1. Chemical Bonding Review
Molecules
Salts & Formula Units
Chemical Bonding Review
Chemical Bonds: Forces that hold molecules and formula units together.

2. - + Ionic Bonding IONIC BOND Na 11 p+ 11 e- Cl 17 p+ 17 e-
Electron Transfer Between Neutral Atoms
1e-
Cl-
17 p+
18 e- -
Na+
11 p+
10 e- +
Electron Transfer Forms a sodium cation and a chlorine anion.
IONIC BOND
Opposite Charges ATTRACT!
…and this is the …..

3. Ionically Bonded Substances: Metal/Non-metal Combinations
What does the reaction of Na(s) metal and Cl2(g) look like? (movie)
2 Na(s) + Cl2(g)  2 NaCl(s) Energy (exothermic)
In Back
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Cl-
Na+
Crystal Lattice: 3 dimensional regular arrangement of points. Each point has identical surroundings.
In Front

4. Ionically Bonded Substances: Metal/Non-metal Combinations
Each Cl- or Na+ is shared with 6 neighbors.
There is no unique NaCl combination.
Therefore the written formula is the simplest RATIO of elements
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+
Cl-
1 Na : Cl
Na+
Cl-
Na+
Cl-
Cl-
Na+
And we write the FORMULA UNIT as
NaCl

5. Covalent Bonding Potential Energy Separation Distance H atom H atom
Atoms far apart?
Electrons Repel
High Potential energy
Still Closer?
Nuclei repel each other.
High Potential E.
Closer together? Nuclei are attracted to “SHARED ELECTRONS”
Attraction = COVALENT BOND
Low Potential Energy
H atom
H atom
H atom

6. H2 Crystal Lattice