The Octet Rule

1
The Octet Rule

• Chapter 3 Section 3

2
Valence Electrons

• Valence electrons - electrons in the outermost
  energy level
• Valence electrons are the most important because
  they are involved in chemical reactions.
• Electron configurations can help to determine the
  number of electrons in the outermost energy
  level.

3
Valence Electrons

• Electrons are divided between core and valence
  electrons
• B 1s2 2s2 2p1
• Core He , valence 2s2 2p1

Br Ar 4s2 3d10 4p5 Core Ar 3d10 ,
valence 4s2 4p5
4
Octet Rule
Atoms like to either empty or fill their
outermost level so they can become like the
closest noble gas. Since the outer level
contains two s electrons and six p electrons (d
f are always in lower levels), the optimum number
of electrons is eight. This is called the octet
rule.
5
Keep an Eye On Those Ions!

• Metal atoms form cations.
• Cation positively charged ion
• Nonmetal atoms form anions.
• Anion negatively charged ion
• Easy way to remember Cats are positive. Ants
  are negative.

6
Ion Formation - Cations

• Na ? Na 1 electron
• (11 e-) (10 e-)
• Mg ? Mg2 2 electrons
• (12 e-) (10 e-)
• Al ? Al3 3 electrons
• (13 e-) (10 e-)
• Na , Mg2 , Al3 , and Ne are all isoelectronic.

7
Ion Formation - Anions

• N 3 electrons ? N-3
• (7 e-) (10 e-)
• O 2 electrons ? O2-
• (8 e-) (10 e-)
• F 1 electron ? F-
• (9 e-) (10 e-)
• N-3, O2- , F-, and Ne are all isoelectronic.