The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction.
The strength of chemical bonds varies considerably;
- there are "strong bonds" such as covalent or ionic bonds and
- "weak bonds" such as dipole–dipole interactions,
- the London dispersion force and
- hydrogen bonding.
Since opposite charges attract via a simple electromagnetic force, the negatively charged electrons that are orbiting the nucleus and the positively charged protons in the nucleus attract each other.
An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position.
This attraction constitutes the chemical bond. Due to the matter wave nature of electrons and their smaller mass, they must occupy a much larger amount of volume compared with the nuclei, and this volume occupied by the electrons keeps the atomic nuclei relatively far apart, as compared with the size of the nuclei themselves. This phenomenon limits the distance between nuclei and atoms in a bond.
In general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms.
The atoms in molecules, crystals, metals and diatomic gases— indeed most of the physical environment around us— are held together by chemical bonds, which dictate the structure and the bulk properties of matter.