1. Chemical Formulas & Formula Mass

2. Subscripts in Chemical Formulas
Subscripts show # atoms each element in formula
No subscript – understood to be 1
Subscripts refer to element immediately preceding them
Subscripts after parentheses refer to everything inside ( )

3. Coefficients Numbers in front of formulas
Refer to everything in formula
to count atoms: coefficient x subscript

4. Chemical Formulas H2O: 2 hydrogen, 1 oxygen
NH3: 1 nitrogen, 3 hydrogen
CH4 has ?
CO2 has ?
AgNO3 has ?
Al(NO3)3 has ?
1 carbon, 4 hydrogen
1 carbon, 2 oxygen
1 silver, 1 nitrogen, 3 oxygen
1 aluminum, 3 nitrogen, 9 oxygen

5. No. of atoms in formulas
Subscript outside ( ) x subscript inside ( ) = # of atoms
Al(NO3)3
Al = 1
N = 1 X 3 = 3
O = 3 X 3 = 9
Total = 13

6. No. of atoms in formulas Mg3(PO4)2 Mg = 3 P = 2 X 1 = 2 O = 4 X 2 = 8
Total = 13

7. Molar mass of an element
Molar mass = mass in grams of 1 mole of any pure substance
Molar mass of element = to atomic mass
units change from amu to grams per mole

8. Molar mass of elements Na:
atomic mass of 23 amu so molar mass = 23grams/mole K:
atomic mass of 39 amu so molar mass =
39 grams/mole
Ca:
atomic mass of 40 amu so molar mass =
40 grams/mole

9. Molar Mass of Compounds
= sum of masses of atoms in formula
Round atomic masses to whole number
Ex: H2O
2 X H = 2 X 1 = 2
1 X O = 1 X 16 = 16
Sum = = 18 g/mol

10. Molar Mass of Compounds
Try CH4
1 x C = 1 X 12 = 12
4 x H = 4 X 1 = 4
Sum = = 16 g/mol