If we use our conventional system of units, where force is in newtons (N, = kg.m.s-2), charge is in coulombs (C) and distance is in metres (m), we need to incorporate a constant to this formula- conventionally and not at all intuitively, we write:
| F = | q1q2 |
| 4πε0r2 |
Where ε0 = 8.854 187 816 ×10-12 C2s2m-3kg-1.
This law, called Coulomb's Law, is valid for electrically charged planets, or really really teensy things like electrons and nuclei.
Types of Bonding
There are several different ways in which matter can be bound together, but on scales between the subatomic and the astronomical they all come back to Coulomb's law, the attraction between things of opposite charges, and the repulsion between things of the same charge. Nuclei will repel on another; electrons will repel one another; and nuclei and electrons will be mutually attractive. The interplay between these three things gives rise to the various forms of bonding we see both within molecules and between molecules.
Covalent
When electrons are strongly attracted to two different nuclei, they act as a sort of molecular glue, holding the nuclei together. Bringing two separated atoms together will give rise to an attraction, as the electrons on each atom are attracted to the nuclei on the other, and to a repulsion, as the electrons and nuclei are brought closer to each other. Often, the attractive force wins - lucky for us, or there would be little chemistry to study or living organisms to study it.
The net strength of the overall attraction is strongly dependent on where exactly the electrons are relative to the nuclei, so covalent bonding tends to give rise to very well defined regions of high electron density and bonds of fixed direction and length.
