yes cause its copper
A copper penny turns green due to oxidation. When oxygen combines with copper, it produces copper oxide, which is green, in color.
The penny has copper in it. Copper reacts to the oxygen in the air by producing copper oxide therefore turning green. The older the coin, the more copper in the coin.
The only wan to stop brass from turning your skin green is to coat it. The green is the copper from the brass alloy (brass is made from varying combinations of copper and zinc).
The word is "oxidation", which in the case of copper is a three-step process where the copper oxidizes to copper oxide, then to cuprous or cupric sulfide, and then to copper carbonate. Copper carbonate is the green colored copper or patina that forms over time. The old name for this green patina is "verdigris".
It is chemical. The copper in bronze turns green when it oxidizes.
Copper does react with air. It oxidizes turning a bluey-green colour, i.e the statue of liberty.
It is a chemical change.