A triple bond in chemistry is a

chemical bond A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing o ...

between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order of three. The most common triple bond, that between two

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

atoms, can be found in alkynes. Other functional groups containing a triple bond are cyanides and isocyanides. Some diatomic molecules, such as dinitrogen and

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

, are also triple bonded. In skeletal formulae the triple bond is drawn as three parallel lines (≡) between the two connected atoms.

Bonding

The types of bonding can be explained in terms of orbital hybridization. In the case of acetylene each carbon atom has two sp-orbitals and two p-orbitals. The two sp-orbitals are linear with 180° angles and occupy the x-axis ( cartesian coordinate system). The p-orbitals are perpendicular on the y-axis and the z-axis. When the carbon atoms approach each other, the sp orbitals overlap to form an sp-sp

sigma bond In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools o ...

. At the same time the p_z-orbitals approach and together they form a p_z-p_z pi-bond. Likewise, the other pair of p_y-orbitals form a p_y-p_y pi-bond. The result is formation of one sigma bond and two pi bonds. In the bent bond model, the triple bond can also formed by the overlapping of three sp³ lobes without the need to invoke a pi-bond.

Triple bonds between elements heavier than carbon

Triple bonds are found for many elements beyond carbon. They are common for transition metals. Hexa(tert-butoxy)ditungsten(III) and Hexa(tert-butoxy)dimolybdenum(III) are well known examples. The M-M distance is about 233 pm. The W2 compound has attracted particular attention for its reactions with alkynes, leading to metal-carbon triple bonded compounds of the formula RC≡W(OBut)₃.

References

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