Atoms interact or bond with one another so as to fill their outer shells with the maximum number of electrons. Hydrogen’s nucleus has only 1 proton, indicated by the +1. One electron orbits in a shell that would be filled with two. Two hydrogen atoms in close proximity can share their electrons, so that each has 2 some of the time. This sharing of electrons is a covalent bond. Here we see several molecules that are the result of covalent bonding.