Q. 16 Among B−H, C−H, N−H and Si−H bonds in BH₃, CH₄, NH₃ and SiH₄, respectively, the polarity of the bond which is shown INCORRECTLY is
- Bδ+−Hδ−
- Cδ−−Hδ+
- Nδ−−Hδ+
- Siδ−−Hδ+
Bond polarity arises from electronegativity differences between atoms, determining partial charges (δ+ or δ−). This guide analyzes B−H, C−H, N−H, and Si−H bonds to spot the wrong polarity notation.
Correct Answer
The incorrect polarity is Bδ+−Hδ−. Boron holds a partial positive charge (Bδ+−Hδ−) due to lower electronegativity than hydrogen.
Electronegativity Basics
Electronegativity (EN) measures an atom’s pull on electrons: H (2.20), B (2.04), C (2.55), N (3.04), Si (1.90). Bond polarity follows: higher EN atom gets δ−, lower gets δ+.
Option Analysis
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Bδ+−Hδ− (BH₃): EN difference |2.20 – 2.04| = 0.16; B less electronegative, so Bδ+−Hδ− is correct .
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Cδ−−Hδ+ (CH₄): EN difference |2.20 – 2.55| = 0.35; C more electronegative, so Cδ−−Hδ+ is correct .
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Nδ−−Hδ+ (NH₃): EN difference |2.20 – 3.04| = 0.84; N highly electronegative, so Nδ−−Hδ+ is correct .
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Siδ−−Hδ+ (SiH₄): EN difference |2.20 – 1.90| = 0.30; Si less electronegative, so incorrect—should be Siδ+−Hδ− .
Why Si−H is Misrepresented
Silicon (EN 1.90) donates electron density to hydrogen (EN 2.20), making Siδ+ and Hδ−. The option reverses this, showing Siδ−−Hδ+ wrongly.
