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Antibonding
 
 
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Antibonding (or anti-bonding) is a type of chemical bonding
Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
. An antibonding orbital is a form of molecular orbital
Molecular orbital

In chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region....
 (MO) that is located outside the region of two distinct nuclei
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
. The overlap of the constituent atomic orbitals is said to be 'out of phase' and as such the electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s present in each antibonding orbital are repulsive and act to destabilize
Reactivity

Reactivity refers to the Reaction rate at which a chemical substance tends to undergo a chemical reaction in time. In pure chemical compounds, reactivity is regulated by the physical properties of the sample....
 the molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 as a whole. (See Electron Phases
Electron Phases

In physical chemistry, Electron Phases describe the sign of the wave function, which is a solution to the Schr?dinger equation. When two wave functions describing two atomic orbitals on the same atom are combined, a hybrid orbital is created....
)

Antibonding molecular orbits (MOs) are normally higher in energy than bonding MOs.






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Encyclopedia


Antibonding (or anti-bonding) is a type of chemical bonding
Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
. An antibonding orbital is a form of molecular orbital
Molecular orbital

In chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region....
 (MO) that is located outside the region of two distinct nuclei
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
. The overlap of the constituent atomic orbitals is said to be 'out of phase' and as such the electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s present in each antibonding orbital are repulsive and act to destabilize
Reactivity

Reactivity refers to the Reaction rate at which a chemical substance tends to undergo a chemical reaction in time. In pure chemical compounds, reactivity is regulated by the physical properties of the sample....
 the molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 as a whole. (See Electron Phases
Electron Phases

In physical chemistry, Electron Phases describe the sign of the wave function, which is a solution to the Schr?dinger equation. When two wave functions describing two atomic orbitals on the same atom are combined, a hybrid orbital is created....
)

Antibonding molecular orbits (MOs) are normally higher in energy than bonding MOs. They are occupied by two electrons at a time and (in the case of hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
), each atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
 can contribute only one electron, therefore only the s (bonding) MO is occupied and the H2 molecule is more stable than two separate H atoms.

A molecular orbital becomes antibonding as there is actually less electron density
Electron density

Electron density is the measure of the probability of an electron being present at a specific location.In molecules, regions of electron density are usually found around the atom, and its bonds....
 between the two nuclei than there would be if there was no bonding interaction at all. When an MO changes sign (from positive to negative) between two atoms, it is said to be antibonding with respect to those atoms. Antibonding orbitals are often labelled with an asterisk
Asterisk

An 'asterisk' is a typographical symbol or glyph. It is so called because it resembles a conventional image of a star. Computer scientists and mathematicians often pronounce it as star ....
 (*) on molecular orbital diagrams.

In molecules with several atoms, such as benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
, a particular MO may be bonding with respect to some adjacent pairs of atoms and antibonding with respect to other pairs. If the bonding interactions outnumber the antibonding interactions, the MO is said to be "bonding," while if the antibonding interactions outnumber the bonding interactions, the MO is said to be "antibonding". Since each carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 atom contributes only one electron to the p-system
Pi bond

In chemistry, pi bonds are covalent bond chemical bonds where two lobes of one involved electron atomic orbital overlap two lobes of the other involved electron orbital....
 of benzene, there are six p-electrons and therefore only the three lowest-energy MOs (the bonding ones) are filled.

Another particular feature of antibonding is that the antibonding orbital is more antibonding than the bonding orbital is bonding. This leads to the conclusion that the energy of both MOs are raised by the presence of nucleus-nucleus repulsion.

Antibonding orbitals are also important for explaining chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
s in terms of molecular orbital theory. Roald Hoffmann and Kenichi Fukui
Kenichi Fukui

Kenichi Fukui was a Japanese chemist.Kenichi Fukui was co-recipient of the Nobel Prize in Chemistry in 1981 with Roald Hoffman, for their independent investigations into the mechanisms of chemical reactions....
 shared the 1981 Nobel Prize in Chemistry for their work and further development of qualitative
Qualitative

The term qualitative is used to describe certain types of information. Qualitative data are described in terms of quality . This is the converse of quantitative, which more precisely describes data in terms of quantity and often using a numerical figure to represent something in a statement....
 MO explanations for chemical reactions.