2. 3.1 Bonding

3. Ionic Bonding • • • • • Cl Na • • • • • [ Na ]+ [ Cl ]- • • • • • •
Form between a metal and a nonmetal
Simplest expressed form is called formula unit
Valence electrons are “stolen”
Typical ionic bonds are alkali halides such as sodium chloride (NaCl) • • • • • Cl
Metals lose electrons to get a stable outer shell
Nonmetals gain electrons to get a stable outer shell Na • • • • •
[ Na ]+
[ Cl ]- • • • • • •
Positive ions are
called cations
Negative ions are
called anions

4. Ionic Properties Very high melting points. Brittle crystals.
Many dissolve in water.
Good conductors of electricity if melted or dissolved.
Acids
Ionic compounds that have H+ and an anion
Molecular formula always starts with H
Name is derived from its anion and always ends with the word, acid.

5. Covalent Bonding Electrons are shared by both nuclei
Molecules are the smallest units of covalent compounds
Diatomic- element that always occurs in pairs
Br2, I2, N2, Cl2, H2, O2, F2
Know these
H2O Water
NH3 Ammonia
CH4 Methane

6. Covalent Properties Low melting points.
Many are liquids and gases at room temperature.
Polar covalent molecules dissolve in water.
Nonconductors of electricity.

7. Lewis Dot Diagrams NH3 H • • H N • • • • H • • H H N H • •
Dot Diagram Steps
1. Draw out atoms with valence electrons
2. Connect 2 e- to share until all atoms have full shells
3. Redraw H • • H N • • • • H • •
Sometimes more than one pair of electrons are shared:
Double Bonds= 2 pairs of electrons
Triple Bonds= 3 pairs of electrons H
Final Answer H N H • •

8. Drawing Hints Put the single atom in the middle of the dot diagram
Hydrogen is never in the middle of the dot diagram
When redrawing, we use dashes to represent 2 shared electrons
Remember to redraw the nonbonding electrons

9. Sample Problems
Draw
CH4
PCl3
SH2
HCl
CO2
BH3

10. CH4

11. PCl3

12. SH2

13. HCl

14. CO2

15. BH3 *note: B violates the octet rule (w/ 6e-)
*other exceptions, Be needs 4 valence e-, nonmetals in period 3 or higher MAY have 10 or 12 valence e-