[VISUAL] 7. In the reaction represented above, what is the hybridization of the C atoms before and a — Bonding Chemistry Question

STEPS:

1. Understand how to determine the hybridization of an atom: In organic molecules, the hybridization of carbon can be quickly determined by its steric number (the number of shared bonding regions/directions plus the number of lone pairs surrounding the atom):
* A steric number of 2 (2 bonding directions) corresponds to $sp$ hybridization (linear geometry).
* A steric number of 3 (3 bonding directions) corresponds to $sp^2$ hybridization (trigonal planar geometry).
* A steric number of 4 (4 bonding directions) corresponds to $sp^3$ hybridization (tetrahedral geometry).
*(Note: Under VSEPR theory, double and triple bonds count as a single bonding region/direction).*
2. Analyze the carbon atoms BEFORE the reaction (in ethene, $\text{C}_2\text{H}_4$):
* Examine either of the carbon atoms in the reactant: it is bonded to three other atoms (two hydrogen atoms via single covalent bonds and one carbon atom via a double covalent bond).
* Carbon has four valence electrons and all are shared in bonds, meaning there are no lone pairs on the carbon atom.
* Steric number = 3 bonding regions + 0 lone pairs = 3.
* Therefore, the hybridization of both carbon atoms before the reaction is $sp^2$.
3. Analyze the carbon atoms AFTER the reaction (in the cyclic product):
* Examine either of the carbon atoms in the product: the carbon-carbon double bond has been broken and replaced by a carbon-carbon single bond.
* Each carbon atom is now bonded to four separate atoms: two hydrogen atoms (single bonds), one carbon atom (single bond), and one oxygen atom (single bond).
* There are still no lone pairs on the carbon atom.
* Steric number = 4 bonding regions + 0 lone pairs = 4.
* Therefore, the hybridization of both carbon atoms after the reaction is $sp^3$.
4. Select the matching option: The change in hybridization is Before: $sp^2$, After: $sp^3$, which corresponds to Option D.

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WHY_OTHERS_WRONG:

• Options A and B are incorrect: Both options state that the carbon atoms are initially $sp$ hybridized. Carbon atoms only exhibit $sp$ hybridization when they have a steric number of 2, such as in alkynes containing a triple bond (e.g., ethyne, $\text{C}_2\text{H}_2$) or cumulative double bonds (e.g., carbon dioxide, $\text{CO}_2$).
• Option C is incorrect: This option states that the carbon atoms become $sp$ hybridized after the reaction. The product carbon atoms are bonded to four different atoms with single bonds in a tetrahedral molecular geometry, which is characteristic of $sp^3$ hybridization rather than the linear $sp$ hybridization.