Determine the electron geometry of C2H2 (skeletal structure HCCH).
(Hint: Determine the geometry around each of the two central atoms.)
A. trigonal planar
B. linear
C. pentahedral
D. hexahedral E. tetrahedral
The Correct Answer and Explanation is:
To determine the electron geometry of ethyne (C₂H₂), also known as acetylene, we need to analyze the bonding around each carbon atom in the skeletal structure HC≡CH. Ethyne consists of two carbon atoms triple-bonded to each other and each carbon atom is also bonded to a hydrogen atom.
Step 1: Identify the Central Atoms
In the skeletal structure, the two central atoms are the carbon atoms (C). Each carbon is involved in a triple bond with the other carbon, as well as a single bond with a hydrogen atom.
Step 2: Count Electron Domains
For each carbon atom:
- The triple bond between the two carbon atoms counts as one electron domain.
- The single bond to the hydrogen atom counts as one electron domain.
Thus, each carbon atom has a total of two electron domains (one from the triple bond and one from the bond to hydrogen).
Step 3: Determine the Electron Geometry
According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the electron geometry around a central atom is determined by the number of electron domains surrounding it. When there are two electron domains, the arrangement is described as linear. This means the atoms will orient themselves as far apart as possible to minimize repulsion.
Conclusion
Both carbon atoms in C₂H₂ exhibit the same electron geometry due to their similar bonding arrangements. Since each carbon has two electron domains and the most favorable arrangement for two domains is linear, the electron geometry of each carbon atom is linear.
Therefore, the correct answer for the electron geometry of C₂H₂ is B. linear. This linear arrangement contributes to the overall shape of the molecule, leading to bond angles of approximately 180 degrees between the hydrogen-carbon-hydrogen bonds, which is characteristic of linear molecules.