Question

What is the dipole moment of $N{H_3}$?

Answer 1

Dipole moment of a molecule is given by the formula$\mu = \partial .d$. Where $\mu$ is strength of the dipole moment, $\partial$ is the amount of charge at either end of the dipole and $d$ is the distance between these charges.

Complete answer:
By looking at a molecule it is always feasible to calculate its dipole moment. Therefore we can apply the above given formula when the strength and distance of the charges are known. So what do we do when we don’t have the following formula? For that let’s understand what is a dipole moment and what causes a dipole moment.
Dipole moment is a measure of the polarity of a chemical bond between two atoms in a molecule. It involves the concept of electric dipole moment, which is a measure of separation of negative and positive charge in a system.
The main cause of dipole moment is the separation of charges. In a molecule the atoms that are bonded together have certain electronegative differences between them. For that we must know the polarity or polar character of a compound. Polarity is given by the development of positive and negative charge due to electronegativity differences. A more electronegative atom pulls the electron towards it than the one which has less electronegativity.
Now that we are familiar with all these concepts let’s find out the dipole moment of $N{H_3}$
Remember we are finding the overall dipole moment of the molecule not its exact value which is $1.4D$
In the molecule $N{H_3}$ nitrogen is more electronegative than hydrogen atom. Due to this character nitrogen will pull the electrons from hydrogen towards itself. This results in development of negative charge on nitrogen and positive charge on hydrogen. This results in a dipole moment from $H - N$.

Note:
Electronegativity is the measure of an atom’s ability to attract shared electrons itself. On a periodic table, electronegativity generally increases as we move from left to right across a period and decreases as we move down the groups.