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Chemical Bonding and Molecular Structure · Question 99

AIPMT 2003MCQEasy📈 Topic in 0% papers+4−1
1

Which one of the following statements is not correct for sigma- and pi- bonds formed between two carbon atoms?

  1. sigma-bond is stronger than a pi-bond.
  2. Bond energies of sigma- and pi-bonds are of the order of 264 kJ/mol and 347 kJ/mol, respectively
  3. Free rotation of atoms about a sigma-bond is allowed but not in case of a pi-bond.
  4. Sigma-bond determines the direction between carbon atoms but a pi-bond has no primary effect in this regard.

Answer

(2) Bond energies of sigma- and pi-bonds are of the order of 264 kJ/mol and 347 kJ/mol, respectively

Solution

As per NCERT, a sigma bond is formed by head-on (axial) overlap, which is larger than the sideways overlap of a pi bond, so a sigma bond is stronger than a pi bond.

⇒ C–C sigma bond energy ≈ 347 kJ mol-1 and C=C bond energy ≈ 611 kJ mol-1

⇒ pi bond energy ≈ 611 - 347 = 264 kJ mol-1

∴ The values in statement (2) are interchanged: sigma ≈ 347 kJ/mol and pi ≈ 264 kJ/mol, so statement (2) is not correct.

Statements (1), (3) and (4) are correct: rotation about a pi bond would break the sideways overlap, and the direction of the C–C bond (bond axis) is fixed by the sigma bond.

Answer: (2)

AIPMT 2003

Keep practising — Chemical Bonding and Molecular Structure

2

Which of the following has p - d bonding?

  1. NO3-
  2. SO32-
  3. BO33-
  4. CO32-
AIPMT 2002
3

In NO3- ion number of bond pair and lone pair of electrons on nitrogen atom are

  1. 2, 2
  2. 3, 1
  3. 1, 3
  4. 4, 0
AIPMT 2002
4

Main axis of a diatomic molecule is z, atomic orbitals px and py overlap to form which of the following orbitals.

  1. molecular orbital
  2. molecular orbital
  3. molecular orbital
  4. No bond will form
AIPMT 2001
5

Which of the following two are isostructural?

  1. XeF2, IF2-
  2. NH3, BF3
  3. CO32-, SO32-
  4. PCl5, ICl5
AIPMT 2001
6

In which of the following bond angle is maximum ?

  1. NH3
  2. NH4+
  3. PCl3
  4. SCl2
AIPMT 2001
7

In X-H Y, X and Y both are electronegative elements. Then

  1. electron density on X will increase and on H will decrease
  2. in both electron density will increase
  3. in both electron density will decrease
  4. on X electron density will decrease and on H will increase.
AIPMT 2001
8

d - p bond present in

  1. CO32-
  2. PO43-
  3. NO3-
  4. NO2-
AIPMT 2000
9

Right order of dissociation energy N2 and N2+ is

  1. N2 > N2+
  2. N2 = N2+
  3. N2+ > N2
  4. none
AIPMT 2000
10

Which species does not exhibit paramagnetism?

  1. N2+
  2. O2-
  3. CO
  4. NO
AIPMT 2000
11

Which compound forms linear polymer due to H-bond?

  1. H2O
  2. NH3
  3. HF
  4. HCl
Out of syllabusAIPMT 2000

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