1. Counting Atoms

2. How to Count Atoms
The symbol of an element represents one atom of that element.
e.g. Na = 1 atom

3. A subscript is a number written at the lower right corner behind the symbol of an element. If there is more than one atom of the element, then a subscript is used to indicate the number of atoms.
e.g. H2 = 2 atoms

4. A subscript outside a bracket multiplies all the elements inside the brackets.
e.g. Mg3(PO4)2 :
Mg = 3 atoms
P = 2 atoms
O = 8 atoms
Total Atoms: 13

5. (a) A coefficient is a number written in front of a chemical symbol and indicates the number of atoms of that element.
e.g. 3 C = 3 atoms OR

6. (b) A coefficient is a number written in front of a chemical formula and indicates the number of that compound.
NOTE: A coefficient multiplies the number of atoms of each element in the formula.

7. Examples
2 H2O
4 Hydrogen atoms
2 Oxygen atoms
Total Atoms: 6

8. 3 CuSO4
3 copper
3 Sulphur
12 Oxygen atoms
Total Atoms: 18

9. 4 Pb(NO3)2
4 lead
8 Nitrogen
24 Oxygen atoms
Total: 36

10. Homework Complete two worksheets on counting atoms Remember:
Element Project is due Nov 2
3D box needs to be handed in after you give your 3 min presentation