an exceptional student. She wanted to continue her education, but the University of Warsaw didn't admit women. Maria knew she would have to leave Poland to keep studying. Maria did not want to leave her family or country, but knew it was necessary. She chose Paris because she wanted to attend the great university there: the University of Paris — the Sorbonne. There she would have the chance to learn from many brilliant thinkers. In Paris When Maria registered at the Sorbonne, she signed her name as “Marie”. She had to work hard to learn French. Of 1,800 students there, only 23 were women. Marie became the first woman to earn a degree in physics from the Sorbonne. In France she met a scientist named Pierre Curie. On July 26, 1895, they were married. They rented a small apartment in Paris, where Pierre worked as a college professor. Marie continued her studies at the Sorbonne. In September 1897, they had a daughter, Irène. Meanwhile, scientists all over the world were making huge discoveries. The year the Curies were married, a German scientist named Wilhelm Roentgen discovered what he called “X- radiation” (X-rays). These rays are electromagnetic radiation and can glow like visible light. Certain chemical materials release them under the right conditions. Roentgen accidentally discovered X-rays in his lab. While experimenting, he saw X-rays glowing through black cardboard he'd placed around a tube filled with gas. Roentgen's breakthrough pushed Marie’s own work forward. Other scientists began experimenting with X-rays. The ability of X-rays to pass through solid materials led to the X-ray machine. It can take a picture of what's inside the human body. While studying X-rays, French physicist Antoine Henri Becquerel found that uranium gave off an entirely new form of ray. It was a narrow, invisible beam of energy. Marie Curie wanted to know why. One of her greatest achievements was solving this mystery. Radiant discoveries Marie Curie, and other scientists of her time, knew that everything in nature is made up of elements. Elements are pure materials such as gold, uranium, and oxygen. They can’t be broken down into other substances, like compounds can. When Marie was born, there were only 63 known elements. Today 118 elements have been identified. At the time she began her work, scientists thought they had found all the elements that existed. But they were wrong. Marie began testing various kinds of natural materials. One substance was a mineral called “pitchblende.” Scientists believed it was made up mainly of oxygen and uranium. But Marie’s tests showed that pitchblende produced much stronger X-rays than those two

UNIT 3—STARS & ELEMENTS TEXT READER 37 elements did alone. She began to think there must be one or more undiscovered elements in pitchblende that made it so powerful. To prove it, she needed loads of pitchblende to run tests on the material. And she needed a lab to test it in. Pierre helped her find an unused shed at the Sorbonne. There, Marie put the pitchblende in huge pots, stirred and cooked it, and ground it into powder. She added chemicals to the substance and tried to separate the elements in it. Every day she mixed a boiling mass with a heavy iron rod nearly as large as herself. After months of this tiring work, Marie and Pierre found what they were looking for. In 1898, Marie discovered a new element. They named it “polonium,” after her native country. Polonium was 400 times more radioactive than any other element. Later that year, the Curies discovered another element. They called it “radium,” from the Latin word for “ray.” It gave off 900 times more radiation than even polonium. Marie also came up with a new term for this property of matter: “radioactive.” It took the Curies four hard years to separate a small amount of radium from the pitchblende. In 1902, the Curies finally could see what they had discovered. Inside the dusty shed, the Curies watched its silvery-blue-green glow. Marie presented her findings to her professors. She suggested that the powerful rays of energy the polonium and radium gave off were actually particles from tiny atoms. The atoms were disintegrating inside the elements and giving off energy. At the time, scientists believed that atoms were solid and unchanging. Marie’s findings went against that widely held belief. The Curies’ research showed that the rays weren’t just energy released from a material’s surface. Instead, the energy was coming from deep within the atoms. This discovery improved our understanding the structure of the atom. A woman of distinction In 1903, Marie received her doctorate degree in physics. It was the first PhD awarded to a woman in France. For their discovery of radioactivity, the couple won the Nobel Prize in physics. Marie Curie was the first woman to receive a Nobel Prize. After many years of hard work and struggle, the Curies had achieved great fame. But there was one serious problem. Both of them suffered from what was later called radiation sickness. Marie coughed and lost weight; they both had severe burns on their hands. They grew tired very quickly. All of this came from handling radioactive material. At the time, scientists didn’t know the dangers of radioactivity. The Nobel gave the couple a better life. Pierre became a professor at the Sorbonne. Marie became a teacher at a women’s college. The Sorbonne still did not allow women professors. The prize came with money, some of which Marie used to help support poor students from Poland.

UNIT 3—STARS & ELEMENTS TEXT READER 38 In 1904, Marie gave birth to Eve, the couple’s second daughter. But on April 19, 1906, this happy period came to a tragic end. On a busy street, Pierre Curie was hit by a horse-drawn carriage. He died instantly. Marie struggled to recover from the death of her husband. The university offered her her husband’s teaching job. On November 5, 1906, she became the first female professor in the Sorbonne’s history. Around her, a new age of science was emerging. A chemistry of the invisible An atom is the smallest particle of an element that still has all the properties of the element. Scientists had believed that the atom was the smallest unit in matter. But the English physicist J. J. Thompson found particles even smaller than atoms — subatomic particles. British scientist Ernest Rutherford built upon this discovery. In 1899, he found that there were two different kinds of particles coming out of radioactive substances. Radioactivity gave off “beta” rays. These rays traveled at nearly the speed of light. They could pass through thick barriers. Radioactive substances also give off slower, heavier “alpha” rays. Rutherford discovered that radioactive elements break down. They actually decay into other elements. In the process, they send out alpha and beta rays. The decay theory confirmed Marie’s theory that radioactivity happens inside that atom itself. In 1904, Rutherford came up with the term “half-life.” The term refers to how long it takes an unstable element to decay to half of its original amount. This discovery would lead to radiometric dating. Scientists realized they could use “half-lives” of elements to measure the age of materials. In 1905, physicist Albert Einstein was also studying unstable elements. His calculations led him to believe that very small amounts of matter were capable of turning into huge amounts of energy. This idea would lead to his General Theory of Relativity a decade later. Thompson called particles smaller than atoms “electrons.” These were the first subatomic particles to be identified. Thompson was awarded the 1906 Nobel Prize in Physics in part for the discovery of the electron. In 1911, Rutherford made another breakthrough about the inside of atoms. He found that they were mostly empty space. But in the center atoms have a dense “nucleus” containing “protons.” Marie’s isolation of radium was the key to Rutherford's breakthrough. She had created what she called “a chemistry of the invisible.” The age of nuclear physics had begun.

UNIT 3—STARS & ELEMENTS TEXT READER 39 A second Nobel Prize In the years after Pierre’s death, Marie juggled her responsibilities as a single mother, professor, and famous researcher. She wanted to learn more about the elements she discovered. And she wanted to figure out where they fit into Mendeleev’s table of the elements, the “periodic table.” Elements on the table are arranged by weight. To determine the locations for polonium and radium, she needed to figure out their molecular weight. Her research showed that polonium should be number 84 and radium should be 88. In 1911, Marie was awarded the Nobel Prize for Chemistry. She was the first person to win two Nobel Prizes. A year later, Marie was visited by Einstein. The two scientists had much to discuss: What was the source of this immense energy that came from radioactive elements? To promote the study of radioactivity, Marie started the Radium Institute, a research center in Paris and Warsaw. Marie Curie’s radioactivity research forever changed the field of medicine. Radium became used in treating cancer. During World War I, she designed radiology cars bringing X-ray machines to hospitals for soldiers wounded in battle. Marie trained women as well as men to be radiologists. In the last two years of the war, more than a million soldiers were X-rayed. Many were saved. Her research laid the foundation for radiotherapy, which uses radiation to destroy cancerous tumors in the body. Marie Curie died of leukemia in 1934. We now know that radioactivity caused many of her health problems. In the 1920s, scientists became aware of the dangers of radiation exposure: The energy of the rays breaks through the skin. Once inside, it slams into the molecules of cells, and can harm or even destroy them. A place in the periodic table In 1944, scientists at the University of California discovered a new element, 96. They named it “curium,” in honor of Marie and Pierre. Today we recognize 118 elements. Ninety-two were formed in nature. The others have been created artificially in labs. Marie Curie’s legacy cannot be overstated. Poverty didn’t stop her from pursuing an education. Marriage enhanced her life and career. Motherhood didn’t limit her life’s work. At a time when men dominated science and women didn’t have the right to vote, Marie Curie proved herself a pioneering scientist in chemistry and physics.

UNIT 3—STARS & ELEMENTS TEXT READER 40 From Alchemy to Chemistry: The Origins of Today's Central Science

Many of the earliest chemists, physicians, and philosophers were also alchemists.

From Alchemy to Chemistry: The Origins of Today's Central Science (1440 L) By Michelle Feder Many of the earliest chemists, doctors, and philosophers also practiced the art of alchemy. The word “alchemy” brings to mind a cauldron full of images: witches hovering over a boiling brew, or perhaps sorcerers in smoky labs or cluttered libraries. Despite these connotations of the mythic and mystical, alchemical practice played an important role in the evolution of modern science. Historically, alchemy refers to both the investigation of nature and an early philosophical and spiritual discipline that combined chemistry with metalwork. Alchemy also encompassed physics, medicine, astrology, mysticism, spiritualism, and art. The goals of alchemy were: . to find the “elixir of life” (it was thought that this magical elixir would bring wealth, health, and immortality); . to find or make a substance called the “philosopher’s stone,” which when heated and combined with “base” (non-precious) metals such as copper and iron, would turn it into gold, thought to be the highest and purest form of matter; and . to discover the relationship of humans to the cosmos and use that understanding to improve the human spirit. Alchemy was scientific but it was also a spiritual tradition. Some of its practitioners had altruistic intentions. For instance, if alchemists could learn the secret of “purifying” base metals into gold, they might gain the ability to purify the human soul. At the same time, alchemy has often been seen as a get-rich-quick scheme and some alchemists were called charlatans and pretenders. But many alchemists were in fact serious-minded practitioners whose work helped lay the groundwork for modern chemistry and medicine. The central science Alchemy began as a quest to know the world around us — its composition as well as our own. That quest for knowledge required an understanding of chemical processes, and while alchemy itself would not survive the Enlightenment (the Age of Reason of the seventeenth

UNIT 3—STARS & ELEMENTS TEXT READER 41 and eighteenth centuries), the quest it began continues today in chemistry. To understand the ever-evolving field of chemistry, which is sometimes called “the central science” because it connects natural sciences like physics, geology, and biology, it’s critical to grasp its beginnings. Alchemists contributed to an incredible diversity of what would later be recognized as chemical industries: basic metallurgy, metalworking, the production of inks, dyes, paints, and cosmetics, leather-tanning, and the preparation of extracts and liquors. It was a fourth-century Indian alchemist who first described the process of zinc production by distillation, a seventeenth-century German alchemist who isolated phosphorus, and another German alchemist of the same period who developed a porcelain material that broke China’s centuries-old monopoly on one of the world’s most valuable commodities. These contributions proved valuable to the societies in which alchemists lived, and to the advancement of civilization. But alchemists often made no distinction between purely chemical questions and the more mystical aspects of their craft. They lacked a common language for their concepts and processes. They borrowed the terms and symbols of biblical and pagan mythology, astrology, and other spiritual arenas, making even the simplest formula read like a magic spell or ritual. And although there were commonly used techniques, alchemists shared no standardized, established scientific practice. Roots in the ancient world The origins of alchemy are difficult to track down. In the East, in India and China, alchemy started sometime before the Common Era (CE) with meditation and medicine designed to purify the spirit and body and to thereby achieve immortality. In the West, alchemy probably evolved from Egyptian metallurgy as far back as the fourth millennium BCE. The ideas of Aristotle (384–322 BCE), who proposed that all matter was composed of the four “elements” — earth, air, fire, and water — began to influence alchemical practices when his student Alexander the Great (356–323 BCE) established Alexandria as a center of learning. Alexander is said by some to have discovered the Greek god Hermes’s famous Emerald Tablet, reputed to contain the secret of the philosopher’s stone, and to have built the Library of Alexandria specifically to house alchemical texts. These texts were, however, almost entirely destroyed in the third century, and soon thereafter the Alexandrian Zosimus wrote what are now the oldest known books on alchemy, which emphasized its mysticism rather than its medical or practical applications. Islamic Arabs took over Alexandria in the seventh century CE, and as the center of learning shifted to Damascus and the newly founded Baghdad, alchemical texts were translated from Greek to Arabic. An eminent figure at that time was Jabir ibn Hayyan (721–815), although some sources say he never existed, who became a royal alchemist in Baghdad. Jabir’s writings were the first to mention such important compounds as corrosive sublimate (mercuric chloride), red oxide of mercury (mercuric oxide), and silver nitrate. Like Aristotle,

UNIT 3—STARS & ELEMENTS TEXT READER 42 Jabir believed metals grew in the Earth, adding to the Aristotelian theory the notion that metals were differentiated by how much mercury and sulfur they contained. Making gold thus required the purification of these ingredients. Scholars in the West first learned about alchemy in roughly the twelfth and thirteenth centuries as they copied and translated Arabic texts into Latin. Medieval science was still dominated by the ideas of Aristotle. Alchemy after the Middle Ages Among the most important of the European alchemists was Paracelsus (1493–1531), a Swiss traveling physician/surgeon and the first toxicologist. Paracelsus believed that the body’s organs worked alchemically, that is, their function was to separate the impure from the pure, and proposed that a balance of three controlling substances (mercury, sulfur, and salt), which he called the “tria prima,” was necessary for maintaining health. Paracelsus treated the plague and other diseases with an alchemical approach that included administering inorganic salts, minerals, and metals. He believed that what he called the “alkahest,” the supposed universal solvent, was the philosopher’s stone, but had no interest in the transmutation of metals, writing, “Many have said of Alchemy, that it is for the making of gold and silver. For me such is not the aim, but to consider only what virtue and power may lie in medicines.” In 1662, Robert Boyle (1627–1691) articulated Boyle’s Law, which states that the volume of a gas decreases as the pressure on it increases, and vice versa. For this and other important contributions to scientific inquiry, Boyle is sometimes called the father of modern chemistry, but he was not a scientist in the current sense of the word. Rather, he is what is called a natural philosopher, someone who studied fundamental questions about nature and the physical Universe before the nineteenth century, when dramatic advances in technology began to revolutionize our understanding of and approach to these questions. Boyle wrote two papers on the transmutation of the elements, claiming to have changed gold into mercury by means of “quicksilver,” the ingredients of which he did not reveal. This caught the attention of Isaac Newton, another enthusiastic alchemist, who, like Boyle, was motivated in his research “by the good it may do in the world.” The two struck up a correspondence. Central to Boyle’s efforts was his “corpuscularian hypothesis.” According to Boyle, all matter consisted of varying arrangements of identical corpuscles. Transforming copper to gold seemed to be just a matter of rearranging the pattern of its corpuscles into that of gold. Boyle used his 1661 text The Sceptical Chymist to explain his hypothesis and to dismiss Aristotle’s four-elements theory, which had persisted through the ages. Boyle recognized that certain substances decompose into other substances (water decomposes into hydrogen and oxygen when it is electrically charged) that cannot themselves be broken down any further. These fundamental substances he labeled elements, which could be identified by experimentation.

UNIT 3—STARS & ELEMENTS TEXT READER 43 Boyle was a prolific experimenter who kept meticulous accounts about both his failures and successes. He was a pioneer of chemical analysis and the scientific method, endlessly repeating his experiments with slight variations to obtain better results and, unheard of among earlier alchemists, always publishing the methods and details of his work in clear terms that could be widely understood. A new framework By the late eighteenth century, the field of chemistry had fully separated from traditional alchemy while remaining focused on questions relating to the composition of matter. Experimentation based on the scientific method, the publication of research results, the search for new elements and compounds and their application in medicine and industry beneficial to all mankind, and other concerns first addressed by alchemists dating back many centuries were now the domain of modern science. Among the most significant of the post-alchemical chemists were the French nobleman Antoine-Laurent Lavoisier (1743–1794) and the Russian chemist Dmitri Mendeleev (1834– 1907). In 1789, Lavoisier wrote the first comprehensive chemistry textbook, and, like Boyle, he is often referred to as the father of modern chemistry. Lavoisier agreed with Boyle that Aristotle’s four-elements theory was mistaken, and in his textbook, he compiled a list of metallic and nonmetallic elements that would point toward the periodic table developed by Mendeleev in 1869. It was Mendeleev who demonstrated that the elements could be arranged in a periodic — regular and recurring — relationship to each other based on their atomic weights, and who created a periodic table that could accurately predict the properties of elements that had yet to be discovered. Mendeleev’s table is still used today. Chemical questions: Our best hope for tomorrow Just as alchemy was a touch point for myriad crafts, creations, and — for its time — cures, chemistry resides in the center of the sciences. As an inquisitive discipline, chemistry touches physics on one side and biology on the other. Chemical questions lead to environmental, industrial, and medical applications. Often working together in research teams at universities and corporations, chemists around the world are developing new techniques and inventions. Like alchemists, sometimes the process of discovery might entail isolating specific components; other findings might come from developing new compounds. Some recent research: University of California–San Francisco biochemists identified a memory-boosting chemical in mice, which might one day be used in humans to improve memory. Cheaper clean-energy technologies could be made possible thanks to a new discovery by a professor of chemistry at Penn State University.

UNIT 3—STARS & ELEMENTS TEXT READER 44 The Duke Cancer Institute found that an osteoporosis drug stopped the growth of breast cancer cells, even in resistant tumors. These are just a few examples of how modern chemistry carries on the alchemical quest for the elixir of life.

From Alchemy to Chemistry: The Origins of Today's Central Science (1180 L) By Michelle Feder, adapted by Newsela Many of the earliest chemists, doctors, and philosophers were also alchemists. The word “alchemy” brings to mind witches hovering over a boiling brew, or perhaps sorcerers in smoky labs or cluttered libraries. Despite these mythic and mystical images, alchemical practice played an important role in the evolution of modern science. Historically, alchemy refers to both the investigation of nature and an early philosophical and spiritual field of study that combined chemistry with metalwork. Alchemy also encompassed physics, medicine, astrology, mysticism, spiritualism, and art. The goals of alchemy were: to find the “elixir of life” (it was thought that this magical elixir would bring wealth, health, and immortality); to find or make a substance called the “philosopher’s stone.” When heated and combined with “base” (non-precious) metals such as copper and iron, it would turn it into gold, thought to be the highest and purest form of matter; and to discover the relationship of humans to the cosmos and use that understanding to improve the human spirit. Alchemy was scientific but it was also a spiritual tradition. Some of its practitioners had good-hearted intentions. For instance, if alchemists could learn the secret of “purifying” copper or iron into gold, they might gain the ability to purify the human soul. At the same time, alchemists were often seen as con artists and fakes. But many alchemists were in fact serious-minded practitioners whose work helped lay the groundwork for modern chemistry and medicine. The central science Alchemy began as a quest to know the world around us. That quest for knowledge required an understanding of chemical processes. Alchemy itself did not survive the Enlightenment (the Age of Reason of the seventeenth and eighteenth centuries). Yet, chemistry continues the quest it began. Chemistry is sometimes called “the central science” because it connects natural sciences like physics, geology, and biology. To understand the ever-evolving field of chemistry, it’s critical to grasp its beginnings.

UNIT 3—STARS & ELEMENTS TEXT READER 45 Alchemists contributed to an incredible diversity of what would later be recognized as chemical industries: basic metallurgy, metalworking, the production of inks, dyes, paints, and cosmetics, leather-tanning, and the preparation of extracts and liquors. It was a fourth-century Indian alchemist who first described the process of zinc production by distillation. In the seventeenth century, a German alchemist isolated phosphorus. Another German alchemist of the same period developed a porcelain material that broke China’s centuries-old monopoly on one of the world’s most valuable products. These contributions proved valuable to the societies in which alchemists lived, and to the advancement of civilization. But alchemists often made no distinction between purely chemical questions and the more mystical aspects of their craft. They lacked a common language for their processes. They borrowed the terms and symbols of biblical and pagan mythology, astrology, and spirituality, making even the simplest formula read like a magic spell or ritual. And although there were commonly used techniques, alchemists shared no standardized, established scientific practice. Roots in the ancient world The origins of alchemy are difficult to track down. In the East, in India and China, alchemy started sometime before the Common Era (CE) with meditation and medicine designed to purify the spirit and body and to thereby achieve immortality. In the West, alchemy probably evolved from Egyptian metallurgy as far back as the fourth millennium BCE. Aristotle (384–322 BCE) proposed that all matter was composed of the four “elements” — earth, air, fire, and water. His ideas began to influence alchemical practices when his student Alexander the Great (356–323 BCE) established Alexandria as a center of learning. Alexander is said by some to have discovered the Greek god Hermes’s famous Emerald Tablet, reputed to contain the secret of the philosopher’s stone. He is said to have built the Library of Alexandria specifically to house alchemical texts. These texts were, however, almost entirely destroyed in the third century. Soon thereafter the Alexandrian Zosimus wrote what are now the oldest known books on alchemy, which emphasized its mysticism rather than its medical or practical applications. Islamic Arabs took over Alexandria in the seventh century CE. They shifted the center of learning to Damascus and the newly founded Baghdad. Alchemical texts were translated from Greek to Arabic. A famous figure of that time was Jabir ibn Hayyan (721–815), who became a royal alchemist in Baghdad. Jabir’s writings were the first to mention such important compounds as mercuric chloride, mercuric oxide, and silver nitrate. Like Aristotle, Jabir believed metals grew in the Earth, adding to Aristotelian theory the notion that metals were differentiated by how much mercury and sulfur they contained. Making gold thus required the purification of these ingredients. Scholars in the West first learned about alchemy in roughly the twelfth and thirteenth centuries as they copied and translated Arabic texts into Latin. Medieval science was still dominated by the ideas of Aristotle.

UNIT 3—STARS & ELEMENTS TEXT READER 46 Alchemy after the Middle Ages Among the most important of the European alchemists was Paracelsus (1493–1531), the first toxicologist, or person to study poisons. Paracelsus believed that the body’s organs worked alchemically, that is, their function was to separate the impure from the pure. He proposed that a balance of three substances (mercury, sulfur, and salt) was necessary for maintaining health. Paracelsus treated the plague and other diseases with an alchemical approach. It included administering inorganic salts, minerals, and metals. He believed that what he called the “alkahest,” the supposed universal solvent, was the philosopher’s stone, but had no interest in the transmutation of metals, writing, “Many have said of Alchemy, that it is for the making of gold and silver. For me such is not the aim, but to consider only what virtue and power may lie in medicines.” In 1662, Robert Boyle (1627–1691) articulated Boyle’s Law. It states that the volume of a gas decreases as the pressure on it increases, and vice versa. For this and other important contributions to scientific inquiry, Boyle is sometimes called the father of modern chemistry. But he was not a scientist in the sense of the word today. Rather, he is what is called a natural philosopher, someone who studied fundamental questions about nature and the physical Universe before the nineteenth century. Afterward, dramatic advances in technology began to revolutionize our understanding of and approach to these questions. Boyle wrote two papers on how elements transmutate, or change form. He claimed to have changed gold into mercury by means of “quicksilver,” the ingredients of which he did not reveal. This caught the attention of Isaac Newton, another enthusiastic alchemist, who, like Boyle, was motivated in his research “by the good it may do in the world.” The two struck up a correspondence. Central to Boyle’s efforts was his “corpuscularian hypothesis.” According to Boyle, all matter consisted of varying arrangements of tiny, identical particles called corpuscles. Transforming copper to gold seemed to be just a matter of rearranging the pattern of its corpuscles into that of gold. Boyle used his 1661 text The Sceptical Chymist to explain his hypothesis and to dismiss Aristotle’s four-elements theory, which had persisted through the ages. Boyle recognized that certain substances decompose into other substances that cannot themselves be broken down any further. For instance, water decomposes into hydrogen and oxygen when it is electrically charged. But hydrogen and oxygen cannot be broken down. These fundamental substances that couldn't be broken down further he called elements. Boyle was a constant experimenter who kept accounts of both his failures and successes. He was a pioneer of chemical analysis and the scientific method. He endlessly repeated his experiments with slight variations to obtain better results. Unheard of among earlier alchemists, he always published the methods and details of his work in clear terms that could be widely understood.

UNIT 3—STARS & ELEMENTS TEXT READER 47 A new framework By the late eighteenth century, the field of chemistry had fully separated from traditional alchemy. At the same time, it remained focused on questions relating to the composition of matter. Experimentation based on the scientific method, the publication of research results, the search for new elements and compounds and their application in medicine and industry to the benefit of all mankind, were concerns first addressed by alchemists dating back many centuries. Now they were the domain of modern science. Among the most significant of the post-alchemical chemists were the French nobleman Antoine-Laurent Lavoisier (1743–1794) and the Russian chemist Dmitri Mendeleev (1834– 1907). In 1789, Lavoisier wrote the first comprehensive chemistry textbook, and, like Boyle, he is often referred to as the father of modern chemistry. Lavoisier agreed with Boyle that Aristotle’s four-elements theory was mistaken, and in his textbook, he compiled a list of metallic and nonmetallic elements that would point toward the periodic table developed by Mendeleev in 1869. It was Mendeleev who demonstrated that the elements could be arranged in a periodic — regular and recurring— relationship to each other based on their atomic weights, and who created a periodic table that could accurately predict the properties of elements that had yet to be discovered. Mendeleev’s table is still used today. Chemical questions: Our best hope for tomorrow Just as alchemy was a touch point for many crafts and cures, chemistry resides in the center of the sciences. As an inquisitive field of study, chemistry touches physics on one side and biology on the other. Chemical questions lead to environmental, industrial, and medical applications. Often working together in research teams at universities and corporations, chemists around the world are developing new techniques and inventions. Like alchemists, sometimes the process of discovery might involve isolating specific components; other findings might come from developing new compounds. Some recent research: University of California–San Francisco biochemists identified a memory-boosting chemical in mice, which might one day be used in humans to improve memory. Cheaper clean-energy technologies could be made possible thanks to a new discovery by a professor of chemistry at Penn State University. The Duke Cancer Institute found that an osteoporosis drug stopped the growth of breast cancer cells, even in resistant tumors. These are just a few examples of how modern chemistry carries on the alchemical quest for the elixir of life.

UNIT 3—STARS & ELEMENTS TEXT READER 48 From Alchemy to Chemistry: The Origins of Today's Central Science (1050 L) By Michelle Feder, adapted by Newsela The word “alchemy” conjures colorful imagery. Think of witches hovering over a boiling brew, or perhaps sorcerers in smoky labs or cluttered libraries. Despite these mythic and mystical images, alchemy played an important role in the evolution of modern science. Historically, alchemy refers to both the investigation of nature and an early philosophical and spiritual field of study that combined chemistry with metalwork. Alchemy also encompassed physics, medicine, astrology, mysticism, spiritualism, and art. The goals of alchemy were: to find the “elixir of life” (it was thought that this magical elixir would bring wealth, health, and eternal life); to find or make a substance called the “philosopher’s stone.” When heated and combined with copper or iron it would turn it into gold, thought to be the highest and purest form of matter; and to discover the relationship of humans to the cosmos and use that understanding to improve the human spirit. Alchemy was scientific but it was also a spiritual tradition. Some of its practitioners had good-hearted intentions. For instance, if alchemists could learn the secret of “purifying” base metals into gold, they might gain the ability to purify the human soul. At the same time, alchemists were often viewed as fakes. But many alchemists were in fact serious-minded practitioners whose work helped lay the groundwork for modern chemistry and medicine. The central science Alchemy began as a quest to know the world around us. That quest for knowledge required an understanding of chemical processes. Alchemy itself did not survive the Enlightenment (the Age of Reason of the seventeenth and eighteenth centuries). Yet, the quest it began continues today in chemistry. Chemistry is sometimes called “the central science” because it connects natural sciences like physics, geology, and biology. To understand where chemistry is going, it’s critical to grasp its beginnings. Alchemists contributed to an incredible number of future chemical industries: basic metallurgy, metalworking, the production of inks, dyes, paints, and cosmetics, leather- tanning, and the preparation of extracts and liquors. It was a fourth-century Indian alchemist who first described the process of zinc production by distillation. In the seventeenth century, a German alchemist isolated phosphorus. Another German alchemist of the same period developed a porcelain material that broke China’s centuries-old monopoly on one of the world’s most valuable products. These contributions proved valuable to the societies in which alchemists lived. And they advanced civilization.

UNIT 3—STARS & ELEMENTS TEXT READER 49 But alchemists often made no distinction between purely chemical questions and the more mystical aspects of their craft. They lacked a common language for their concepts and processes. They borrowed the terms and symbols of biblical and pagan mythology, astrology, and other spiritual arenas. Even the simplest formula read like a magic spell or ritual. And although there were commonly used techniques, alchemists shared no standardized scientific practice. Roots in the ancient world The origins of alchemy are difficult to track down. In the East, in India and China, alchemy started sometime before the Common Era (CE). They began with meditation and medicine designed to purify the spirit and body and to thereby achieve immortality. In the West, alchemy probably evolved from Egyptian metallurgy as far back as the fourth millennium BCE. Aristotle (384–322 BCE) proposed that all matter was composed of the four “elements” — earth, air, fire, and water. His ideas began to influence alchemical practices when his student Alexander the Great (356–323 BCE) established Alexandria in Egypt as a center of learning. Alexander is said by some to have discovered the Greek god Hermes’s famous Emerald Tablet, reputed to contain the secret of the philosopher’s stone. He is said to have built the Library of Alexandria specifically to house alchemical texts. These texts were, however, almost entirely destroyed in the third century. Soon thereafter the Alexandrian Zosimus wrote the first books on alchemy. They emphasized its mysticism rather than its medical or practical uses. Islamic Arabs took over Alexandria in the seventh century CE. They shifted the center of learning to Damascus and the newly founded Baghdad. Alchemical texts were translated from Greek to Arabic. A famous figure of that time was Jabir ibn Hayyan (721–815), a royal alchemist in Baghdad. Jabir’s writings were the first to mention such important compounds as mercuric chloride, mercuric oxide, and silver nitrate. Like Aristotle, Jabir believed metals grew in the Earth. Jabr built on Aristotle's theory with his own idea that metals were different by how much mercury and sulfur they contained. Making gold thus required the purification of these two ingredients. Scholars in the West first learned about alchemy in roughly the twelfth and thirteenth centuries as they copied and translated Arabic texts into Latin. Medieval science In Europe was still dominated by the ideas of Aristotle. Alchemy after the Middle Ages Among the most important of the European alchemists was Paracelsus (1493–1531). He was the first toxicologist, a scientist who studies poisons. Paracelsus believed that the body’s organs worked alchemically, that is, their function was to separate the impure from the pure.

UNIT 3—STARS & ELEMENTS TEXT READER 50 He proposed that a balance of three substances (mercury, sulfur, and salt) was necessary for maintaining health. Paracelsus treated the plague and other diseases with an alchemical approach. It included administering salts, minerals, and metals. He believed that what he called the “alkahest,” the supposed universal solvent, was the philosopher’s stone. But he but had no interest in metals, writing, “Many have said of Alchemy, that it is for the making of gold and silver. For me such is not the aim, but to consider only what virtue and power may lie in medicines.” In 1662, Robert Boyle (1627–1691) came up with what we now call Boyle’s Law. It states that the volume of a gas decreases as the pressure on it increases, and vice versa. For this and other important contributions to science, Boyle is sometimes called the father of modern chemistry. But he was not a scientist in the current sense of the word. Rather, he is what is called a natural philosopher, someone who studied fundamental questions about nature and the physical Universe before the nineteenth century. After his time, dramatic advances in technology began to revolutionize our understanding of and approach to these questions. Boyle wrote two papers on the transmutation of the elements. He claimed to have changed gold into mercury by means of “quicksilver,” the ingredients of which he did not reveal. This caught the attention of Isaac Newton, another enthusiastic alchemist, who, like Boyle, was motivated in his research “by the good it may do in the world.” The two struck up a correspondence. Central to Boyle’s efforts was his “corpuscularian hypothesis.” According to Boyle, all matter consisted of varying arrangements of identical corpuscles, or tiny particles. Transforming copper to gold seemed to be just a matter of rearranging the pattern of its corpuscles into that of gold. Boyle used a 1661 book to explain his hypothesis and to dismiss Aristotle’s four-elements theory, which had survived through the ages. Boyle recognized that certain substances decompose into other substances that cannot themselves be broken down any further. For instance, water decomposes into hydrogen and oxygen when it is electrically charged. But hydrogen and oxygen couldn't be broken down. These fundamental substances that couldn't be broken down further he labeled elements. Boyle was a constant experimenter who kept accounts of both his failures and successes. He was a pioneer of chemical analysis and the scientific method. He endlessly repeated his experiments with slight variations to obtain better results. Unheard of among earlier alchemists, he always published the methods and details of his work in clear terms that could be widely understood. A new framework By the late eighteenth century, the field of chemistry had fully separated from traditional alchemy. At the same time, it remained focused on questions relating to the composition of

UNIT 3—STARS & ELEMENTS TEXT READER 51 matter. Experimentation based on the scientific method, the publication of research results, the search for new elements and compounds and their application in medicine and industry to benefit all mankind, were all concerns first addressed by alchemists. Now they were the domain of modern science. Among the most significant of the post-alchemical chemists were the French nobleman Antoine-Laurent Lavoisier (1743–1794) and the Russian chemist Dmitri Mendeleev (1834– 1907). In 1789, Lavoisier wrote the first comprehensive chemistry textbook. Like Boyle, he is often referred to as the father of modern chemistry. Lavoisier agreed with Boyle that Aristotle’s four-elements theory was mistaken. In his textbook, he compiled a list of metallic and nonmetallic elements. It was Mendeleev who would take that list and put it into the periodic table he developed in 1869. Mendeleev demonstrated that the elements could be arranged in a periodic — regular and recurring — relationship to each other based on their atomic weights. And it was he who created a periodic table that could accurately predict the properties of elements that had yet to be discovered. Mendeleev’s table is still used today. Chemical questions: Our best hope for tomorrow Just as alchemy was a touch point for many crafts, inventions and cures, chemistry resides in the center of the sciences. As an inquisitive field of study, chemistry touches physics on one side and biology on the other. Chemical questions lead to environmental, industrial, and medical uses. Often working together in research teams at universities and companies, chemists around the world are developing new techniques and inventions. Like alchemists, sometimes the process of discovery might involve isolating specific components; other findings might come from developing new compounds. Some recent research: University of California–San Francisco biochemists identified a memory-boosting chemical in mice. One day it may be used in humans to improve memory. Cheaper clean-energy technologies could be made possible thanks to a new discovery by a chemistry professor at Penn State University. The Duke Cancer Institute found that an osteoporosis drug, meant to prevent the weakening of bones, actually stopped the growth of breast cancer cells. It even worked in resistant tumors. These are just a few examples of how modern chemistry carries on the alchemical quest for the elixir of life.

UNIT 3—STARS & ELEMENTS TEXT READER 52 From Alchemy to Chemistry: The Origins of Today's Central Science (960L) By Michelle Feder, adapted by Newsela The word “alchemy” brings to mind colorful imagery. Think of witches hovering over a boiling brew. Or, perhaps sorcerers in smoky labs or dusty libraries. Despite these mystical images, alchemy played an important role in the evolution of modern science. Alchemy was an early philosophical and spiritual field of study that combined chemistry with metalwork. But it was also an investigation of nature. Alchemy included physics, medicine, astrology, mysticism, spiritualism, and art. The goals of alchemy were: to find the “elixir of life” (it was thought that this magical elixir would bring wealth, health, and eternal life); to find or make a substance called the “philosopher’s stone.” When heated and combined with copper or iron it would turn it into gold, thought to be the highest and purest form of matter; and to discover the relationship of humans to the cosmos and use that understanding to improve the human spirit. Alchemy was scientific, but it was also spiritual. Some of its practitioners had good hearts. For instance, if alchemists could learn the secret of “purifying” copper or iron into gold, they might gain the ability to purify the human soul. At the same time, many alchemists were viewed as con artists and fakes. But many alchemists were in fact serious-minded practitioners. Their work helped lay the foundation for modern chemistry and medicine. The central science Alchemy began as a quest to know the world around us. That quest for knowledge required an understanding of how chemicals worked. Alchemy itself died out during eighteenth century with the rise of modern science. Yet, the quest it began continues today in chemistry. Chemistry is sometimes called “the central science” because it connects sciences like physics, geology, and biology. To understand the field of chemistry, we must grasp its beginnings. Alchemists contributed to an incredible number of future uses of chemicals: metalworking, inks, paints, and cosmetics, and the preparation of extracts and liquors. It was alchemists who first figured out how to isolate zinc and phosphorus. A German alchemist developed a porcelain material. It's creation broke China’s centuries-old control over one of the world’s most valuable products. These contributions proved valuable to the societies in which alchemists lived. And they advanced civilization.

UNIT 3—STARS & ELEMENTS TEXT READER 53 But alchemists often made no separation between their work with chemicals and what we might call magic. They borrowed symbols and words from the Bible and myths. Even the simplest formula read like a magic spell or ritual. And although there were commonly used techniques, alchemists shared no standardized scientific practice. Roots in the ancient world The origins of alchemy are difficult to track down. In the East, in India and China, alchemy started sometime before the Common Era (CE). They began with meditation and medicine designed to purify the spirit and body and to thereby achieve immortality. In the West, alchemy probably evolved from Egyptian metallurgy as far back as the fourth millennium BCE. Aristotle (384–322 BCE) believed all matter was made of the four “elements” — earth, air, fire, and water. His ideas began to influence alchemy when his student Alexander the Great (356–323 BCE) established Alexandria in Egypt as a center of learning. Alexander is said by some to have discovered the Greek god Hermes’s famous Emerald Tablet. reputed to contain the secret of the philosopher’s stone. Islamic Arabs took over Alexandria in the seventh century CE. They shifted the center of learning to Damascus and the newly founded Baghdad. Alchemical texts were translated from Greek to Arabic. A famous figure of that time was Jabir ibn Hayyan (721–815), a royal alchemist in Baghdad. Jabir’s writings were the first to mention important metallic compounds. Like Aristotle, Jabir believed metals grew in the Earth. But Jabr came up with something new. He believed that the key to the differences between metals was how much mercury and sulfur they contained. Making gold thus required the purification of these two ingredients. Scholars in the West first learned about alchemy in roughly the twelfth and thirteenth centuries as they copied and translated Arabic texts into Latin. Medieval science was still dominated by the ideas of Aristotle. Alchemy after the Middle Ages Among the most important of the European alchemists was Paracelsus (1493–1531). He was the first toxicologist, a person who studies poisons. Paracelsus believed that the body’s organs worked alchemically. That is, their function was to separate the impure from the pure. He proposed that a balance of three substances (mercury, sulfur, and salt) was necessary for maintaining health. Paracelsus treated the plague and other diseases with an alchemical approach. It included administering inorganic salts, minerals, and metals. He believed that what he called the “alkahest,” the supposed universal solvent, was the philosopher’s stone. But he had no interest in metals, writing, “Many have said of Alchemy, that it is for the making of gold and silver. For me such is not the aim, but to consider only what virtue and power may lie in medicines.”

UNIT 3—STARS & ELEMENTS TEXT READER 54 In 1662, Robert Boyle (1627–1691) came up with what we call Boyle’s Law. It states that the volume of a gas decreases as the pressure on it increases — and vice versa. For this discovery and others, Boyle is sometimes called the father of modern chemistry. But he was not a scientist as we think of them. Rather, he was a natural philosopher, someone who studied fundamental questions about nature and the universe before the nineteenth century. After his time, dramatic advances in technology began to revolutionize how we approached these questions. Boyle studied the transmutation of the elements. He claimed to have changed gold into mercury by means of “quicksilver,” the ingredients of which he did not reveal. This caught the attention of Isaac Newton, another enthusiastic alchemist. Like Boyle, he was motivated in his research “by the good it may do in the world.” The two struck up a correspondence. Central to Boyle’s efforts was his “corpuscularian hypothesis.” Boyle believed that all matter consisted of arrangements of tiny identical particles called corpuscles. Transforming copper to gold seemed to be just a matter of rearranging the pattern of its corpuscles into that of gold. Aristotle’s four-elements theory was still around. Boyle sought to overthrow it. Boyle recognized that certain substances decompose into other substances. At some point though there are substances that cannot be broken down any further. For instance, water decomposes into hydrogen and oxygen when it is shot through with electricity. But hydrogen and oxygen can't be broken into anything smaller. These fundamental substances that couldn't be broken down further he called elements. Boyle was a constant experimenter who kept accounts of both his failures and successes. He was a pioneer of the scientific method. He endlessly repeated his experiments with slight variations to obtain better results. Unheard of among earlier alchemists, he always published the methods and details of his work in clear terms that could be widely understood. A new framework By the late eighteenth century, the field of chemistry had fully separated from traditional alchemy. Yet chemistry sought to tackle the same questions alchemy once did. Experimentation based on the scientific method, the publication of research results, the search for new elements and compounds and their application in medicine to help mankind, were all concerns first addressed by alchemists. Now they were part of modern science. Among the most significant of the post-alchemical chemists were the Frenchman Antoine- Laurent Lavoisier (1743–1794) and Russian chemist Dmitri Mendeleev (1834–1907). In 1789, Lavoisier wrote the first true chemistry textbook. Like Boyle, he is often referred to as the father of modern chemistry. Lavoisier agreed with Boyle that Aristotle’s four-elements theory was wrong. In his textbook, he made a list of metallic and nonmetallic elements.

UNIT 3—STARS & ELEMENTS TEXT READER 55 It was Mendeleev who would organize all those elements into the periodic table. In 1869, he showed that the elements could be arranged in a periodic — regular and recurring — relationship to each other based on their atomic weights. His periodic table also could accurately predict the properties of elements that had yet to be discovered. Mendeleev’s table is still used today. Chemical questions: Our best hope for tomorrow Just as alchemy was a touch point for many crafts, chemistry is at the center of the sciences. It's a field of study that looks for answers to big questions. Chemists around the world are developing new techniques and inventions. Like alchemists, sometimes they isolate or purify specific components. Other findings might come from developing new compounds. Some recent research: • University of California–San Francisco biochemists identified a memory-boosting chemical in mice. One day it may be used in humans to improve memory. • Cheaper clean-energy technologies could be made possible thanks to a new discovery by a chemistry professor at Penn State University. • The Duke Cancer Institute found that an osteoporosis drug, meant to prevent the weakening of bones, actually stopped the growth of breast cancer cells. It even worked in resistant tumors. These are just a few examples of how modern chemistry carries on the alchemical quest for the elixir of life.

From Alchemy to Chemistry: The Origins of Today's Central Science (810L) By Michelle Feder, adapted by Newsela Many of the first chemists, doctors, and philosophers were also alchemists. The word “alchemy” brings to mind witches stirring a boiling pot, or sorcerers in smoky labs. Despite these magical images, alchemy led to how science is practiced today. Alchemy was an early philosophical and spiritual field of study. It combined chemistry with metalwork. But it also explored how nature works. Alchemy brought together physics, medicine, astrology, mysticism, spiritualism, and art. The goals of alchemy were: to find the “elixir of life.” It was thought that this magical potion would bring wealth, health, and eternal life;

UNIT 3—STARS & ELEMENTS TEXT READER 56 to find or make a substance called the “philosopher’s stone.” Alchemists thought gold was the purest form of matter. They believed if they combined the "stone" with copper or iron it would create gold; and to discover the relationship of humans to the cosmos. With that knowledge, alchemists wanted to improve the human spirit. Alchemy was scientific, but it was also spiritual. Some who practiced it had good hearts. Alchemists wanted to learn the secret of “purifying” copper or iron into gold. If they could accomplish this, they thought they might be able to purify the human soul. At the same time, alchemists were often seen as fakes. But many alchemists were in fact serious about their work. What they accomplished helped lay the building blocks for modern chemistry and medicine. The central science Alchemy began as a quest to know the world around us. That quest for knowledge required an understanding of how chemicals worked. Alchemy itself died out during the 1700s with the rise of modern science. Yet, the quest it began continues today in chemistry. Chemistry is sometimes called “the central science.” It connects sciences like physics, geology, and biology. To understand the field of chemistry, we must start at the beginning. Alchemists contributed to many future uses of chemicals like metalwork, paints and cosmetics. These contributions enriched the societies in which alchemists lived. They even helped advance civilization. But alchemists often saw no difference between their work with chemicals and what we might call magic. They borrowed symbols and words from the Bible and myths. Even the simplest formula read like a magic spell. And although there were commonly used practices, alchemists had no standards that they all used. Roots in the ancient world The origins of alchemy are difficult to track down. In India and China, alchemy started sometime before the Common Era (CE). It began with meditation and medicine designed to purify the spirit and body. Its goal was to achieve immortality, or eternal life. In the West, alchemy probably evolved from Egyptian metalworking as far back as 4000 BCE. Greek thinker Aristotle (384–322 BCE) believed all matter was made of four “elements.” He thought that earth, air, fire, and water were the essential parts of all things. These ideas influenced alchemy. His student Alexander the Great (356–323 BCE) established the city of Alexandria in Egypt as a great center of learning. The field of alchemy advanced in Alexandria. Islamic Arabs took over Alexandria in the seventh century CE. They shifted the center of learning to Baghdad. Alchemical books were translated from Greek to Arabic. A famous

UNIT 3—STARS & ELEMENTS TEXT READER 57 figure of that time was Jabir ibn Hayyan (721–815), a royal alchemist in Baghdad. Jabir’s writings were the first to mention compounds made of metals. Like Aristotle, Jabir believed metals grew in the Earth. But Jabr came up with something new. He thought that the key to the differences between metals was how much mercury and sulfur they contained. If those two ingredients could be purified, Jabr thought gold could be made. Scholars in Europe first learned about alchemy in roughly the 1100s and 1200s. They translated Arabic texts on alchemy into Latin and learned from them. Science in Europe during Medieval times was still dominated by the ideas of Aristotle. Alchemy after the Middle Ages Among the most important of the European alchemists was Paracelsus (1493–1531). He was the first toxicologist, a person who studies poisons. Paracelsus believed that the body’s organs worked alchemically. That is, their function was to separate the impure from the pure. He proposed that a balance of three substances (mercury, sulfur, and salt) was necessary for maintaining health. Paracelsus treated the plague and other diseases with alchemy. He gave salts, minerals, and metals to patients. But he had no interest in metals, writing, “Many have said of Alchemy, that it is for the making of gold and silver. For me such is not the aim, but to consider only what virtue and power may lie in medicines.” In 1662, Robert Boyle (1627–1691) came up with what we call Boyle’s Law. It states that the volume of a gas decreases as the pressure on it increases — and vice versa. For this discovery and others, Boyle is sometimes called the father of modern chemistry. But he was not a scientist as we think of them. Rather, he was a natural philosopher. These early scientists studied nature and the Universe. But their approach wasn't truly scientific. After the period of the natural philosophers, advances in technology changed everything. They revolutionized how scientists investigated questions about nature and led to modern science. Boyle studied how elements changed forms. He claimed to have changed gold into mercury by means of “quicksilver.” But, he didn't reveal the ingredients of his concoction. Boyle's work caught the attention of Isaac Newton, another enthusiastic alchemist. Like Boyle, he was motivated in his research “by the good it may do in the world.” At the center of Boyle’s efforts was his “corpuscularian hypothesis.” Boyle believed that all matter consisted of arrangements of corpuscles. These were tiny, identical particles. Transforming copper to gold seemed to be just a matter of rearranging the pattern of its corpuscles. Then, presto, you'd have gold. Aristotle’s four-elements theory was still being used. Boyle wanted to put an end to that. He studied how certain substances decompose, or fall apart. He noticed that some decompose into other substances. At some point though, there are substances that cannot be broken down

UNIT 3—STARS & ELEMENTS TEXT READER 58 any further. For instance, if you shoot electricity through water it decomposes into hydrogen and oxygen. But hydrogen and oxygen can't be broken into anything smaller. Fundamental substances that can't be broken down further he called elements. Boyle was a constant experimenter. He kept accounts of both his failures and successes. Boyle pioneered the scientific method, a way of making observations and doing experiments. He endlessly repeated experiments. He would vary them slightly to achieve better results. Boyle always published the details of his work in terms that could be widely understood. This was unheard of among earlier alchemists. A new framework By the late 1700s, the field of chemistry had separated from alchemy. Yet chemistry was trying to answer the same questions alchemy once did. Early alchemists were the first to experiment based on the scientific method and publish their research. They began the search for new elements and compounds. And they tried to apply their findings to medicine to help mankind. Now modern science was doing all of these things. Among the most significant of the post-alchemical chemists were the Frenchman Antoine- Laurent Lavoisier (1743–1794) and Russian chemist Dmitri Mendeleev (1834–1907). In 1789, Lavoisier wrote the first true chemistry textbook. Like Boyle, he is often called the father of modern chemistry. Lavoisier agreed with Boyle that Aristotle’s four-elements theory was wrong. In his textbook, he made a list of elements. Then Mendeleev came along. He organized those elements into the periodic table. In 1869, he showed that the elements could be arranged in relationship to each other based on their atomic weights. His periodic table also predicted the properties of elements that hadn't even been discovered. Mendeleev’s table is still used today. Chemical questions: Our best hope for tomorrow Just as alchemy touched on many crafts, chemistry is at the center of the sciences. It's a field of study that looks for answers to big questions. Chemists around the world are developing new techniques and inventions. Like alchemists, sometimes they separate or purify substances. They also develop new compounds. Some recent research: University of California biochemists found a memory-boosting chemical in mice. One day it may be used in humans to improve memory. Clean-energy could be made cheaper thanks to a new discovery by a chemistry professor at Penn State University.

UNIT 3—STARS & ELEMENTS TEXT READER 59 The Duke Cancer Institute found that a drug meant to prevent the weakening of bones actually stopped the growth of breast cancer cells. It even works in tumors that have resisted treatment. These are just a few examples of how modern chemistry carries on the alchemical quest for the elixir of life.

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