1. Chemical Formulas: Formula Mass & Molar Mass

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

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

4. Molar mass of elements Na has atomic mass of 22.98977 amu Na has atomic mass of 22.98977 amu molar mass = 22.98977 grams/mol molar mass = 22.98977 grams/mol K has atomic mass of 39.0983 amu K has atomic mass of 39.0983 amu molar mass = 39.0983 grams/mol molar mass = 39.0983 grams/mol Ca has atomic mass of 40.08 amu so Ca has atomic mass of 40.08 amu so molar mass = 40.08 grams/mol molar mass = 40.08 grams/mol

5. Round masses to whole number Na = 22.98977 grams rounds to 23g K = 39.0983 grams rounds to 39g Ca = 40.08 grams rounds to 40g rounds to 40g

6. Molar Mass MOLAR mass: always refers to mass in grams per mole (g/mol) MOLAR mass: always refers to mass in grams per mole (g/mol) formula mass (FM) or gram formula mass (GFM): refers to mass in grams (g) formula mass (FM) or gram formula mass (GFM): refers to mass in grams (g) for amounts other than one mole for amounts other than one mole

7. Mole to Mass conversions use PT for conversions involving mass 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 all atoms in compound's formula = to sum of masses of all atoms in compound's formula round atomic masses to whole number round atomic masses to whole number ex: H 2 O 2 H’s = 2 x 1g = 2g 2 H’s = 2 x 1g = 2g 1 O = 1 x 16g = 16g 1 O = 1 x 16g = 16g FM of H 2 O is sum: 2g + 16g = 18g FM of H 2 O is sum: 2g + 16g = 18g molar mass of H 2 O is 18g/mol molar mass of H 2 O is 18g/mol

9. Molar Mass of Compounds CH 4 1 C = 1 x 12g = 12g 1 C = 1 x 12g = 12g 4 H’s = 4 x 1g = 4g 4 H’s = 4 x 1g = 4g FM is sum = 4g + 12g = 16g FM is sum = 4g + 12g = 16g molar mass is 16g/mol molar mass is 16g/mol

10. challenge: find FM of CuSO 45H 2 O 4Ba 3 (PO 4 ) 2