Which of the molecules represented below contains carbon with sp2 hybridization? — Bonding Chemistry Question

STEPS:

1. Understand the relationship between hybridization and bonding patterns: Carbon atoms form hybrid orbitals based on their steric number (the number of bonded atoms plus lone pairs surrounding the carbon):
* $sp^3$ hybridization corresponds to a steric number of 4 (tetrahedral local geometry), which occurs when a carbon atom forms 4 single $\sigma$ bonds.
* $sp^2$ hybridization corresponds to a steric number of 3 (trigonal planar local geometry), which occurs when a carbon atom forms 3 $\sigma$ bonds (typically 2 single bonds and 1 double bond).
* $sp$ hybridization corresponds to a steric number of 2 (linear local geometry), which occurs when a carbon atom forms 2 $\sigma$ bonds (typically 1 single bond and 1 triple bond, or 2 double bonds).
2. Determine the Lewis structure and bonding of $\text{C}_2\text{H}_2\text{Cl}_2$ (dichloroethene): To satisfy the octet rule for both carbon atoms with this molecular formula, the two carbon atoms must be joined by a double bond ($\text{C}=\text{C}$). Each carbon is also single-bonded to one hydrogen atom ($\text{C}-\text{H}$) and one chlorine atom ($\text{C}-\text{Cl}$).
3. Calculate the steric number for the carbons in $\text{C}_2\text{H}_2\text{Cl}_2$: Each carbon atom is surrounded by 3 bonding domains (the $\text{C}=\text{C}$ double bond counts as one domain, alongside the two single bonds) and has 0 lone pairs.
4. Identify the hybridization: A steric number of 3 requires three hybrid orbitals, which are formed by mixing one s orbital and two p orbitals. This results in $sp^2$ hybridization for both carbon atoms, making Option D the correct answer.

*

WHY_OTHERS_WRONG:

• A is incorrect: In methane ($\text{CH}_4$), the central carbon atom is bonded to 4 hydrogen atoms via single covalent bonds. With a steric number of 4, the carbon atom is $sp^3$ hybridized.
• B is incorrect: In dichloromethane ($\text{CH}_2\text{Cl}_2$), the central carbon atom forms 4 single covalent bonds (2 with hydrogen and 2 with chlorine). This gives it a steric number of 4, resulting in $sp^3$ hybridization.
• C is incorrect: In ethane ($\text{C}_2\text{H}_6$), each carbon atom is bonded to 3 hydrogen atoms and single-bonded to the other carbon atom ($\text{H}_3\text{C}-\text{CH}_3$). Both carbons have a steric number of 4 and are $sp^3$ hybridized.
• E is incorrect: In dichloroethane ($\text{C}_2\text{H}_4\text{Cl}_2$), the carbon atoms are connected to each other by a single covalent bond ($\text{C}-\text{C}$). Each carbon also forms single bonds with 2 hydrogen atoms and 1 chlorine atom, giving both carbons a steric number of 4 and making them $sp^3$ hybridized.