Why are there so many different kinds of forces in chemistry?
Category: Chemistry Published: June 11, 2013
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Assistant Professor of Physics at West Texas A&M University
There is only one significant force at work in chemical reactions: the electromagnetic force. There are four fundamental forces in the universe: gravity, the electromagnetic force, the weak nuclear force and the strong nuclear force. Gravity is too weak to affect chemical reactions much, seeing as chemical reactions involve the rearranging of tiny atoms. Also, the nuclear forces don't play a role in chemical reactions. If a nuclear force becomes involved, then you are dealing with a nuclear reaction and not a chemical reaction. Every facet of chemistry is the result of one force: the electromagnetic force. However, because of the quantum wave nature of particles, this force can take on many forms. In a strict sense, every manifestation of the electromagnetic force is unique, as it depends crucially on the arrangement of atoms, the state of their electrons, their temperature, etc. To foster better understanding, however, chemists place the different forms of the electromagnetic force into broad classes:
- Covalent bonds: the binding electromagnetic force that arises between atoms when they closely share electrons in an approximately equal way.
- Metallic bonds: the binding electromagnetic force that arises between atoms and the delocalized conduction electrons of the metal.
- Ionic bonds: the binding electromagnetic force that arises between atoms that are ionized oppositely (one atom has a net negative charge and the other has a net positive charge).
- Ion-dipole bonds: the binding electromagnetic force that arises between molecules due to a permanent or induced electric dipole being attracted to an atom with a net electric charge.
- Dipole-dipole bonds: the binding electromagnetic force that arises between molecules due to their permanent electric dipoles.
- Hydrogen bonds: a special case of the dipole-dipole bond when hydrogen is involved, making the bond unusually strong.
- Rotating dipole-dipole bonds (Keesom bond, a type of Van der Waals bond): a weak, special case of the dipole-dipole bond when the molecules are rotating and not locked in place.
- Dipole-induced dipole bonds (Debye bond, a type of Van der Waals bond): the binding electromagnetic force that arises between a molecule with a permanent electric dipole and a molecule with no permanent electric dipole, but with an induced one.
- Induced dipole-induced dipole bonds (London dispersion bond, a type of Van der Waals bonds): the binding electromagnetic force that arises between two molecules without permanent electric dipoles due to the brief mutual induction of dipoles.