Question

Discuss valence bond theory in context of \(\mathrm{H}_{2}\) molecule.

Short answer

The Valence Bond Theory explains the formation of an \(\mathrm{H}_{2}\) molecule by the overlap of 1s orbital of two hydrogen atoms, which results in a new molecular orbital that contains the shared pair of electrons. This overlap lowers the overall energy state, providing stability to the \(\mathrm{H}_{2}\) molecule.

Step-by-step solution

Valence Bond Theory

Valence Bond Theory is a theory that explains chemical bonding between atoms forming a bond by overlapping with each other in their atomic or hybrid orbits. Essentially, the atomic orbitals of the bonding atom mix to form a new 'molecular orbital' that contains the electron pair which is shared between the atoms.

Application to Hydrogen Atoms

Single hydrogen atom has one electron in its 1s orbital. For \(\mathrm{H}_{2}\) molecule, the 1s orbital of both the hydrogen atoms overlap with each other due to their vicinity.

Orbital Overlap

In the process of this orbital overlap, two hydrogen atoms share their atomic electrons and hence are connected by a covalent bond. The overlapping orbital area, where the two electrons reside, forms a molecular orbital - representing the formation of \(\mathrm{H}_{2}\) molecule.

Result of Overlap

The orbital overlap results in a lower overall energy state, providing stability to the molecule and thereby explaining the existence of \(\mathrm{H}_{2}\) molecule according to the Valence Bond Theory.

Key concepts

Chemical Bonding

Chemical bonding is the fundamental concept that explains how atoms combine to form compounds. It's an attraction between atoms that enables the formation of chemical substances containing two or more atoms. The bond formation releases energy and results in a stable electronic arrangement for the bonded atoms.

The different types of chemical bonds include ionic, covalent, and metallic bonds. Covalent bonding, which Valence Bond Theory (VBT) primarily deals with, involves the sharing of electron pairs between atoms. This sharing allows each atom to gain the electrons it requires to obtain a stable electron configuration reminiscent of the noble gases.

Molecular Orbital

When atoms bond to form molecules, their atomic orbitals, the regions in space where the probability of finding electrons is highest, combine to create molecular orbitals. Molecular orbitals are the conceptual regions within a molecule where shared electrons reside.

A molecular orbital can be bonding, antibonding, or non-bonding, and it can accommodate a maximum of two electrons with opposite spins. The formation of molecular orbitals is central to molecular orbital theory, which describes how electrons are distributed in a molecule and determines the chemical and physical properties of substances.

Orbital Overlap

Orbital overlap is a key concept in covalent bonding as per Valence Bond Theory. For a covalent bond to form between two atoms, their orbitals must overlap sufficiently to allow for the sharing of electrons.

The extent of overlapping influences the strength and characteristics of the bond. A greater overlap results in a stronger bond, which is why the bond length decreases as the bond order increases. According to VBT, the directional nature of orbital overlap is responsible for the shape and geometry of molecules.

Covalent Bond

A covalent bond is a strong chemical bond formed through the sharing of one or more pairs of electrons between two atoms in a molecule. This sharing allows each atom to fill its outermost electron shell, achieving a more stable arrangement.

Covalent bonds can be single, double, or triple, depending on the number of shared electron pairs. Valence Bond Theory helps explain these bonds by assuming that electron-pair bonds form between atoms through the overlap of their half-filled atomic orbitals.

Hydrogen Molecule

The hydrogen molecule \(\mathrm{H}_{2}\) serves as the simplest model for explaining covalent bonding. In its diatomic form, two hydrogen atoms share their single electrons, resulting in a covalent bond. According to VBT, the 1s atomic orbitals of each hydrogen atom overlap to create a filled bonding molecular orbital. This overlap accounts for the strong bond holding the hydrogen atoms together in a molecule, illustrating the fundamental principles of chemical bonding.

This bonding results in a stable electron configuration and a reduction in potential energy, which is why \(\mathrm{H}_{2}\) exists as a stable diatomic gas under normal conditions. Understanding the formation of the hydrogen molecule is a stepping stone to comprehending more complex bonding scenarios.