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Explain the following: (i) Why is ethylene a planar molecule and acetylene a linear molecule? (ii) Why does bond length decrease in the order? C -C gt C=C gt C-=C (iii) The boiling point of methanol is 66^(@)C and that of methyl mercaptan is 6^(@)C whereas the boiling points of diethyl ether an diethyl sulphide are 35^(@)C and 92^(@)C respectively. (iv) ethanol boils at higher temperature than ethylamine inspite of the fact that both have nearly same molecular masses. (v) What effect should the following resonance of vinyl chloride have on its dipole moment? CH_(2)=CH-CI harr overset(-)(CH_(2))-CH=overset(+)(CI) (vi) The central carbon-carbon bond in 1,3-butadiene is shorter than that of n-butane. (vii) What property of carbon accounts for the occurrence of large number of its compounds? (viii) The C-CI bond is polar while C CI_(4) is non-polar. (ix) Explain the factor on which polarity of bond depends. (x) The CI atom has same electronegativity as nitrogen but it does not form effective hydrogen bonding.

Answer»


Answer :(i) In ethylene each carbon atom undergoes `sp^(2)`-hybridization while in acetylene each carbon undergoes sp-hybridization; (ii) As the s-CHARACTER increases in the hybridized orbitals, greater overlapping occurs with the shortening of bond length (iii) `CH_(3)OH` has higher boiling point than `CH_(3)SH` due to hydrogen BONDING. Diethyl sulphide has higher boiling point than diethyl ether due to large molecular mass (iv) Oxygen being more electronegative than nitrogen FORMS stronger hydrogen bond than the latter, (v) Resonance decreases the dipole moment of vinyl chloride as the positive charge on chloride and a negative charge on carbon oppose each other; (vi) 1,3-butadiene has `sp^(2)-sp^(2)C-C` bond length, while n-butane has `sp^(3)-sp^(3)C-C` bond length. More is 's' character in hybridization , lesser is bond length; (vii) (a) catenation, (b) carbon can link with other carbona tom with single, double and triple bonds. It can form bonds with other atoms also, (c) isomerism; (viii) The dipole moment of `C CI_(4)` is zero inspite of four similar polar `(C-CI)` bonds on account of symmetrical structure; (ix) The polarity of bond depends upon electronegativity difference of two atoms involved in COVALENCE; (x) The size of CI atom is large as compared to nitrogen and so it pulls the shared pair of electron from hydrogen atom less effectively and thus it does not POSSES appreciable partial charge to show hydrogen bonding.


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