Valence Electrons

the electrons in the outermost shell

Shell is another way to say energy levels

Atoms want to have a stable outer shell of electrons

Being completely full of electrons

or just having full s and p subshells/sublevels (they mean the same thing)

Noble Gases have 8 valence electrons - full s and p subshells

Atoms want to have a "Noble Gas" configuration

They will either gain electrons and become anions (negatively charged)

or they will give up electrons and become cations (positively charged)

Groups 1-3 (or 1A-3A) give up electrons - gets them to having 8 electrons in their outer shell

Groups 15-17 (or 5A-7A) gain electrons - their outer shell becomes empty, so the shell below it becomes the new outer shell, it is already full

Old group (groups are columns) number (1A-8A) = number of valence electrons

Lithium- 1 valence electron

Beryllium - 2 valence electrons

skip across to Boron - 3 valence electrons

Carbon - 4; Nitrogen - 5; Oxygen - 6; Fluorine - 7; Neon - 8

Find the highest shell number (the first number in a term)

(1s2 - shell number is 1; 3p4 - shell number is 3)

Add the number of electrons in that shell

ex. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3

highest shell number is 4, so add 4s2 (2 electrons) and 4p3 (3 electrons) = 5 valence electrons