In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, the double bond rule states that
elements with a
principal quantum number (''n'') greater than 2 for their
valence electrons (
period 3 elements and higher) tend not to form multiple bonds (e.g.
double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
s and
triple bond
A triple bond in chemistry is a chemical bond between two atoms involving six Electron pair bond, bonding electrons instead of the usual two in a covalent bond, covalent single bond. Triple bonds are stronger than the equivalent covalent bond, sin ...
s). Double bonds for these heavier elements, when they exist, are often weak due to poor
orbital overlap between the ''n''>2 orbitals of the two atoms. Although such compounds are not intrinsically unstable, they instead tend to dimerize or even
polymerize
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many form ...
. Moreover, the multiple bonds of the elements with ''n''=2 are much stronger than usual, because lone pair repulsion weakens their sigma bonding but not their pi bonding. An example is the rapid polymerization that occurs upon condensation of
disulfur, the heavy analogue of . Numerous exceptions to the rule exist. Several exceptions of this rule has been already made.
Triple bonds
References
{{Reflist
Chemical bonding