This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Molecular Orbital Theory”.
1. If the sign of the wave function is unchanged when the orbital is reflected about its centre, the orbital is ______________
a) Gerade
b) Ungerade
c) Gerade as well as Ungerade
d) None of the mentioned
View Answer
Explanation: If the sign of the wave function is unchanged when the orbital is reflected about its center (i.e., x, y and z are replaced by –x, -y and –z), the orbital is gerade.
2. The filling of molecular orbital takes place according to __________
a) The Aufbau Principle
b) Pauli Exclusion Principle
c) Hund’s rule of maximum multiplicity
d) All of the mentioned
View Answer
Explanation: According to these principles, molecular orbitals are filled in order of increasing energy. Two electrons in the same orbital cannot have the same set of all four quantum numbers identical.
3. Bond Order of O2, F2, N2 respectively are __________
a) +1, +2, +3
b) +2, +3, +1
c) +2, +1, +3
d) +3, +2, +1
View Answer
Explanation: Bond Order=[[Number of electrons in bonding molecular orbital]-[Number of electrons in antibonding molecular orbital]]/2.
4. Arrange the following molecules in decreasing bond length.
a) O2 > O2– > O2+ > O22-
b) O22- > O2– > O2 > O2+
c) O22- > O2– > O2+ > O2
d) O2– > O2+ > O22- > O2
View Answer
Explanation: The bond length is inversely proportional to the bond order. Therefore, the correct is:
O22- > O2– > O2 > O2+.
5. Arrange the following molecules in the order of increasing stability.
a) N2+ < N2 < N2– < N22-
b) N22- < N2– < N2 < N2+
c) N22- < N2– = N2+ < N2
d) N2 < N2+ = N2– < N22-
View Answer
Explanation: The order of stability is directly proportional to the bond order. Therefore, the correct order of stability is N22- < N2– = N2+ < N2.
6. On the basis of molecular orbital theory, select the most appropriate option.
a) The bond order of O2 is 2.5 and it is paramagnetic
b) The bond order of O2 is 1.5 and it is paramagnetic
c) The bond order of O2 is 2 and it is diamagnetic
d) The bond order of O2 is 2 and it is paramagnetic
View Answer
Explanation: Oxygen is paramagnetic in nature and its bond order is 2. It is an exceptional case.
7. Which of the following molecule does not exist due to its zero bond order?
a) H2+
b) He2+
c) He2
d) H2–
View Answer
Explanation: Molecular orbital electronic configuration of He2 molecule = (σ1s)2 (σ*1s)2. Bond order = 0, so He2 molecule does not exist.
8. The relative energies of molecular orbitals in increasing order have been found to be as follows.
(σ1s) < (σ*1s) < (σ2s) < (σ*2s) < [(π2py)(π2pz)] < (σ 2px) < [(π*2py)(π*2pz)] < (σ*2px)
a) For O2 to Ne2
b) For H2 to N2
c) For H2 to Ne2
d) For N2 to Ne2
View Answer
Explanation: The relative energies of molecular orbitals in increasing order have been found to be (σ1s) < (σ*1s) < (σ2s) < (σ*2s) < [(π2py)(π2pz)] < (σ2px) < [(π*2py)(π*2pz)] < (σ*2px) for H2 to N2 only.
9. According to Molecular Orbital Theory, the shape and size of a molecular orbital depends upon _________
a) Shape and size of the combining atomic orbitals
b) Numbers of the combining atomic orbitals
c) Orientation of the combining atomic orbitals
d) All of the mentioned
View Answer
Explanation: The shape and size of a molecular orbital depend upon the shape, size, number and orientation of the combining atomic orbitals.
10. Choose the incorrect statement from the following options.
a) In bonding molecular orbital, electron density is low in the region between the nuclei of bonded atoms
b) The energy of antibonding molecular orbital is higher than that of atomic orbitals from which it is formed
c) Every electron in bonding molecular orbital contributes toward stability of the molecule
d) Antibonding takes place when lobes of atomic orbitals have different signs
View Answer
Explanation: In bonding molecular orbital, the electron density is high in the region between the nuclei of bonded atoms. All the other options are correct. The energy of antibonding molecular orbital is higher than that of atomic orbitals from which it is formed. Every electron in bonding molecular orbital contributes to the stability of the molecule. Antibonding takes place when lobes of atomic orbitals have different signs.
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