Use the localized electron model to describe the bonding in \(\mathrm{C}_{2} \mathrm{H}_{2}\) (exists as \(\mathrm{HCCH}\) ).

First, we need to calculate the total number of valence electrons in the HCCH molecule. Carbon (C) has 4 valence electrons and Hydrogen (H) has 1 valence electron. So for C2H2, the total number of valence electrons is: (2 Carbon atoms × 4 valence electrons) + (2 Hydrogen atoms × 1 valence electron) = 8 + 2 = 10 valence electrons.

In this molecule, the two central atoms are the Carbon atoms. They will form a bond with each other and Hydrogen atoms.

In the HCCH molecule, a Carbon atom forms a single bond with a Hydrogen atom, and the two Carbon atoms are bonded to each other. To satisfy the octet rule, the two Carbon atoms need to form a triple bond with each other. Thus, there are a total of 3 bonds in the molecule: 1. C-H (single bond) 2. C-C (triple bond)

Next, we need to determine the type of hybridization in the Carbon atoms: When Carbon forms a triple bond with another Carbon atom, it undergoes sp hybridization. Therefore, both Carbon atoms in HCCH are sp hybridized.

Now we can describe the bonding in the HCCH molecule using the localized electron model: 1. The two Carbon atoms are sp hybridized. 2. Each Carbon atom forms a sigma (σ) bond with the Hydrogen atom using one of their two sp hybrid orbitals. 3. The two Carbon atoms form a sigma (σ) bond with each other using their remaining sp hybrid orbitals. 4. The two Carbon atoms also form two pi (π) bonds with each other, using their unhybridized 2p orbitals. So, the bonding description in the HCCH molecule can be summarized as follows: - Two σ C-H bonds formed by the sp hybrid orbitals of Carbon and atomic orbitals of Hydrogen. - One σ C-C bond, formed by the sp hybrid orbitals of both Carbon atoms. - Two π C-C bonds, formed by the unhybridized 2p orbitals of both Carbon atoms.