The chemical symbols of Calcium, Carbon, and Copper are: 

An element's chemical symbol typically consists of two characters. Every chemical symbol has a capital letter for the first letter and a tiny letter for the second

Calcium has an atomic number of 20 and is represented by the letter Ca. Carbon has an atomic number of 6 and is represented by the letter C. Copper has an atomic number of 29 and is represented by the symbol Cu.