What are the Types of covalent bond? A covalent chemical bond occurs in molecules between atoms due to the formation of common electron(What are valence electrons?) pairs. The type of covalent bond can be understood as both the mechanism of its formation and the polarity of the bond. In general, covalent bonds can be classified as follows:
- According to the mechanism of formation, a covalent bond can be formed by an exchange or donor-acceptor mechanism.
- The polarity of a covalent bond can be non-polar or polar.
- According to the multiplicity of the covalent bond, it can be single, double or triple.
This means that a covalent bond in a molecule has three characteristics. For example, in a molecule of hydrogen chloride (HCl), a covalent bond is formed by the exchange mechanism, it is polar and single. In the ammonium cation (NH 4 + ), a covalent bond between ammonia (NH 3 ) and a hydrogen cation (H + ) is formed by the donor-acceptor mechanism, in addition, this bond is polar, is single. In the nitrogen molecule (N 2 ), the covalent bond is formed by the exchange mechanism, it is non-polar, it is triple.
In the exchange mechanism for the formation of a covalent bond, each atom has a free electron (or several electrons). Free electrons of different atoms form pairs in the form of a common electron cloud.
With the donor-acceptor mechanism for the formation of a covalent bond, one atom has a free electron pair, while the other has an empty orbital. The first (donor) gives a pair for common use with the second (acceptor). So in the ammonium cation, nitrogen has a lone pair, and the hydrogen ion has a free orbital.
A nonpolar covalent bond is formed between atoms of the same chemical element. So in the molecules of hydrogen (H 2 ), oxygen (O 2 ) and others, the bond is non-polar. This means that the common electron pair equally belongs to both atoms, since they have the same electronegativity.
A polar covalent bond is formed between atoms of different chemical elements. A more electronegative atom displaces an electron pair towards itself. The greater the difference in the electronegativity of the atoms, the more the electrons will be displaced, and the bond will be more polar. So in CH 4 , the shift of common electron pairs from hydrogen atoms to carbon atom is not so large, since carbon is not much more electronegative than hydrogen. However, in hydrogen fluoride, the HF bond is highly polar, because the difference in electronegativity between hydrogen and fluorine is significant.
A single covalent bond is formed if the atoms share one electron pair, double – if two, triple – if three. An example of a single covalent bond can be hydrogen molecules (H 2 ), hydrogen chloride (HCl). An example of a double covalent bond is an oxygen molecule (O 2 ), where each oxygen atom has two unpaired electrons. An example of a triple covalent bond is a nitrogen molecule (N 2 ).