Electric Potential


Metal Potential, Volts Metal Potential, Volts
Calcium +2.20 Hydrogen 0.000
Magnesium +1.87 Antimony -0.190
Aluminum +1.30 Arsenic -0.320
Manganese +1.07 Bismuth -0.330
Zinc +0.758 Copper -0.345
Chromium +0.600 Mercury -0.799
Iron +0.441 Silver -0.800
Cadmium +0.398 Platinum -0.863
Nickel +0.220 Gold -1.100

Some metals give up electrons more easily then others.  This difference is exploited in a battery to create a flow of electrons.
The above table can be used to calculate theoretical voltages for various metal combinations.

Link to more information about the electric potential of different metals.