Bonds: Hydrogen

The simplest atom is hydrogen consisting of a nucleus with a single proton and a single electron. The most common atom, that is element  in the known universe is hydrogen. Stars, such as the Sun are formed when huge clouds of hydrogen gas in space collapse under the influence of gravity. When the center of such a collapsing cloud becomes dense enough and hot enough nuclear fusion, the same process which powers the hydrogen bomb, occurs forming a star.

Unlike helium discussed in an earlier post hydrogen does not like to live in isolation. The single electron in a hydrogen atom occupies an unfilled electron shell. If importance is that hydrogen is the only atom to which quantum mechanics equations can be applied and solved exactly. This is fortunate because the functions that result from those equations, hydrogenic orbitals are used to calculate approximate solutions to quantum mechanics equations applied to more complex atoms and molecules.

Hydrogen's unfilled shell wants a second electron. However if a second electron is just added the atom has an overall negative(-1) charge which is not especially stable. Ideally and atom wants to fill its electron shells without giving the stuff made up of that matter an overall positive or negative charge. A way for hydrogen to accomplish this is to partner with another hydrogen and share a pair of electrons.

When this happens the two electrons spend more time on average between the nuclei. Because there is more negative charge on average between the nuclei than elsewhere the positive charged nuclei are pulled together by this "cloud" of negative charge. This is how bonds are formed.  Two atoms that form a bond form a molecule.