For our purposes, we need to be concerned only with those elements which are of primary importance in living systems. Each element is given a name, and symbolized by one or two letters, either the initials or an abbreviation of the English or Latin name for the element. In each element, all of the atoms have a particular number of protons. This number, the atomic number, can be used to identify the element. Since all complete atoms are electrically neutral, the atomic number also predicts the number of electrons present in the atom.
Atoms also have a predictable mass.
The mass of an atom is given by the sum of the protons and neutrons in the atomic nucleus. This value is given as the atomic weight or atomic mass of the element. You may also see the information given for a single element by the use of subscripted and superscripted values. Use this information to complete the following table, giving the characteristics of atoms of each of the six elements. The electrons of an atom lie outside the nucleus.