1
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

Which of the two ions from the list given below that have the geometry that is explained by the same hybridization of orbitals, NO$$_2^ - $$. NO$$_3^ - $$, NH$$_2^ - $$, NH$$_4^ + $$, SCN$$-$$?
A
NO$$_2^ - $$ and NO$$_3^ - $$
B
NH$$_4^ + $$ and NO$$_3^ - $$
C
SCN$$-$$ and NH$$_2^ - $$
D
NO$$_2^ - $$ and NH$$_2^ - $$

Explanation

Ions Hybridisation
$$NO_2^-$$ $$sp^2$$
$$NO_3^-$$ $$sp^2$$
$$NH_2^-$$ $$sp^3$$
$$NH_4^+$$ $$sp^3$$
$$SCN^-$$ sp
2
MCQ (Single Correct Answer)

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
MCQ (Single Correct Answer)

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
MCQ (Single Correct Answer)

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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