A nonpolar covalent bond , also called a pure or apolar covalent bond, is the union of two atoms that share one or more pairs of electrons equally. This means that the electrons that form the bond spend approximately the same amount of time near one of the atoms as the other.
This type of bond occurs between two equal atoms (of the same element) or between two different atoms, but that have very similar electronegativities.
There are three types of chemical bonds that hold atoms together. These are: the ionic bond , the covalent bond, and the metallic bond. These bonds differ according to how the electrons are distributed around the atoms.
In the case of covalent bonds, the two atoms share the valence electrons, which means that these electrons, instead of revolving around one atom, revolve around both. However, this is not always fair, since electrons prefer to spend more time near the most electronegative atom, giving rise to a polar covalent bond.
Characteristics of the nonpolar covalent bond
1. They are formed between atoms with the same or very similar electronegativities
They are covalent bonds that are formed between the same atoms or that have very similar electronegativities. In general, a covalent bond is considered nonpolar if the difference in electronegativities is less than or equal to 0.4.
2. They can be single, double or triple
Depending on the number of pairs of electrons that both atoms share, nonpolar or nonpolar covalent bonds can be single, double or triple.
When the bond is made up of a single pair of electrons, it is called a single bond, when two pairs of electrons are shared it is called a double bond, and if three pairs of electrons are shared it is called a triple bond.
3. They almost always involve non-metals
Metals are elements with very low electronegativities that form metallic bonds with each other. When they bond with nonmetals, they always form either ionic bonds or polar bonds. For this reason, nonpolar covalent bonds only form between non-metallic elements such as hydrogen and carbon.
A compound that only has nonpolar covalent bonds will be made up of nonpolar molecules. These types of compounds are characterized by having low boiling and melting points compared to metals and ionic compounds (some are even gases at room temperature), they are insoluble in water and are poor conductors of heat and electricity.
5. They can form solid, liquid or gaseous compounds at room temperature.
Because nonpolar covalently bonded compounds can have low but highly varied boiling and melting points, some of them are gases at room temperature (such as hydrogen, H 2 , and nitrogen, N 2 , for example), others They are liquid (such as bromine, Br 2 ), while others are solid (such as naphthalene, C 10 H 8 ).
6. They have relatively low binding energies.
Compared to ionic bonds, nonpolar covalent bonds are easier to break as they have lower bond energy. This means that less energy must be used to break a nonpolar covalent bond than an ionic bond.
Examples of nonpolar covalent bonds
HH bond in the hydrogen molecule (H 2 )
In the hydrogen molecule, H 2 , two hydrogen atoms share their single valence electrons to form a single covalent bond.
Since both atoms are equal, the difference in electronegativities between the two will be zero, so this bond is a nonpolar covalent bond.
FF bond in the fluorine molecule (F 2 )
This example highlights the fact that the electronegativity of an atom does not matter, but the difference in electronegativities of the two atoms that form a bond to know if the bond will be nonpolar covalent or not.
Fluorine is the most electronegative element in the periodic table, so it tends to strip electrons from the other elements to form polar or ionic bonds.
However, when a fluorine atom binds to another equal to it, neither of them can remove the electrons from the other (there is no difference in electronegativity), so they have no choice but to share them equally and form, thus, a nonpolar covalent bond.
The OO bonds in the ozone molecule (O 3 )
As in the case of the fluorine molecule, oxygen is also a very electronegative element. However, by forming bonds with other oxygen atoms, it forms nonpolar covalent bonds. Such is the case with the ozone molecule.
In this case, the central oxygen atom is linked to two other oxygen atoms by means of nonpolar or nonpolar covalent bonds.
NN bond in the nitrogen molecule (N 2 )
The nitrogen molecule contains a nonpolar covalent bond, in which each nitrogen atom shares its three unpaired valence electrons with the other.
For this reason, both atoms share a total of three pairs of electrons, thus forming a triple covalent bond.
CH bonds in the methane molecule (CH 4 )
Methane is an example of a nonpolar covalent bond formed between atoms of different elements, in this case carbon and hydrogen.
The electronegativity difference between the two elements is 0.4 which places this bond right on the border between nonpolar and polar bonds.
C = C bond in the ethylene molecule (C 2 H 4 )
The ethylene molecule, also called ethene, has a total of five bonds. Four CH bonds and one C = C double bond. In both cases, the bonds correspond to nonpolar or nonpolar covalent bonds.