Answer:
The first energy level is closest to the nucleus. The second energy level is a little farther away than the first. ... The electrons in the energy level farthest from the nucleus are called valence electrons. Atoms in the same column (group) in the periodic table have the same number of valence electrons.
Explanation:
Amino acids carry two functional groups: an amine group (-NH2) and a carboxylic acid group (-COOH). They are different because they have different side chains (R groups) attached to an alpha carbon that is specific to each amino acid.
