1. The Nature of Chemical Bonds
Chapter 12

2. Homework Assignment Chap 12
Review Questions (p 262): 1 – 24
Multiple Choice Questions:

3. Electron Shells and Chemical Bonding
Valence electrons
Full capacity of a shell = 2n2
Group 1A
Group 7A

4. Show one dot for each valence electron in the atom
Fig 12.3
Show one dot for each valence electron in the atom

5. Fig 8.20 Electron dot notation for representative elements 1 83 4 5 6 7
Valence electrons – outermost electrons in an atom
Octet rule – atoms attempt to acquire 8 valence electrons

6. Closer look at the inert gases
Inert gas atoms have filled valence shells
Except for He, all have 8 valence electrons in
4 nonbonding pairs
Octet rule: An atom will gain. lose, or share
valence electrons until it is surrounded
by 8 valence electrons.

7. Example:

8. Three Types of Chemical Bonds
Ionic bonds
Electrons are transferred from one atom to another
Occur between a metal atom and a nonmetal atom
(2) Covalent bonds
Electrons are shared between two atoms
Occur between two nonmetal atoms
Metallic bonds
Metal atoms share many electrons in a “sea” that is free to move throughout the metal

9. The Ionic Bonds and Ionic CompoundsNa
Na+ + e-
e- + Cl - Cl - Na + Cl
Na+
NaCl
Opposite charges hold ions together
Form between metals and nonmetals

10. This energy is called the heat of formation
Formation of an ionic bond Na
11 protons
11 electrons
Na+
11 protons
10 electrons
+ e−
Cl-
17 protons
18 electrons Cl
17 protons
17 electrons
Net reaction: Na + Cl → Na+Cl− + energy
This energy is called the heat of formation

11. Fig. 12.7(a) Model of the sodium chloride crystal
No molecules in an ionic compound!
Formula unit + −
Na+ ions
Cl− ions

12. Fig. 12.7(b) The crystal structure of sodium chloride

13. Ionic compounds consist of a combination of
Ionic compounds consist of a combination of positive ions and negative ions
Ions are formed as nonmetal atoms gain and metal atoms lose electrons to achieve stable noble gas structure
The sum of the charges on the positive ions and negative ions in each formula unit must equal zero
How do we determine the formula for an ionic compound?