1. Chemical Formulas: The Basics

2. Subscripts in Chemical Formulas
Numbers inside formulas & below line of type
Subscripts show number of atoms of each element

3. Rules for Subscripts in Formulas
No subscript – it’s understood to be 1
Subscripts refer to element immediately preceding number Remember – every element symbol starts with upper case letter
Subscripts after parentheses refer to everything inside ( )

4. Chemical Formulas H2O has: 2 hydrogens and 1 oxygen
NH3 has: 1 nitrogen and 3 hydrogens
CH4 has ?
CO2 has ?
AgNO3 has ?
1 carbon and 4 hydrogen
1 carbon and 2 oxygen
1 silver, 1 nitrogen, 3 oxygen

5. No. of atoms in formulas Hint: Look for uppercase letters!
Subscript outside ( ) multiplied by
subscript inside ( ) = # of atoms
Al(NO3)3
Al =
N =
O =
Total = 1
1 x 3 = 3
3 x 3 = 9
13 atoms
Hint: Look for uppercase letters!

6. Coefficients Numbers in front of formulas
Refers to everything immediately following in formula
No coefficient? understood to be 1

7. Coefficients 2H2O means 2(H2O) To count atoms -
multiply: coefficient x subscript
2 x 2 = 4 H’s
2 x 1 = 2 O’s

8. Hydrates
group salts that have water molecules stuffed in their empty spaces
Formulas are distinctive
Ex: CuSO45H2O
 means “is associated with” or “included”
doesn’t refer to multiplication
Not true chemical bond:
structure is definite
number empty spaces is definite
number water molecules is definite

9. CuSO45H2O Count up the atoms! 1 Cu 1 S 4 + 5x1 = 9 O 5x2 =10 H
total = 21 atoms

10. 5CuSO45H2O Count up the atoms! 5 = Cu 5 = S 5x4 + 5x5x1 = 45 O
5x5x2 = 50 H
total = 105 atoms