Chemistry Multiple Choice Questions on “Valence Bond Theory”.
1. The bond enthalpy of ___________ molecule is 435.8 kJ mol-1.
a) Hydrogen
b) Oxygen
c) Nitrogen
d) Helium
Answer: a
Clarification: The amount of energy that is required to break a chemical bond in a molecule into individual atoms is known as bond enthalpy. 435.8 kJ mol-1 is required to dissociate a hydrogen molecule into two hydrogen atoms.
2. The strength of covalent ___________ extent of overlapping of orbitals.
a) may be or may not be related
b) is independent on
c) is dependent on
d) is not related to
Answer: c
Clarification: As per the concept of valence bond theory, the partial merging of atomic orbitals id knowns as overlapping. The extent of overlapping is directly proportional to the strength of the covalent bond, i.e. it is dependent.
3. What is the electronic configuration of carbon in it’s excited state?
a) 1s22s22p4
b) 1s22s22p3
c) 1s22s22p5
d) 1s22s12p4
Answer: b
Clarification: The electronic configuration of carbon in its ground state is given by 1s22s22p4. When it’s in an excited state, that is when it loses an electron, that would be from 2p-orbital. So the excited state’s electronic configuration is 1s22s22p3.
4. Which type of bond is present between hydrogens in hydrogen molecule?
a) Sigma bond
b) Pi bond
c) Ionic bond
d) Metallic bond
Answer: a
Clarification: The head-on or end to end type of overlapping is present in sigma bond. A sigma bond is a type of covalent bond. It may also be called an axial overlap. In case of the hydrogen molecule, its s-s overlapping.
5. The pi-bond involves __________
a) axial overlapping
b) side-wise overlapping
c) end to end type of overlapping
d) head-on overlapping
Answer: b
Clarification: A pi-bond is a type of covalent bond in which the internuclear axes of the atoms are parallel to each other and for side-wise overlapping. The bond formed here is perpendicular to the internuclear axes.
6. A pi bond is stronger than a sigma bond.
a) True
b) False
Answer: b
Clarification: A sigma bond is always stronger than the pi bond. As we know that the bond strength is decided by the extent of orbital’s overlapping. The extent of overlapping is more in sigma bond than in a pi-bond.
7. A __________ overlap doesn’t result in the formation of a bond.
a) positive
b) negative
c) zero
d) rational
Answer: c
Clarification: Zero overlap means that the orbitals don’t overlap at all. When there is no overlapping the bond formation doesn’t occur. As we all know that the extent of overlapping is dependent on the strength of the bond.
8. A positive overlap is same as ________
a) out-phase overlap
b) negative overlap
c) zero overlap
d) in-phase overlap
Answer: d
Clarification: A positive overlap results in bond formation. When 2 p-orbitals are in phase, both the positive lobes overlap, thus creating a positive overlap and result in the bond formation, thus it is called in-phase overlap.
9. Valence bond theory explains the overlapping of atomic orbitals.
a) True
b) False
Answer: a
Clarification: Valence bond theory was initially introduced by London and Heitler and was developed by Pauling and others. It’s a chemical bonding theory that explains the overlapping the atomic orbitals in order to form chemical bonds between atoms.
10. Which of the following is not a homonuclear diatomic molecule?
a) H2
b) N2
c) O2
d) HCl
Answer: d
Clarification: The molecule that is formed from the same element is known as a homonuclear molecule and the molecule that is made up of 2 atoms is called a diatomic molecule. But HCl is not a homonuclear diatomic molecule as it has different atoms.