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Diatomic molecules (from Greek di- 'two') are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen ( H 2 ) or oxygen ( O 2 ), then it is said to be homonuclear .
Diatomic molecules consist of a bond between only two atoms. They can be broken into two categories: homonuclear and heteronuclear. A homonuclear diatomic molecule is one composed of two atoms of the same element. Examples are H 2, O 2, and N 2. A heteronuclear diatomic molecule is composed of two atoms of two different elements.
Although such compounds are not intrinsically unstable, they instead tend to dimerize or even polymerize. [1] 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. [ 2 ]
Atomicity may vary in different allotropes of the same element. The exact atomicity of metals, as well as some other elements such as carbon, cannot be determined because they consist of a large and indefinite number of atoms bonded together. They are typically designated as having an atomicity of 2.
For instance, in the simple case of a hydrogen diatomic molecule, promotion of a single electron from a bonding orbital to an antibonding orbital can occur under UV radiation. This promotion weakens the bond between the two hydrogen atoms and can lead to photodissociation, the breaking of a chemical bond due to the absorption of light.
For example, in the case of the F 2 molecule, the F−F bond is formed by the overlap of p z orbitals of the two F atoms, each containing an unpaired electron. Since the nature of the overlapping orbitals are different in H 2 and F 2 molecules, the bond strength and bond lengths differ between H 2 and F 2 molecules.
Several non-metallic elements exist only as molecules in the environment either in compounds or as homonuclear molecules, not as free atoms: for example, hydrogen. While some people say a metallic crystal can be considered a single giant molecule held together by metallic bonding , [ 20 ] others point out that metals behave very differently ...
Molecular orbital diagrams best illustrate isoelectronicity in diatomic molecules, showing how atomic orbital mixing in isoelectronic species results in identical orbital combination, and thus also bonding. More complex molecules can be polyatomic also. For example, the amino acids serine, cysteine, and selenocysteine are all isoelectronic to ...