Question

Identify the option where all four molecules possess a permanent dipole moment at room temperature.

• A. B_F, O₃, SF₆, XeF₆
• B. BeCl₂, CO₂, BCl₃, CHCl₃
• C. SO₂, C₆H₅Cl, H₂Se, BrF₅
• D. NO₂, NH₃, POCl₃, CH₃Cl

Answer 1

Answer: (C), (D)

NO₂, NH₃, POCl₃, CH₃Cl

Dipole moments occur when there is a separation of charge. They can occur between two ions in an ionic bond or between atoms in a covalent bond; dipole moments arise from differences in electronegativity. The larger the difference in electronegativity, the larger the dipole moment. The size of a dipole is measured by its dipole moment ($\mu$).

• We know that the polar character is the separation of negative and positive charges in a compound and the measurement of this polar character of a chemical bond in a molecule or between two atoms is given by the dipole moment.
• We know that the separation of charges will lead to the formation of a dipole moment and the main reason for the development of a dipole moment is the differences in electronegativity between the chemically bonded atoms.

For symmetrical molecule μ = 0

For unsymmetrical molecule μ ≠ 0

An explanation for the correct option:

(C) SO₂, C₆H₅Cl, H₂Se, BrF₅

In this option, all molecules have a nonzero dipole moment and hence they possess a permanent dipole moment.

(d) NO₂, NH₃, POCl₃, CH₃Cl

In this option, all molecules have a nonzero dipole moment and hence they possess a permanent dipole moment.

An explanation for the incorrect option:

(a) BF₃, O₃, SF₆, XeF₆

In this option, the net dipole moment of the molecules BF₃ and SF₆ is zero and hence they do not possess a permanent dipole moment.

(b) BeCl₂, CO₂, BCl₃, CHCl₃

In this option, the net dipole moment of the molecules BeCl_2, BCl_3, and CO₂ is zero and hence they do not possess a permanent dipole moment.

Final Answer: options C and D both are correct because both show zero dipole moment at room temperature.