pennies nowadays are made from zinc with copper coating-- sheets are rolled thru a press that punches out planchets (the round coin). it then goes into the press that has an obverse and reverse die that imprints both sides. sometimes there are a few that get by without imprints-- these are called blanks-- there are also double struck coins- broadstruck coins -- off center coins- filled dies etc. these are oddities and valued by some collectors. since the cost of copper rose to high levels the mint started making them in zinc in 1980 and are copper coated after this date
Pennies are 97.5% zinc with a 2.5% copper coating. The acid ate away at the zinc leaving the copper shell.
Pennies are made from two different metals. The inside is a less valuable metal covered with a copper shell. My science teacher in high school filed the sides of a penny and put it in hydrochloric acid. The HCl ate the metal on the inside of the penny and left a thin copper shell on the outside.
