Question

What is the definition of bond polarity?

Answer 1

To define bond polarity, we first need to know what kind of compounds show bond polarity. Bond polarity usually occurs in compounds in which the atoms are either bonded by ionic bonds i.e., ionic compounds, or are bonded by polar covalent bonds i.e., polar covalent compounds.

Complete answer:
In both ionic compounds and polar covalent compounds, the electron pairs are not shared equally between the two bonded atoms.
In ionic compounds, for example, in lithium chloride (LiCl), the electron in the 2s orbital of the lithium atom is stripped from the lithium atom and is included in the electronic structure of the chlorine atom to fulfill its outermost electron shell.
Also, in polar covalent compounds, for example in hydrochloric acid (HCl), there exists an electronegative difference between the hydrogen atom and the chlorine atom, and the more electronegative atom i.e., chlorine attracts the electron which is shared towards itself.
Since there is a non-uniformity in the sharing of electrons between the bonded atoms of the molecule, the more electronegative atom forms a partial negative charge in polar covalent compounds and negative charge in ionic compounds whereas the less electronegative atoms form a partial positive charge in polar covalent compounds and positive charge in ionic compounds.
This leads to the formation of polar bonds and hence the molecule shows bond polarity.
The bond polarity in a molecule is the measure of the dipole moment of the entire molecule.
$\mu =e\times d$
Where $\mu$ is the bond dipole, e is the charge and d is the distance between the bonded atom's nuclei.
Since the molecule is neutral, the charge is the magnitude of either the negative or positive charge.

Note:
It should be noted that since a nonpolar covalent compound is formed between two nonmetals having comparable electronegativities, the electrons are shared uniformly between the atoms of a molecule, and hence bond polarity is negligible in a nonpolar covalent compound.