Chapter 5 Honors Notes the Periodic Table

Chapter 5 Honors Notes – The Periodic Table

Section 5.1 – Organizing the Elements

Dmitri Mendeleev was one of the first scientists to design a way of organizing elements. He studied the properties of the elements and looked for patterns among the properties. He found that if the elements were listed by increasing atomic mass, certain properties appeared at certain intervals within the list.

- Mendeleev was able to predict new elements and their properties while constructing the periodic table. - Mendeleev was not the only person to develop the periodic table, but he was the first to use the table to make predictions. - Throughout the construction of the periodic table, Mendeleev had to change the arrangement of the elements.

The modern periodic table organizes elements by atomic number. When the elements are arranged in this way, elements that have similar properties appear at regular intervals. This principle is known as the periodic law.

What about Mercury in fish on page 147?

Each row of the periodic table is a period. The periodic table has 7 periods.

- As you move from left to right across a period, properties such as reactivity and conductivity change, and elements become less metallic.

Each column of the periodic table is a group. For all groups, the elements in that group have similar chemical properties.

Section 5.2 – Exploring the Periodic Table

The Role of Electrons

The periodic table is organized by atomic number, which is the number of protons in an atom.

- The periodic trends in the periodic table are the result of electron arrangement. Specifically, the chemical properties of each group are largely determined by the number of valence electrons. - For example, find lithium and sodium on the periodic table. They each have one valence electron and therefore have similar chemical properties. - The elements in a group are not always exactly alike due to the different numbers of protons and electrons. Ion Formation

Atoms whose outer energy levels are not filled may undergo a process called ionization. That is, such atoms may gain or lose valence electrons so that they have a filled outermost shell.

- If an atom gains or loses electrons, it no longer has an equal number of electrons and protons. Because the charges do not cancel completely, the atom has a net electric charge. A charged atom is called an ion.

All elements in group 1 form positive ions.

- Lithium has 3 electrons. 2 of those electrons are in the first energy level and 1 is in the second energy level. The single valence electron is easily removed, which makes lithium very reactive. - Removing this electron forms a positive ion, or cation. A lithium ion is written as Li+.

All elements in group 17 form negative ions.

- Fluorine has 9 electrons. 2 of those electrons fill the first energy level and 7 fill the second energy level. A fluorine atom only needs one more electron to have a filled outermost shell. - Gaining this electron forms a negative ion, or anion. A fluorine ion is written as F-

How Are the Elements Classified?

All elements are either metals, nonmetals, or semiconductors.

Metals are shiny solids that can be stretched and shaped. They are good conductors of heat and electricity.

Nonmetals, except for hydrogen, are found on the right side of the periodic table. Nonmetals may be solids, liquids, or gases at room temperature. Solid nonmetals are often dull and brittle. They are poor conductors of heat and electricity.

Semiconductors are also called metalloids. Semiconductors share properties with metals and nonmetals. Semiconductors can conduct electricity under certain conditions and they are the main components of chips in computers and in other electronic devices. Section 5.3 – Families of Elements

The elements in a family have the same number of valence electrons.

Metals

Families of metals include the alkali metals, the alkaline-earth metals, and the transition metals.

Alkali Metals are soft and shiny and reacts violently with water. They are often stored in oil in order to prevent them from reacting with the moisture in the air.

- Alkali metals are very reactive because they only have one valence electron and it is easy to remove. When the valence electron is removed the element becomes positively charged. - Because they are so reactive, these elements are not found uncombined in nature. For example, sodium and chlorine form a compound to make sodium chloride.

Alkaline-earth metals are harder, denser, stronger, and have higher melting points than alkali metals.

- Alkaline-earth metals have 2 valence electrons and are less reactive. However, they still do react since they only have 2 valence electrons. - Alkaline-earth metals are found in hard shells of sea animals, coral, and skeletons of sea animals. - Magnesium is a useful alkaline-earth metal that acts as an enzyme that speeds up processes in the human body.

Transition metals are harder, more dense, and have higher melting points than alkali or alkaline-earth metals. They are also much less reactive.

-Transition metals can be used for jewelry, plumbing or electrical wiring, light bulb filaments, and they play an important part in the roles of the chemistry in your body.

Noble gases have a filled outermost shell. Therefore, they do not react with anything. They do not gain or lose electrons.

Halogens are the most reactive nonmetals. Halogens have seven valence electrons. With the addition of just one more electron, they become stable. For that reason, halogens combine easily with alkali metals.

Semiconductors are elements that are able to conduct heat and electricity under certain conditions.