What element of an amino acid makes it different from other types of amino acids?

The R group.

Explanation:

The basic structure of all amino acids are a central carbon atom attached to a hydrogen atom with a single bond. This carbon atom is also connected to an amino/amine group, NH2, and a Carboxyl Group, COOH. What differentiates amino acids from each other is the R group that is attached to the carbon atom as well, as it is unique to each amino acid. Thus, the R group is the element of an amino acid that makes it different from other types of amino acids. Hope this helped!