Groups 1 and 17 of the P.T.

Valence electrons: electrons in the outermost shell

Octet Rule: Most elements gain or lose electrons until they have 8 valence e^-

Ions: particles that have a net electric charge because  $electrons\ne protons$  

electron configuration: describes organization of electrons into energy levels (last digit is the valence shell)

Examples:   Na  2-8-1  ;  Cl  2-8-7

Potassium has 1 valence electron based on its configuration of 2-8-8-1

Each column of the Periodic Table is a unique Group of elements. (# 1 - 18)

Atoms of elements in Group 1 all have 1 valence electron.

This leads to similar chemical properties

Reactivity increases as you go down the Group

Name means "salt makers"

F, Cl, Br, I, At

Commonly, they have 7 valence electrons. (1 from the octet)

Reactivity decreases as you go down the Group.

Steal 1 e- to achieve octet status

"Salt" is a generic term for an ionic compound involving a halogen

NaCl

KBr

LiF

NaI