1. Chemical Formulas: Formula Mass & Molar Mass

2. Subscripts in Chemical Formulas
Subscripts show # atoms each element in representative unit
Subscripts after parentheses refer to everything inside ( )

3. Molar mass of an element
Molar mass = mass (in grams) of 1 mole of any pure substance
Molar mass of element is:
numerically equal to atomic mass, but
units change from amu to grams per mole (g/mol)

4. Molar mass of elements Na has atomic mass of 22.98977 amu
molar mass = grams/mol
K has atomic mass of amu
molar mass = grams/mol
Ca has atomic mass of amu so
molar mass = grams/mol

5. Round masses to whole number
Na = grams
round to 23 grams
K = grams
round to 39 grams
Ca = grams
round to 40 grams

6. Molar mass
Also called
formula mass or
gram formula mass

7. Mole to mass conversions
Use PT for conversions involving mass
Unless you want to memorize the masses of all the elements!!

8. Molar Mass of Compounds
= to sum of masses of atoms in compound's formula
Round atomic masses to whole number
Ex: H2O
2 H’s = 2 x 1g = 2g
1 O = 1 x 16g = 16g
Molar mass H2O is sum: 2g + 16g = 18g

9. Molar Mass of Compounds
Try CH4
1 C = 1 x 12g = 12g
4 H’s = 4 x 1g = 4g
Sum = 4g + 12g = 16g