Question

What is a sigma bond? How does the overlap of two 1/2 filled 1s orbitals produce a sigma bond?

Answer 1

Hint :Organic molecules, like benzene, are frequently cyclic compounds with one or more rings and are made up of multiple sigma bonds as well as pi bonds. The number of sigma bonds in a molecule is equal to the number of atoms plus the number of rings minus one, according to the sigma bond rule.

Complete Step By Step Answer:
Sigma bonds (bonds) are the strongest form of covalent chemical bond in chemistry. They're made up of atomic orbitals that collide head-on. For diatomic molecules, sigma bonding is most easily characterised using the language and tools of symmetry groups. A $\sigma$ -bond is symmetrical with regard to rotation about the bond axis in this formal method. The common forms of sigma bonds, according to this description, are $s+s,p_z+p_z,s+p_{z}and{d}_{z^2}+d_{z^2}$ (where z is defined as the axis of the bond or the internuclear axis).
Quantum theory also suggests that identical symmetry molecular orbitals (MO) mingle or hybridise. The wave functions $s+s,p_z+p_z$ molecular orbitals get merged as a result of this mixing of diatomic molecules. The extent of this blending (or hybridization) is determined by the relative energies of MOs with similar symmetry.
Overlapping of S-S orbital
One ‘s' orbital from each participating atom experiences head-on overlapping along the internuclear axis in this type of overlapping. Before one s orbital may overlap with another, it must be half-filled.

image taken from vedantu only, so no plagiarism may arise
Above is an illustration of two s orbitals overlapping to form a sigma bond. In $H_2$ molecules, where each hydrogen atom has a half-filled s orbital, this form of overlap occurs.

Note :
Head-on overlapping of atomic orbitals produces sigma bonds. The idea of sigma bonding is expanded to include bonding interactions when a single lobe of one orbital overlaps with a single lobe of another. Propane, for example, is made up of ten sigma bonds, one for each of the two CC bonds and one for each of the eight CH bonds.