Question

Which orbital is used by oxygen atom to form a sigma bond with other oxygen atom in ${\mathrm{O}}_2$ molecule? (1) sp hybrid orbital (2) ${\mathrm{sp}}^2$ hybrid orbital (3) ${\mathrm{sp}}^3$ hybrid orbital (4) pure p-orbital

Short answer

The sigma bond in ${\text{O}}_2$ is formed using the ${\text{sp}}^2$ hybrid orbital.

Step-by-step solution

Understand the oxygen-oxygen bond in ${\text{O}}_2$ molecule

In an oxygen molecule (${\text{O}}_2$), two oxygen atoms form a double bond. One of these bonds is a sigma ($\text{σ}$) bond and the other is a pi ($\text{π}$) bond.

Identify the hybridization state of oxygen atoms in ${\text{O}}_2$

Each oxygen atom in ${\text{O}}_2$ undergoes ${\text{sp}}^2$ hybridization. This is because ${\text{sp}}^2$ hybridization allows for the formation of a sigma bond and also provides one unhybridized p-orbital needed for the pi bond.

Determine the orbital used for the sigma bond

During ${\text{sp}}^2$ hybridization, one $2s$ and two $2p$ orbitals mix to form three ${\text{sp}}^2$ hybrid orbitals. The sigma bond between the two oxygen atoms is formed using one of these ${\text{sp}}^2$ hybrid orbitals.

Conclusion

Therefore, the sigma bond in the ${\text{O}}_2$ molecule is formed using the ${\text{sp}}^2$ hybrid orbital.

Key concepts

Orbital Hybridization

Orbital hybridization is a key concept in understanding how atoms bond together to form molecules. It involves the mixing of atomic orbitals to create new hybrid orbitals, which can then participate in bonding. This mixing process happens because atoms strive to achieve the lowest possible energy state, and hybrid orbitals often offer a more stable configuration compared to pure atomic orbitals. When atoms like oxygen form bonds, they tend to undergo hybridization to achieve this stability.
For instance, in an ${\text{O}}_2$ molecule, each oxygen atom undergoes ${\text{sp}}^2$ hybridization. This hybridization involves the combination of one $2s$ and two $2p$ orbitals to form three ${\text{sp}}^2$ hybrid orbitals. These hybrid orbitals are then used to form stronger and more stable bonds between the atoms.
Understanding the concept of orbital hybridization can help you predict the geometry and bond angles in molecules. This concept is fundamental to mastering more complex topics in chemistry.

Sigma and Pi Bonds

In the ${\text{O}}_2$ molecule, two types of covalent bonds are present: sigma ($\text{σ}$) bonds and pi ($\text{π}$) bonds.

Sigma ($\text{σ}$) Bonds:
These are the strongest type of covalent bond and are formed by the direct overlap of orbitals. The electron density in a sigma bond is concentrated along the axis connecting the two bonding nuclei. In ${\text{O}}_2$, the sigma bond is formed using one of the ${\text{sp}}^2$ hybrid orbitals from each oxygen atom.

Pi ($\text{π}$) Bonds:
These bonds are formed when parallel p-orbitals overlap sideways. In ${\text{O}}_2$, after the formation of the sigma bond, each oxygen atom has an unhybridized p-orbital left, which are perpendicular to the internuclear axis. These unhybridized p-orbitals overlap side-by-side to form a pi bond. The electron density in a pi bond is concentrated above and below the plane of the nuclei.
Understanding the distinction between sigma and pi bonds is crucial for grasping the nature of multiple bonds in molecules. Sigma bonds provide the framework, while pi bonds add additional strength and rigidity.

sp2 Hybrid Orbitals

The ${\text{sp}}^2$ hybrid orbitals are formed by the combination of one $2s$ orbital and two $2p$ orbitals from an atom. In the case of an oxygen atom in the ${\text{O}}_2$ molecule, this process creates three equal-energy hybrid orbitals oriented in a trigonal planar arrangement.
These ${\text{sp}}^2$ hybrid orbitals are essential in the formation of sigma bonds. Each oxygen atom in ${\text{O}}_2$ employs one of its ${\text{sp}}^2$ hybrid orbitals to form a sigma bond with the other oxygen atom. The remaining two ${\text{sp}}^2$ hybrid orbitals on each oxygen atom hold lone pairs of electrons, which do not participate directly in bonding but influence the molecule's shape.
The unhybridized $2p$ orbital that remains after ${\text{sp}}^2$ hybridization is used to form the pi bond. This unhybridized orbital overlaps with the corresponding unhybridized orbital from the other oxygen atom, creating the double bond characteristic of oxygen molecules.
Thus, ${\text{sp}}^2$ hybridization plays a pivotal role in the structure and bonding of oxygen in the ${\text{O}}_2$ molecule. It provides the necessary orbitals for both sigma and pi bonding, leading to a stable double-bonded framework.