The Periodic Table

A. History of the Periodic Table 1. First developed by Dmitri Mendeleev in Mendeleev was looking for a way to arrange the elements. 3. As he studied properties such as atomic mass, he noticed a repeating pattern.

Side Note: What does “ Periodic ” mean?? “Periodic” means “repeated in a pattern”! HOWEVER, Mendeleev had to leave some spaces because not all elements lined up according to atomic mass. Notice that he used his information to PREDICT masses. Very scientific……!

B. The Modern Periodic Table 1. c. 1914: Henry G.J. Moseley realized that elements could be arranged according to atomic NUMBER rather than mass.

2. Seaborg (1944) a. rearranged Periodic Table with...  Lanthanide and Actinide Series pulled out/separated from main Periodic Table b. discovered 10 new elements & countless isotopes

B. Arrangement of the PT 1. The boxes are arranged into vertical columns called groups or families. They are numbered a. The group numbers tell us the number of electrons in that element’s outer energy level - the number in red

b. valence electrons electrons found in the outermost energy level

c. Octet Rule We just said that the “ red number ” in the family/group number = the number of electrons in the outer shell or valency. Octet Rule: The tendency of atoms to gain or lose electrons so they acquire eight electrons in their outer energy level.

d. Groups to Know Group 1 - Alkali Metals Group 2 - Alkaline Earth Metals Group 17 - Halogens Group 18 - Noble Gases

2. Periods a. The boxes are arranged into horizontal rows called periods. b. The period numbers tell us the number of energy levels that an atom has c. Periods are numbered 1 through

3. Regions of the Periodic Table a. Metals - to the left of the stair-step line b. Non-Metals - to the right of the stair-step line c. Metalloids - on the stair- step line

a. Metals Found to LEFT of zigzag line on table Good conductors of heat & electricity Malleable Ductile High melting points Shiny Tend to lose electrons

b. Nonmetals Found to RIGHT of zigzag line on table Poor conductors of heat & electricity Brittle when solid Dull Low melting points Tend to gain electrons

c. Metalloids/Semi-Metals Found along both sides of zigzag line Properties of both metals & nonmetals Okay conductors of heat & electricity Shiny or dull

C. Trends in the Periodic Table Valence number Charge of ion (positive or negative) Tendency to gain or lose electrons Metallic vs. nonmetallic properties Atomic size (radius) Ionization energy Electronegativity (which ones WANT electrons the most)

1. Across a Period radius decreases (size of atom gets smaller) ionization energy increases electronegativity increases b/c  number of valence electrons increases…  so EMF increases…  so valence electrons held more tightly…

2. Down a Family radius increases ionization energy decreases electronegativity decreases b/c  number of energy levels increases…  so valence electrons held less tightly…