While searching on the web, I found a great set of easy to understand notes on kinetics by Dr. Jeffery Mack from the California State University Sacramento (CSUS).
Link: Kinetic Notes
Below is a sample of these notes.
mass number

exact weight

percent abundance

12

12.000000

98.90

13

13.003355

1.10

mass number

exact weight

percent abundance

14

14.003074

99.63

15

15.000108

0.37
