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1

AIPMT 2011 Prelims

The correct order of increasing bond length of C $$-$$ H, C $$-$$ O, C $$-$$ C and C$$=$$C is
A
C $$-$$ H < C$$=$$C < C $$-$$ O < C $$-$$ C
B
C $$-$$ C < C$$=$$C < C $$-$$ O < C $$-$$ H
C
C $$-$$ O < C $$-$$ H < C $$-$$ C < C$$=$$C
D
C $$-$$ H < C $$-$$ O < C $$-$$ C < C$$=$$C

Explanation

Increasing order of bond length is

$$\mathop {C - H}\limits_{107\,pm} < \mathop {C = C}\limits_{134\,pm} < \mathop {C - O}\limits_{141\,pm} < \mathop {C - C}\limits_{134\,pm}$$
2

AIPMT 2011 Prelims

Which of the following has the minimum bond length ?
A
O2+
B
O2$$-$$
C
O22$$-$$
D
O2

Explanation

Electronic configuration
O2 : $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2{\pi ^*}2p_y^1{\pi ^*}2p_z^1$$

Bond order = $${1 \over 2}\left( {8 - 4} \right)$$ = 2

O2+ : Bond order = $${1 \over 2}\left( {8 - 3} \right)$$ = 2.5

O2- : Bond order = $${1 \over 2}\left( {8 - 5} \right)$$ = 1.5

O22- : Bond order = $${1 \over 2}\left( {8 - 6} \right)$$ = 1

As bond order increases, bond length decreases.
3

AIPMT 2010 Mains

In which of the following molecules the central atom does not have sp3 hybridization?
A
CH4
B
SF4
C
BF4$$-$$
D
NH4+

Explanation

For neutral molecules

No. of electron pairs = No. of atoms bonded to it + 1/2[Gp. no. of central atom - Valency of central atom]

$$\therefore$$For CH4, no. of e- pairs = 4 + 1/2[4 - 4] = 4 (sp3 hybridisation)

For SF4, no. of e- pairs = 4 + 1/2[6 - 4] = 5 (sp3d hybridisation)

and For ions,

No. of electron pairs = No. of atoms bonded to it + 1/2[Gp. no. of central atom - Valency of central atom $$\pm$$ No. of electrons]

$$\therefore$$For BF4-, no. of e- pairs = 4 + 1/2[3 - 4 + 1] = 4 (sp3 hybridisation)

For NH4+, no. of e- pairs = 4 + 1/2[5 - 4 - 1] = 4 (sp3 hybridisation)
4

AIPMT 2010 Mains

Some of the properties of the two species, $$NO_3^ -$$ and $${H_3}{O^ + }$$ are described below. Which one of them is current?
A
Dissimilar in hybridization for the central atom with different structures.
B
Isostructural with same hybridization for the central atom.
C
Isostructural with different hybridization for the central atom
D
Similar in hybridization for the central atom with different structures.

Explanation

No. of electron pairs = No. of atoms bonded to it + 1/2[Gp. no. of central atom - Valency of central atom $$\pm$$ No. of electrons]

For NO3- = 3 + 1/2[5 - 6 + 1] = 3 (sp2 hybridisation)

For H3O+ = 3 + 1/2[6 - 3 - 1] = 4 (sp3 hybridisation)

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