1 The Octet Rule Chapter 3 Section 3

2 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. Valence Electrons

3 Electrons are divided between core and valence electrons B 1s 2 2s 2 2p 1 Core = [He], valence = 2s 2 2p 1 Br [Ar] 4s 2 3d 10 4p 5 Core = [Ar] 3d 10, valence = 4s 2 4p 5

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 electron (11 e-) (10 e-) Mg  Mg electrons (12 e-) (10 e-) Al  Al electrons (13 e-) (10 e-) Na +, Mg 2+, Al 3+, and Ne are all isoelectronic.

7 Ion Formation - Anions N + 3 electrons  N -3 (7 e-) (10 e-) O + 2 electrons  O 2- (8 e-) (10 e-) F + 1 electron  F - (9 e-) (10 e-) N -3, O 2-, F -, and Ne are all isoelectronic.