1. March 21st
Chemical Compounds and
Formulas and Diagrams 21

2. Chemical Compounds and Formulas

3. Chemical Compounds are pure substances that contain two or more different elements in a fixed proportion. They are formed when elements combine together in chemical reactions.
For example: Water (H2O) – there are always twice as many hydrogen particles as there are of oxygen particles.

4. A chemical formula is the combination of symbols that represents a particular compound.
A chemical formula indicates which elements are found in the compound, as well as the number of atoms of each element that are found in the compound.

5. Examples:
NaCl – 1 atom of Na – sodium
- 1 atom of Cl – chlorine
H2O – 2 atoms of H – hydrogen
- 1 atom of O - oxygen

6. Rules For Writing The Formulas for Ionic Compounds

8. Examples: Sodium chloride Magnesium Oxide NaCl - Na (metal) – sodium
- Cl (non-metal) – chloride
Mg2O3 -Mg (metal) – magnesium
- O (non-metal) - oxide
Sodium chloride
Magnesium Oxide

9. Try These
Ca3P2 –
Li3N –
K2S –

10. Try These
Ca3P2 – Calcium phosphide
Li3N – Lithium nitride
K2S – Potassium sulfide

11. Write the chemical name for the following ionic compounds.
CoSe
HgF2
Na3P
Ba3As2
CaBr2

12. Ball and Hook Diagrams
The number of atoms varies from compound
to compound.
The number of atoms in a compound is
determined by the combining capacity of the
elements involved.
Hook Diagrams show the bonding capacity
and number of bonds. All bonds (hooks)
must be filled.

13. The result is the compound calcium chloride (CaCl2)
All hooks must be filled
to satisfy both substances.
Unsatisfied
The result is the compound calcium
chloride (CaCl2)