Question

Which of the following has zero dipole moment?
A. \[B{F_3}\]
B. BeClBr
C. \[C{H_2}C{l_2}\]
D. COS

Answer 1

Hint: The dipole moment is formed when there is electronegativity difference between the atoms. When the moment of dipole is toward the pair of electrons, then the dipole moment is larger.

Complete step by step answer:
A. \[B{F_3}\]: In boron trifluoride, the structure is trigonal planar geometry. The fluorine is the most electronegative atom, so the movement of dipole is towards the fluorine atom. As the magnitude is the same for the two B-F bonds which are opposite to the third B-F bond, it will cancel the dipole of the third B-F bond and as a result the dipole will be zero.
The structure of boron trifluoride is shown below.

B. BeClBr
BeClBr forms a linear geometry as the two substituents attached are not same.
C. \[C{H_2}C{l_2}\]
In \[C{H_2}C{l_2}\], the chlorine atom is the most electronegative as compared to carbon and then hydrogen. The dipole moment will be towards the right side C-Cl and in vertical direct C-Cl. Both the dipoles will not be canceled out.
The structure is shown below.

D. COS
The molecule COS has dipole as it is linear and asymmetric in nature. The oxygen atom is more electronegative than the Sulphur atom, so the oxygen will attract more electrons as compared to Sulphur. The two dipoles do not cancel out each other.

So, the correct answer is Option A.

Note: Dipole moment takes place when there is a separation of charge into positive ion and negative ion due to unequal attraction of electrons by the two atoms. The dipole moment helps to determine the polarity of the compound.