From the mints website--
1920 to 1941
Composition: 95.5% copper, 3% tin, 1.5% zinc
Weight (g): 3.24
Diameter (mm): 19.05
Thickness (mm): 1.65
1942 to 1977
Composition: 98% copper, 0.5% tin, 1.5% zinc
Weight (g): 3.24
Diameter (mm): 19.05
Thickness (mm): 1.65
1978 to 1979
Composition: 98% copper, 1.75% tin, 0.25% zinc
Weight (g): 3.24
Diameter (mm): 19.05
Thickness (mm): 1.52
1980 to 1981
Composition: 98% copper, 1.75% tin, 0.25% zinc
Weight (g): 2.8
Diameter (mm): 19
Thickness (mm): 1.45
1982 to 1996
Composition: 98% copper, 1.75% tin, 0.25% zinc
Weight (g): 2.5
Diameter (mm): 19.1
Thickness (mm): 1.45
1997 to 1999
Composition: 98.4% zinc, 1.6% copper plating
Weight (g): 2.25
Diameter (mm): 19.05
Thickness (mm): 1.45
2000 to date
Composition: 94% steel, 1.5% nickel, 4.5% copper plating or copper plated zinc
Weight (g): 2.35
Diameter (mm): 19.05
Thickness (mm): 1.45
see
http://www.mint.ca/store/mint/learn/1-cent-5300004#1_1Joe