The correct order of dipole moments for molecules NH3, H2S, CH4 and HF, is:
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Quick Answer
Option D
HF > NH3 > H2S > CH4
— Concept: Dipole moment is a measure of the polarity of a chemical bond or a molecule.Step-by-step solution
1AnswerD·
Concept: Dipole moment is a measure of the polarity of a chemical bond or a molecule. It arises from the difference in electronegativity between bonded atoms and the molecular geometry. A larger difference in electronegativity and an asymmetrical molecular geometry lead to a higher dipole moment.
Why (D) is correct:
- HF: Hydrogen fluoride has a very high electronegativity difference between H (2.20) and F (3.98). It is a linear molecule, so the bond dipole moment is also the molecular dipole moment. This large difference makes HF highly polar.
- NH\u2083: Ammonia has a trigonal pyramidal geometry with a lone pair on nitrogen. The N-H bonds are polar due to the electronegativity difference between N (3.04) and H (2.20). The bond dipoles and the lone pair dipole add up vectorially, resulting in a significant net dipole moment.
- H\u2082S: Hydrogen sulfide has a bent geometry with two lone pairs on sulfur. The S-H bonds are polar due to the electronegativity difference between S (2.58) and H (2.20), but this difference is smaller than in NH\u2083 or HF. The bond dipoles and lone pair dipoles add up, but the overall polarity is less than NH\u2083.
- CH\u2084: Methane has a tetrahedral geometry. Although the C-H bonds are slightly polar (electronegativity difference between C (2.55) and H (2.20)), the symmetrical arrangement of these bonds in a tetrahedral structure causes the individual bond dipoles to cancel each other out. Therefore, CH\u2084 has a net dipole moment of zero.
Based on these considerations, the correct order of dipole moments is HF > NH\u2083 > H\u2082S > CH\u2084.
Option Analysis:
- A) CH\u2084 > H\u2082S > NH\u2083 > HF: Incorrect. CH\u2084 has zero dipole moment, and HF has the highest.
- B) H\u2082S > NH\u2083 > HF > CH\u2084: Incorrect. HF and NH\u2083 have higher dipole moments than H\u2082S.
- C) NH\u2083 > HF > CH\u2084 > H\u2082S: Incorrect. HF has a higher dipole moment than NH\u2083, and CH\u2084 has zero dipole moment.
- D) HF > NH\u2083 > H\u2082S > CH\u2084: Correct, as explained above.
Correct Answer: (D)
HF > NH3 > H2S > CH4