Question

Does the molecule $OCS$ have a higher or lower dipole moment than $C{S_2}$?
(A) Higher dipole moment than of $C{S_2}$
(B) Lower dipole moment than of $OCS$
(C) Equal dipole moment than $OCS$.
(D) None of the above

Answer 1

Dipole moment can be present in both ionic as well as the covalent bond. Dipole moment will arise when there is a separation of charge. It can also occur when there is a difference in the electronegativity of the two chemically bonded atoms.

Complete step by step answer:
Let us first consider the $C{S_2}$ molecule.
In order to find the dipole moment of $C{S_2}$, we have to first understand the structure of the Carbon disulphide molecule. Carbon will be having a valency of 4 while Sulphur is having a valency of 2. Therefore, two sulphur atoms will be bonding to the carbon atom from each side. Two sulphur atoms will be present at $180^\circ$ from each other.
Hence the bond formed between the Carbon and Sulphur is given below:
$S = C = S$
The molecule will be having sp hybridisation and therefore it will be having a linear shape. In the molecule, the Sulphur is having an electronegativity of 2.58 and for the Carbon is having electronegativity of 2.55. The movement of dipole will be from Carbon to sulphur. As we know that $S = C = S$ is a symmetrical molecule. The individual bond dipole moment is equal in magnitude and opposite in direction. Therefore, this will cancel bond dipole moment on each side and thus will have zero dipole moment.
On the other hand, $OCS$ is an asymmetrical molecule. Like $C{S_2}$, $OCS$ also will be having sp hybridisation and therefore, the structure will be Linear. The electronegativity of Oxygen is 3.5 which is very high compared to Sulphur. Therefore, Polarity of the bond will be in the direction where the electronegativity difference between the atom is more. The electronegativity difference is more in Carbon and Oxygen compared to Carbon and Sulphur. Therefore, the dipole moment in $OCS$ is higher compared to $C{S_2}$ whose dipole moment is zero.

Hence the correct answer is option (A) Higher dipole moment than of $C{S_2}$.

Additional information:
Let us understand the formula for dipole moment.
Dipole moment can be represented as the product of magnitude of charges and the distance between the centres of the positive and the negative charge. The dipole moment can be denoted as $\mu$.
It is given by the formula
${\rm{Dipole moment(\mu ) = Charge(Q) \times Distance of separation(l)}}$
The bond dipole moment arises in a chemical bond between atoms of different electronegativities is given by
$\mu = \delta .d$

Note: - In a polyatomic molecule, the dipole moment is given as the vector sum of the bond dipoles of the molecule.
- Dipole moment is a vector quantity i.e. it will give both magnitude and direction.