Multiple Choice
Which of the following Lewis electron-dot diagrams represents the molecule that is the most polar?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following best describes the molecular polarity of NH_3 (ammonia)?
A
NH_3 is a polar molecule due to its trigonal pyramidal shape and lone pair on nitrogen.
B
NH_3 is polar only in the solid state.
C
NH_3 is nonpolar because its molecular geometry is linear.
D
NH_3 is a nonpolar molecule because all the N-H bonds are identical.
Verified step by step guidance1
Identify the Lewis structure of NH_3 (ammonia). Nitrogen is the central atom bonded to three hydrogen atoms, and it has one lone pair of electrons.
Determine the molecular geometry using VSEPR theory. With three bonding pairs and one lone pair, the shape of NH_3 is trigonal pyramidal, not linear or planar.
Consider the electronegativity difference between nitrogen and hydrogen. Nitrogen is more electronegative, so each N-H bond is polar with a dipole moment pointing toward nitrogen.
Analyze the overall molecular polarity by combining the bond dipoles. Because of the trigonal pyramidal shape and the lone pair, the dipoles do not cancel out, resulting in a net dipole moment.
Conclude that NH_3 is a polar molecule due to its trigonal pyramidal shape and the presence of a lone pair on nitrogen, which causes an uneven distribution of electron density.
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