<<

: Heralding its latest member

Scientists in Russia have just created a new element, adding to the ever- growing periodic table. This lesson will take you back in time, exploring the periodic table from it’s conception to its current day form. You will investigate the following: • How is organising the elements into the periodic table helpful? • How are electrons arranged into energy levels? • What links atomic structure and the periodic table together? • Where do get their colours from? So get your energy levels ready for some electron excitation!

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com Introduction: Periodic table (P1)

The periodic table at the back of your textbook may be outdated – scientists in Russia have created a new element.

The position of an element on the periodic table is determined by how many it has in its nucleus. With 117, the new element – dubbed ununseptium but also known simply as element 117 – is the heaviest confirmed so far, sitting at the far end of the periodic table.

Element 117 was made by fusing together nuclei of two containing 20 and 97 protons respectively. This process is not unlike throwing two snowballs together and hoping they’ll stick to form a larger snowball – it’s not easy. And the larger atoms get, the more likely they are to decay because their numerous protons push each other out of the nucleus.

Atoms of the same element always have the same number of protons, but they can possess different numbers of neutrons. These different forms are called . Scientists think that the varying ratio of neutrons to protons makes some isotopes more stable than others.

Unfortunately, element 117 fell apart milliseconds after it was formed. Still, scientists hope that its creation will teach them how atoms stick together – and what makes them fall apart.

Read or listen to the full Cosmos magazine article here. Credit: iStock

Question 1

Describe: The term periodic means "shows a repeating pattern". One example of something periodic is the seasons – summer is always followed by autumn, winter and spring, then back to summer. List three other things that are periodic.

Credit: Boing Boing Video / YouTube.

The elements Every naturally occurring in the universe was created either in the , 14 billion years ago, or in a . The Big Bang produced the lightest elements: and , and some and . The rest of the helium, lithium and beryllium, and all of the other elements (with one or two exceptions not found in nature) up to number 92, , were formed in .

Stars begin as mostly hydrogen. The immense force of the star's gravity fuses hydrogen into helium, releasing vast amounts of energy. When the hydrogen runs out the star starts to die. The other, heavier, elements are now formed up until, as a supernova, the star explodes sending the out into space, where some of it forms planets.

Atoms consist of a central nucleus of protons and neutrons, with minute electrons flying around. Elements are substances made up of atoms with the same number of protons, also known as the element's . Compounds are substances where atoms of different elements are chemically bound to one another.

All the elements from number 93, , have been created artificially. They are all radioactive, meaning that when they are left alone the atoms split into lighter elements. There are claims that element numbers 113, 115 and 118 have been created, but these are still waiting for official confirmation, like that recently given for element 117. Question 1

State: Uncharged atoms have the same number of electrons as protons. How many electrons are there in an uncharged atom of element 117?

The element has an atomic number of 6 since it has 6 protons. Its most common has a mass number of 12 since it has 6 neutrons in addition to the 6 protons. The atomic number and mass number are often indicated on periodic tables. Examine the example of carbon below before answering Question 2.

Did you know?

The mass number of an atom is a count of the total number of protons and neutrons in its nucleus, whereas its is the mean mass of all of the naturally occurring isotopes of the element taking into account their relative abundances.

Left: Periodic tables often include the atomic number and mass number of each element. Right: Graphite and diamonds are two different forms of carbon. Credit: Universal History Archive / UIG / Getty Images and Fabrice Coffrini / AFP / Getty Images

Question 2

Find: Determine the atomic number, number of protons, number of electrons, mass number and number of neutrons for each of the following elements: Element Atomic number Number of protons Number of Mass number Number of electrons neutrons 6 6 6 12 6

Periodic table Amazingly, when 19th-century Russian chemistry professor created the version of the periodic table that we use today, the atom itself hadn't even been discovered. He knew nothing about protons or atomic numbers.

Mendeleev compared all the elements to hydrogen, sorted them by their relative weights and organised them into family groups with similar properties. His understanding of these family groups was so strong that he was able to leave gaps for, as yet, undiscovered elements and make predictions about their properties. Mendeleev lived long enough to see other scientists discover three elements for which he had left gaps – , and . His predictions about the properties of these elements turned out to be perfectly accurate. Loading...

Question 3

Recall: The first element to be discovered was

hydrogen.

helium.

Question 4

Identify: Why were some elements easier to discover than others?

The periodic table is a method of arranging the elements, using atomic number as the main organising property. The horizontal rows are known as periods, whereas the vertical columns are known as groups. The organisation of the table allows us to observe a repeating pattern of properties for the groups.

Specific names have been given to the chemical family groupings of elements to describe some of their properties. Examine this periodic table before answering the following two questions. Question 5

Label: Add the following terms to the periodic table below:

; ; non-metals

Question 6

Label: Add the following terms to the periodic table below:

alkali metals; alkaline metals; transition metals; post transition metals; other non-metals; ; noble ; lanthanoids; actinoids Question 7

Locate: The Introduction section describes the discovery of a new element, number 117, temporarily known as ununseptium (Uus). Which does element 117 belong to?

Question 8

Describe: Ununseptium, (Uus) was produced by colliding the atoms -48 (48Ca) and -249 (249Bk) together. Write the reaction as a chemical equation.

Hint: Use the "Text" to write your equation. You will need to use the "Superscript" to add the mass numbers and the "Add math" button to add the equation arrow.

Credit: iStock

Electron configuration The (sometimes known as ) of an atom refers to the arrangement of its electrons in energy levels surrounding the nucleus. Electron configuration is the structural feature of atoms that determines the chemical properties of an element.

More specifically, it is the number of electrons (electrons located in the highest energy level of an atom) that determines:

the group on the periodic table in which the element is located whether the atom is metallic, non-metallic or its chemical properties and therefore how it will chemically interact with other atoms the combining ratio between atoms (i.e. whether it bonds with another atom in a 1:1 or 1:2 or 2:3 ratio etc.)

The remainder of this lesson focuses on the how the electron configuration of an atom determines its position in the periodic table. Loading...

Note: The method of arranging electrons described in the video clip works for elements 1-18. For elements with atomic numbers greater than 18 a more complex method of writing electron configurations is needed, which you will learn about in senior Chemistry classes.

To summarise the video, you can deduce which and group an element belongs to from its electron configuration, and vice versa. For example, the elements (2,8,1) and (2,8,7) are both in the third period because their electronic configurations have three numbers. However, sodium is in group 1 and chlorine is in group 17. This information is represented in the table below.

Number of protons Element name Number of electrons Simple electron Period Group configuration 11 Sodium 11 2, 8, 1 3 1 17 Chlorine 17 2, 8, 7 3 17 Question 1

Organise: Add electrons (as green circles) to the following energy level diagrams and name each element.

a) b)

Question 2

Summarise: Complete the following table for elements in Question 1 above.

Number of protons Number of electrons Simple electron configuration Period Group a) b) Question 3

Deduce: Using your understanding of electron configuration and how it determines an element's position in the periodic table, deduce the electron configurations for the elements with outlines. You may use a periodic table to assist you, but it is not necessary.

One element has been completed for you. The element in period 3, group 1 is element number 11 (sodium). This element will have 11 electrons organised into three energy levels, with only 1 . The electrons are arranged in a 2, 8, 1 configuration.

Question 4

Analyse: Given the following simple electron configurations, use a periodic table to determine the symbols and names of the elements represented.

Electron configuration Element symbol Element name 2,1 2,7 2,8,4

Question 5

Select: The University of Nottingham, UK has produced short video clips about each of the known elements, including element number 117.

Access the periodicvideos.com website and select an element that you are not familiar with. Name your chosen element and, after having watched the video clip, report three of the element's properties that you did not previously know. For best results when printing activities, enable your web browser to print background colours and images. Apply: Periodic table (P2)

Experiment: Investigating flame colours of salts

Background You have learned that each of the more than 110 elements has distinct properties and a characteristic atomic structure composed of protons, neutrons and electrons. You have also learned that the electrons in an atom occupy different, and very specific, energy levels, which can be represented using electron configurations.

When all of the electrons in an atom are at their lowest possible energy level, and positioned closest to the nucleus, they are said to be in their ground state configuration.

However, the valence electrons in a metal atom are held so loosely by the atom’s positively charged nucleus that they can be excited by the heat in a Bunsen burner flame. This causes them to travel away from the nucleus and move up to higher energy levels, increasing their potential energy. When an electron is in a higher energy shell than its ground state configuration, it is said to be in an excited state.

At a higher energy level an excited electron is very unstable and so will naturally return to its ground state configuration, so as to be stable again. As the electron returns to its original energy level it releases light energy. For most group 1 and 2 metal elements the wavelength of the emitted light, produced when an excited electron returns to its ground state, is within the visible part of the electromagnetic spectrum. This means that we can see it as one of the colours of the rainbow.

The exact colour (wavelength) of light produced in this way is characteristic for each element, which makes the a useful qualitative method in chemistry for determining the identity or possible identity of the metal element in a compound. Colours differ because each type of element has different spacings between its energy levels.

The colours produced by metal atoms are utilised by firework manufacturers. By including different metal salts, or of metal salts, in the exploding shells of their fireworks, these artists can produce beautiful displays in nearly all the colours of the rainbow.

Credit: iStock

Aim To investigate the flame colours produced by a range of metal compounds and then use your results to determine which metal salt is present in a common household chemical.

Materials Test tube racks for small test tubes Bench mats Bunsen burners Small test tubes, labelled with names of metal salts and hazard warnings Wooden splints, pre-soaked in distilled and then placed into relevant metal salt solutions Small test tubes, labelled with distilled water Approximately 0.5 M solutions of some or all of the following: chloride (Low hazard) Lithium chloride (Harmful) (Low hazard) chloride (Low hazard) chloride (Low hazard) (Irritant) chloride (Irritant) (II) chloride (Harmful, Danger to the environment)

Common household chemical - cream of tartar

Procedure 1. Tie back long hair and put on safety glasses and lab coats. 2. Note how many different flame test ‘stations’ are set up around the classroom. 3. Prepare a qualitative data table for your results – you will be recording the name of each metal salt solution and your observations during the flame tests. 4. Perform your first flame test by placing the wooden splint (soaked in the metal salt solution) into the coolest part of the Bunsen burner flame then slowly moving it into the hottest part of the flame for 2 seconds. Be sure not to burn the wooden splint. 5. Immediately after viewing the flame colour, cool the wooden splint by placing it into the test tube of water. 6. Replace the cooled wooden splint into its original salt solution. 7. Record the name of the metal salt solution tested and your observations. Try to be as descriptive as possible with your observations – for example, a metal salt solution that produces a red flame may be more accurately described as ‘brick red’ or ‘ engine red’. 8. Perform the remaining flame tests around the classroom, recording your results as you go along. 9. One of the ‘stations’ will be set up with a solution of the common household chemical, cream of tartar; perform the flame test for this solution in exactly the same way as the others. 10. Clean up following your teacher’s instructions.

Safety Information a lab coat and safety glasses at all times. If you have long hair make sure to tie it back. Be cautious around the Bunsen burner. Some of the chemicals being tested are hazardous – you should follow the teacher’s instructions about handling of these chemicals.

Variables Independent variable – type of metal salt solution

Dependent variable – colour produced when metal salt solution is placed into Bunsen burner flame

Note: The independent variable is what is being changed each time, the dependent variable is what you are measuring or testing

Hypothesis It is possible that atoms of different metal elements produce different colours when placed into the Bunsen burner flame because each element has a unique number of protons and therefore a unique electron configuration. Question 1

Results

Collect: Use the project space below to present your results. You should construct a table of results but you may also include photos, video or other representations.

Discussion

Question 2 Question 3

Justify: Explain why a different wooden splint was used for each Assess: Identify the metal element present in the common metal salt solution household chemical, cream of tartar, using your results to support your answer.

Question 4

Apply: Using a periodic table, state the group and period numbers of the metal element you identified in the common household chemical, cream of tartar and, in your own words, explain what these numbers mean.

Question 5 Question 6

Evaluate: Identify some limitations to the experimental design Evaluate: Suggest changes that you could make if you were to that prevent you from collecting more reliable and accurate repeat this experiment, which address the limitations you data. identified. Question 7

Conclusion

Conclude: Write a concluding statement that addresses the aim of the experiment and the hypothesis.

Julia Abbott always keeps a periodic table with her in her wallet. “You never know when you might need to know the relative atomic mass of element 72,” she jokes. (“It’s , 178.49!”)

Julia’s love for the periodic table doesn’t come as a surprise – she has a PhD in organometallic synthesis, the study of compounds containing carbon atoms and metals. But after graduation Julia decided that she didn’t want to work in a lab – she was more interested in helping others learn about science. So after earning her degree, she became a project manager for science education programs at Oak Ridge Associated Universities in Tennessee, USA.

As a project manager, Julia’s job is to coordinate events for the Science Saturday program for primary and secondary school students. She organises the teams of scientists and teachers who create presentations and activities for the events. She also works with them to make sure that the science material covered is fun and easy to understand. Each event within the program focuses on a different topic, and Julia has worked on everything from x-rays to rainbows to robots.

Sometimes Julia organises educator programs for teachers, too. She loves seeing them get just as excited about science as their students, especially since some of her own teachers had helped her discover her love for science. Without their encouragement, Julia says, she wouldn’t have pursued science as a career. Growing up, Julia thought that, as a girl, she would be no good at maths or chemistry. But by Year 12 she was the only girl in her honours Physics class and was scoring top marks!

When she isn't getting crafty with her hands-on science lessons, Julia enjoys other hands-on activities like quilting, cross-stitch, and embroidery, as well as biking and cooking. Question 1

Interview: Arrange a short chat with one of your current or past science teachers and find out:

what they most enjoy about teaching science; whether teaching was their first career; what strategies they use to try and make their lessons fun and easy to understand; and what advice they would give to a year 10 student about finding the right career path to follow.

Cosmos Live Learning team

Lesson authors: Hayley Bridgwood and Kathryn Grainger Profile author: Megan Toomey Editors: Bill Condie, Jim Rountree and James Whitmore Art director: Robyn Adderly ​Education director: Daniel Pikler