Test: Valence Bond Theory - NEET MCQ

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.

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.

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 1s²2s¹2p³.

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.

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.

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.

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.

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.

• Spherical Symmetry: s-orbitals have spherical symmetry, meaning they are symmetrical in all directions around the nucleus. This spherical shape allows the electron cloud to be evenly distributed in all directions, making it nondirectional.


• Small Size: The small size of s-orbitals also contributes to their nondirectional nature. Since they are small, the electron cloud does not extend too far in any particular direction, leading to a uniform distribution of electron density.


• First Orbital: Being the first orbital in the electron configuration, s-orbitals have the simplest shape, a sphere. This simplicity in shape also contributes to their nondirectional nature.


• All of the Above: Taking into account the spherical symmetry, small size, and simplicity of being the first orbital, we can conclude that s-orbitals are nondirectional due to all these factors combined.

• Paramagnetic Nature: The oxygen molecule (O2) is paramagnetic because it has two unpaired electrons in its molecular orbitals.


• Molecular Orbital Theory: According to molecular orbital theory, when two oxygen atoms combine to form O2, a new set of molecular orbitals is formed from the combination of atomic orbitals. These molecular orbitals can be bonding, antibonding, or nonbonding.


• Unpaired Electrons: In the case of O2, the molecular orbitals have two unpaired electrons in the antibonding π* orbitals. This makes O2 paramagnetic as it has unpaired electrons that align with an external magnetic field.


• Explanation: The paramagnetic nature of O2 can be explained by the presence of these unpaired electrons in its molecular orbitals, as predicted by the molecular orbital theory.