A hypervalent molecule is a molecule that contains one or more typical elements (group 1, 2, 13-18) formally bearing more than eight electrons in their valence shells. PCl₅, SF₆, ICl₂⁻, PO₄³⁻, and I₃⁻ are examples of hypervalent molecules. Hypervalent molecules were first defined by Jeremy I. Musher in 1969 as molecules of the elements of group 15-18 in any oxidation state other than the lowest. In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... A periodic table group is a vertical column in the periodic table of the chemical elements. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... The valence shell is the outermost shell of an atom, which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms. ... Sulfur hexafluoride (SF6) is a gas whose molecules consist of one sulfur atom and six fluorine atoms. ... In inorganic chemistry, a phosphate is a salt of phosphoric acid. ... Triiodide is an iodine ion. ... 1969 (MCMLXIX) was a common year starting on Wednesday (the link is to a full 1969 calendar). ... In chemistry, the oxidation state is a measure of the degree of oxidation of an atom in a chemical compound. ...

Since the hypervalent molecules do not seem to obey the octet rule, some models have been proposed to describe their bonding properties. At first, hypervalent bonding was believed to be described as sp³d and sp³d² hybrid orbitals composed of s, p, and d-orbitals at higher energy levels. However, advances in the study of ab initio calculations have revealed that the contribution of d-orbitals to hypervalent bonding is too small to describe the bonding properties, and this hybrid orbital description is now regarded as much less important. The octet rule is a simple chemical theory that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, similar to the electronic configuration of a noble gas. ... four sp³ orbitals three sp² orbitals In chemistry, hybridisation or hybridization (see spelling differences) is the mixing of atomic orbitals belonging to a same electron shell to form new orbitals suitable for the qualitative description of atomic bonding properties. ... The current version of the article or section reads like an advertisement. ...

As another description of hypervalent molecules, modifications of the octet rule have been attempted to involve ionic characteristics in hypervalent bonding. As one of these modifications, in 1951, the concept of the 3-center-4-electron (3c-4e) bond, which described hypervalent bonding with a qualitative molecular orbital, was proposed. The 3c-4e bond is described as three molecular orbitals given by the combination of a p orbital on a central atom and two ligand orbitals: an occupied bonding orbital, an occupied non-bonding orbital (HOMO), and an unoccupied anti-bonding orbital (LUMO). 1951 (MCMLI) was a common year starting on Monday; see its calendar. ... 3-center-4-electron bond is a term for the axial bonds on a trigonal bypyramidal or octahedral molecule such as Phosphorous V Chloride. ... Electron atomic and molecular orbitals In quantum chemistry (electronic structure theory), the molecular electronic states, i. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... Look up homo in Wiktionary, the free dictionary. ... HOMO and LUMO are acronyms for Highest Occupied Molecular Orbitals and Lowest Unoccupied Molecular Orbitals respectively. ...

Several specific classes of hypervalent molecules exist:

• Hypervalent iodine compounds are useful reagents in organic chemistry.
• Sulfuranes and persulfuranes are hypervalent sulfur compounds.

Periodinanes are chemical compounds containing hypervalent iodine. ...

References

• Gillespie, R. J.; Silvi, B. The octet rule and hypervalence: two misunderstood concepts. Coord. Chem. Rev. 2002, 233-234, 53-62. [1]
• Musher, J.L. The Chemistry of Hypervalent Molecules Angew. Chem. Int. Ed. Engl. 1969, 8, 54-68. [2]