We explain what a triple bond is, its characteristics and we give several examples
What is a triple covalent bond?
The triple covalent bonds are chemical bonds in which two atoms share three pairs of electrons. That is to say that they are covalent bonds formed by a total of six valence electrons that revolve around two atoms.
There are many chemical compounds that contain triple bonds. For example, organic compounds such as alkynes contain CC triple covalent bonds. Nitriles are also characterized by having a carbon-containing group linked to a nitrogen through a CN triple covalent bond. Other inorganic compounds, such as molecular nitrogen in air, also contain triple covalent bonds.
Having 6 electrons revolving around two nuclei gives triple bonds many unique characteristics. Both the shape of the molecules that contain them and the chemical reactions in which they can participate are different from those of double or single bonds.
Characteristics of the triple covalent bond
They are made up of 6 electrons.
These bonds are made up of 6 electrons and are formed when each of the two atoms involved shares three of their unpaired electrons with the other. This is the reason why they are called triple bonds, since they have three times the number of electrons of the single covalent bond.
They have one sigma (σ) bond and two pi (π) bonds.
Similar to double bonds, triple bonds are also formed by a sigma bond passing through the center of the line joining the two bonded atoms. However, unlike double bonds that have one, triple bonds have two pi bonds in addition to the sigma bond.
They almost always form linear compounds.
When two carbon atoms form a triple bond, each still has the possibility of forming an additional single bond with another atom (since carbon can form 4 bonds in total).
In these cases, both the two carbons and the other two atoms attached to them will form a straight line. This shape that the molecule acquires is called linear geometry.
They are the strongest covalent bonds
By comparing the triple bonds between two atoms with the double and single bonds between those same atoms, it is seen that triple bonds are always stronger than other types of covalent bonds. This means that it is more difficult to break a triple bond than a single or double bond.
This is because, in addition to having to break the sigma bond (which is also present in both single and double bonds), you have to break not one (as in double bonds) but two additional pi bonds.
They are shorter than double bonds or single bonds.
By the very fact of being stronger bonds, triple bonds manage to bring the nuclei of atoms closer to each other, which makes triple bonds shorter than double and single bonds.
They represent two unsaturations
Each carbon that has a triple bond will have only one additional bond with another atom. This means that said carbon would be bonded to only two atoms, instead of four, so it has fewer hydrogens than it could if it only formed single bonds.
This is called unsaturation, and compounds with triple bonds have two unsaturations, since each of the two carbons would fit 2 additional hydrogens, were it not for the triple bond.
They are rigid links
Like double bonds, triple bonds are stiff and hard to bend or twist. This is due to both the greater bond strength and the shorter length.
They can act as bases
Some compounds with triple bonds can use the pi electrons of said bond to bind or accept H+ ions, thus acting as bases.
They can be hydrogenated to give double or single bonds.
Triple bond unsaturations can be removed by breaking the pi bonds and adding hydrogens to the two carbons. This is called hydrogenation. If just one hydrogen molecule is added to a triple bond, it will become a double bond. If two hydrogen molecules are added, it will become a single bond.
Examples of triple covalent bonds
Nitrogen molecule (N2)
The nitrogen molecule contains a triple covalent bond between the two nitrogen atoms. Each atom shares its three unpaired valence electrons with the other, and each new pair of electrons goes on to form either the sigma bond or one of the two pi bonds that the molecule possesses.
In this case, both the two nitrogen atoms and the lone pairs of electrons each possesses are located along a straight line.
Propyne (an alkyne with the formula C3H4)
Propyne is the second simplest alkyne that exists. This compound is formed by a chain of three carbons, two of which are linked by means of a triple covalent bond.
Here you can also see that the three carbons and the last hydrogen atom (the one on the right) form a straight line. It can also be seen from the model that the single DC link is longer than the triple DC link.
Carbon monoxide (CO)
Carbon monoxide is a toxic inorganic gas that has a negative carbon atom and a positive oxygen linked by a triple covalent bond. In this case, it is a polar bond, due to the difference in electronegativities between carbon and oxygen.