1st Year

Matric, FSc, A/O Level, MDCAT/NUMS and Supplementary Exams Prep with Dr.Sadaqat Baloch

Test: Chemistry MDCAT                                                    Chemical Bonding

01 Encircle The best Option.

1. Which among the following has the shortest C-C bond length?

(a) Ethene

(b) Ethane

(c) Benzene

(d) Ethyne

2. The oxygen molecule is paramagnetic. It can be explained by

(a) Resonance

(b) Hybridisation

(c) Valence bond theory

(d) Molecular orbital theory

3. Find the paramagnetic species

(a) CN^–

(b) NO⁺

(c) CO

(d) O₂^–

4. Find the diamagnetic species

(a) H₂

(b) H₂^–

(c) He₂⁺

(d) H₂⁺

5. Which of the following pairs has the same bond order?

(a) O₂⁺, NO⁺

(b) N₂, O₂

(c) O₂^2-, B₂

(d) NO, CO

6. Each P of P₄O₁₀is attached to how many oxygen atoms?

(a) 3

(b) 2.5

(c) 2

(d) 4

7. When O₂changes to O₂^–, the electron goes to which of the orbitals?

(a) 𝜋 orbital

(b) 𝜎 orbital

(c) 𝜋^* orbital

(d) 𝜎^* orbital

8. O-O bond length is minimum in

(a) O₂^–

(b) O₂

(c) O₂⁺

(d) O₂^2-

9. Which of the following is not paramagnetic?

(a) CO

(b) N₂⁺

(c) NO

(d) O₂^–

10. Find the molecule having the highest bond order

(a) O₂⁺

(b) O₂^–

(c) O₂^2-

(d) O₂

Answer

1. (d)	2. (d)	3. (d)	4. (a)	5. (c)
6. (d)	7. (c)	8. (c)	9. (a)	10. (a)

 

 

 

11. Combination of two atomic orbitals results in the formation of two molecular orbitals namely _________
    a) one bonding and one non-bonding orbital
    b) two bonding orbitals
    c) two non-bonding orbitals
    d) two bonding and non-bonding orbitals

Answer: a
Explanation: F. Hund and R.F. Mullikan proposed Molecular orbital theory in the year 1932. According to this theory, the combination of two atomic orbitals results in the formation of two molecular orbitals namely one bonding and one non-bonding orbital.

12. Stability increases, as the energy ___________
    a) increases
    b) doesn’t change
    c) decreases
    d) increases and then decreases

Answer: c
Explanation: As the stability increases, the energy of that substance decreases. The higher the energy, the less stable the molecule. So stability is inversely proportional to the energy. This can be seen in any part of the universe

13. Which of the following is a condition for the combination of atomic orbitals?
    a) Combining atomic orbitals need not have equal energy
    b) Combining atomic orbitals must have symmetry as per molecular axis
    c) Combining atomic orbitals must overlap to a minimum extent
    d) For combining atomic orbitals, X-axis should be taken as a molecular axis

Answer: b
Explanation: Combining atomic orbitals must have symmetry as per molecular axis is true. The corrected statements are combining atomic orbitals must have equal energy, must overlap to the maximum extent and Z-axis should be taken as the molecular axis.

14. Sigma molecular orbitals are not symmetrical around the bonding axis.
    a) True
    b) False

Answer: b
Explanation: According to the nomenclature, sigma molecular orbitals are symmetrical around the bonding axis and the pi molecular orbitals are not symmetrical around the bonding axis. So the given statement is false.

15. Which of the bonding orbital has greater energy comparatively?
    a) Both Bonding molecular orbital and Anti-bonding molecular orbital have the same energy
    b) The energy of Bonding molecular orbital and Anti-bonding molecular orbital depends on the situation
    c) Bonding molecular orbital
    d) Anti-bonding molecular orbital

Answer: d
Explanation: An electron that enters bonding orbitals stabilizes the molecule as it’ in between two nuclei. Whereas when an electron is entered into the anti-bonding orbital, it needs to pull an electron away from the nucleus.

16. Take N_Aas the number of Anti-bonding molecular orbitals and N_Bas the number of Bonding molecular orbitals. The molecule is stable when N_A ____________ N_B.
    a) is greater than
    b) is equal to
    c) is less than
    d) is greater than or equal to

Answer: c
Explanation: When a molecule consists both bonding molecular orbitals and anti-bonding molecular orbitals, the higher the number of bonding orbitals, the more the bonding influence and the more stable the molecule will be and vice-versa.

17. What’s the bond order of Oxygen?
    a) 3
    b) 2
    c) 1
    d) 0

Answer: b
Explanation: The formula of bond order is given by ¹⁄₂(N_B – N_A) When N_B is bonding orbitals and N_A is the number of anti-bonding orbitals. In Oxygen, bond order = 1/2(10-6) = 2. When it’s zero the molecule cannot be formed.

18. What do you think is the relationship between bond order and bond length?
    a) Directly proportional
    b) Indirectly proportional
    c) No relation
    d) Cannot predict

Answer: b
Explanation: The bond length has defined the distance between two atoms in a molecule. The bond order depends on the bond length between two atoms in a molecule. As the bond length increases the bond decreases and vice-versa.

19. Which of the following molecule is not true about paramagnetic molecules?
    a) Attracted by the magnetic field
    b) A molecular orbital is singly occupied
    c) An example is oxygen molecule
    d) Repelled by the magnetic field

Answer: d
Explanation: Paramagnetic molecules are attracted by the magnetic field and orbitals are singly occupied. O₂ is an example. Whereas diamagnetic molecules are repelled by the magnetic field, so the option is wrong.

20. The relative energies of molecular orbitals in increasing order have been found to be as follows.
    (σ_1s) < (σ*_1s) < (σ_2s) < (σ*_2s) < [(π_2py)(π_2pz)] < (σ _2px) < [(π*_2py)(π*_2pz)] < (σ*_2px)
    a) For O₂to Ne₂
    b) For H₂to N₂
    c) For H₂ to Ne₂
    d) For N₂ to Ne₂

Answer: b
Explanation: The relative energies of molecular orbitals in increasing order have been found to be (σ_1s) < (σ*_1s) < (σ_2s) < (σ*_2s) < [(π_2py)(π_2pz)] < (σ_2px) < [(π*_2py)(π*_2pz)] < (σ*_2px) for H₂ to N₂ only.

 

 

21.

Which statement is false? A sigma molecular orbital

(a) may result from overlap of p atomic orbitals perpendicular to the molecular axis (side-on).

(b) may result from overlap of p atomic orbitals along the molecular axis (head-on).

(c) may result from overlap of two s atomic orbitals.

(d) may result from overlap of one s and one p atomic orbitals.

(e) may be either bonding or antibonding.

22.

Carbon monoxide has ten bonding electrons and four antibonding electrons. Therefore it has a bond order of

(a) 3

(b) 7

(c) 1

(d) 5/2

(e) 2

23.

Which of the following is the correct electron configuration for C₂?

(a) _1s² _2s² _2py² *_1s² *_2s² *_2py²

(b) _1s² *_1s² _2s² *_2s² _2py² *_2pz¹ _2p¹

(c) _1s² *_1s² _2s² *_2s² _2py² _2pz²

(d) _1s² *_1s² _2s² *_2s² _2py¹ _2pz¹

(e) _1s² *_1s² _2s² *_2s² _2py¹ *_2py¹ _2pz¹ *_2pz¹

24.

What is the correct electron configuration for the molecular ion, B₂⁺?

(a) _1s² *_1s² _2s² *_2s² _2p²

(b) _1s² *_1s² _2s² *_2s² _2py²

(c) _1s² *_1s² _2s² *_2s² _2py² _2pz¹

(d) _1s² *_1s² _2s² *_2s² _2p¹ _2py¹

(e) none of the above.

25.

Draw the molecular orbital diagram for the molecular ion, N₂⁺. The number of electrons in the

 _2p molecular orbital is:

(a) 0

(b) 1

(c) 2

(d) 3

(e) 4

26.

What is the bond order in O₂⁺?

(a) 3.5

(b) 2.0

(c) 1.5

(d) 2.5

(e) 0

27.

Draw the molecular orbital diagram for B₂. The number of unpaired electrons in the B₂ molecule is _____.

(a) zero

(b) 1

(c) 2

(d) 3

(e) 4

28.

Which one of the following statements is false?

(a) Valence bond theory and molecular orbital theory can be described as two different views of the same thing.

(b) When one considers the molecular orbitals resulting from the overlap of any two specific atomic orbitals, the bonding orbitals are always lower in energy than the antibonding orbitals.

(c) Molecular orbitals are generally described as being more delocalized than hybridized atomic orbitals.

(d) One of the shortcomings of molecular orbital theory is its inability to account for a triple bond in the nitrogen molecule, N₂.

(e) One of the shortcomings of valence bond theory is its inability to account for the paramagnetism of the oxygen molecule, O₂.

29.

Antibonding molecular orbitals are produced by

(a) constructive interaction of atomic orbitals.

(b) destructive interaction of atomic orbitals.

(c) the overlap of the atomic orbitals of two negative ions

(d) all of these

(e) none of these

30.

Which statement regarding stable heteronuclear diatomic molecules is false?

(a) All have bond orders greater than zero.

(b) The antibonding molecular orbitals have more of the character of the more electropositive element than of the more electronegative element.

(c) Their molecular orbital diagrams are more symmetrical than those of homonuclear diatomic molecules.

(d) The bonding molecular orbitals have more of the character of the more electronegative element than of the less electronegative element.

(e) The greater is the difference in energy between two overlapping atomic orbitals, the more polar the resulting bond is, due to electrons occupying the resulting bonding molecular orbital.

Answers:

21. (a)22. (a) 23. (c) 24. (e) 25. (b) 26. (d) 27. (c) 28. (d) 29. (b) 30. (c)

 

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