Valence electrons  These are the electrons on the outermost ring. They are available for bonding.  They can be found by counting the columns on the Periodic Table.  EX: P in group 5A = 5 valence electrons

Common Ion  In order to be stable, all elements want an electron configuration of a NOBLE GAS.  They will gain or lose electrons to complete their outside shell.  The periodic table will help you to be able to predict this.

Atomic Size

Atomic Radius – the distance from the center of an atom’s nucleus to its outermost electron

Atomic Radius Trends: 1. Atoms get larger as you move down a group  WHY? As you move down a group, the valence electrons are on higher principle energy levels which are further from the nucleus

2. Atoms get smaller as you move from left to right across a period  WHY? As you move from left to right across a period there are more protons pulling the electrons in more closely causing it to be smaller

 If your trends contradict each other, always use the PRINCIPLE ENERGY LEVEL TO DECIDE!!!

Getting larger

Which is the larger atom? S or O?  S because its valence electrons are on the 3 rd EL while O’s are on the 2 nd EL

Which is the larger atom? F or Se?  Se because its valence electrons are on the 4 th EL while F’s are on the 2 nd EL

Which is the larger atom? C or O?  C is because they are on the same EL so the one with fewer protons will be larger (less pull from the nucleus)

Which is the larger atom? N or S?  S because it is on the 3 rd EL while N is on the 2 nd EL