Copper until 1982. (Except 1943, steel.) The copper weighs 3.1 grams. In 1982 at the end of the year they switched from copper, to zinc. The zinc weighs 2.5 grams. So, if the date of your cent is 1983 or after, it's not copper.
Yes if it has had an extended soaking in acid, or if it was struck on a planchet that split before strike or if it was struck on a planchet punched from strip that was rolled very thin. In the first case the coin will still show all details, will have thin or none existant rims, and will be slightly smaller in diameter. In the second case it will be lacking in detail and on the split side you will see the rough surfaces of the split planchet in the detail areas. In the third case the details will be weak or missing, but the surfaces smooth in the weak detail areas. If none of the above and it is dated 1982 or later then it is almost certainly copper plated zinc.