The Periodic Table Adapted from: Available

I. Introduction. –An element is identified by its chemical symbol. –The number above the symbol is the atomic number (# of protons) –The number below the symbol is the rounded atomic weight (mass number) (# of protons and neutrons) of the element. –.–. The periodic table is organized in rows and columns of related elements (next slide). This is because similar physical and chemical properties recur periodically when the elements are listed in order of increasing atomic number

1. I. Introduction A row is called a 1. period (same # of e- energy levels) A column is called a 2. family or group (same # of e- in outer energy level) 2.

II. Periods –The chemical behavior of elements is determined by its electron configuration –Electrons orbit the nucleus of an atom in distinct energy levels (“shells”). –Each period (row) on the periodic table represents a new energy level (“shell”) of electrons, so….. –Each period begins with a new outer electron energy level –Each period ends with a completely filled outer shell that has the maximum number of electrons for that energy level (usually 8).

III. Families/ Groups –The number identifying the families identifies the number of electrons in the outer energy level/”shell”, except helium –The outer “shell” electrons (valence electrons) are responsible for chemical reactions. –Elements in Families I-VIII are called representative elements –Group B elements (middle of periodic table) are called transition elements.

III. Families –IA are called alkali metals because the react with water to from an alkaline solution These need only one electron to empty their outer shell They are very reactive –Group IIA are called the alkali earth metals because they are reactive, but not as reactive as Group IA. They are also soft metals like Earth. –Group VIIA are the halogens These need only one electron to fill their outer shell They are very reactive. –Group VIIIA are the noble gases as they have completely filled outer shells They are almost non reactive.

III. Families Four important chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA). The elements on the left of the periodic table are metals. Elements on the right are non-metals. Semiconductors (metalloids) occur at the dividing line between metals and nonmetals

The location of metals, nonmetals, and semiconductors in the periodic table. Black line separation. Gases in white

V. Valence Electrons Chemical behavior is determined by the outer electrons. These are called valence electrons The noble gases have completely filled outer shells and are therefore stable. All other elements react so as to FILL or EMPTY their outer shell and become more stable. These outer shell electrons are represented using electron dot diagrams. see next slide Na Ne

Electron dot notation (showing valence electrons) for the representative elements (electrons present in outer shell). Need 1 to be full Give up 1 to be empty Need 2 to be full

V. Summary: The periodic table of the elements. Noble Gases Non-metals Halogens Alkali Earth Metals Alkali Metals Metals 2 e- (in 1st level when stable, full) 8 e- (in 2nd level when stable, full) 8 e- (in 3rd level when stable (18 when full)) 8 e- (in 4th level when stable (32 when full)) 8 e- (in 5th level when stable (50 when full)) 8 e- (in 6th level when stable (72 when full)) 7th level (varies) Periods Families/Groups 1e- 2e-3e-4e-5e-6e-7e- 8e- (except He) # of p # of p + n