Question

22. Identify the compound with the largest dipole moment in the gas phase.

a. Cl₂

b. NaBr

c. HCI

d. CCl₄

e. BrF

Answer 1

The dipole moment is the vector whose absolute value is equal to the difference of electronegativity between the constituents multiplied by the distance seperating them. Hence the magnitude of dipole moment is directly propotional to the difference in the electronegativity between the constituent atoms.

Thus for the homoneuclear molecules there are no dipole moment because there are no change in the dipole moment.. The options (a),(d) are ruled out. For Cl2 the net change in electronegativity is zero .Also in CCl4 the polarities or the bond moments of the C-Cl bonds are moving away from each other imparting no polarity to the molecule.

Amongst (b),(d) and (e) the dipole moment is decided according to the change in electronegativity. The absolute electronegativities of H,F,Cl,Na,Br are 2.20,3.96,3.16,0.93,2.96 respectively. Thus the change in electronegativity for NaBr is nearly 2.03, for HCl is 0.96 ,for BrF is 1.00 approximately. Hence in the gas phase the NaBr has maximum electronegativity difference and thus largest dipole moment.