Question

The electron pair in the \(\pi\)-bond of an alkene have: A. \(33 \%\) character and are at a lower energy level than the electron pair in the \(\sigma\)-bond. B. \(50 \%\) p character and are at a higher energy level than the electron pair in the \(\sigma\)-bond. C. \(100 \%\) p character and are at a lower energy level than the electron pair in the \(\sigma\) bond. D. \(100 \% p\) character and are at a higher energy level than the electron pair in the \(\sigma\)-bond.

Short answer

D. \(100\text{ percent}\) p character and are at a higher energy level than the electron pair in the \(\sigma\)-bond.

Step-by-step solution

- Understanding \(\text{sp}^2\) Hybridization

Alkenes have carbon atoms that are \(\text{sp}^2\) hybridized. This means each carbon atom forms three \(\sigma\) bonds (one with another carbon and two with hydrogen atoms) and one \(\pi\) bond through the overlap of unhybridized p orbitals.

- \(\pi\)-bond Character

The \(\pi\) bond in alkenes consists of one pair of electrons in an unhybridized p orbital, which means it has \(100\text{ percent}\) p character.

- Energy Levels of \(\sigma\) and \(\pi\) Bonds

\(\sigma\) bonds are formed by the overlap of orbitals directly between the bonding atoms, which results in a stronger and more stable bond that is at a lower energy level compared to \(\pi\) bonds. The \(\pi\) bond, formed by the sideways overlap of p orbitals, is generally at a higher energy level.

- Answer Analysis

From the information above, the correct description of the electron pair in the \(\pi\)-bond of an alkene is that it has \(100\text{ percent}\) p character and is at a higher energy level than the electron pair in the \(\sigma\)-bond.

Key concepts

sp2 hybridization

In alkenes, the carbon atoms undergo \(\text{sp}^2\) hybridization. This type of hybridization involves the mixing of one s orbital with two p orbitals (p_x and p_y) to form three \(\text{sp}^2\) hybrid orbitals. Each of these three hybrid orbitals forms a \(\text{sigma} (σ)\) bond. In the case of ethene (ethylene), for example, each carbon forms two \(\text{sigma} (σ)\) bonds with hydrogen atoms and one \(\text{sigma} (σ)\) bond with another carbon atom. The remaining p orbital (the p_z orbital) that does not participate in hybridization is left to form a \(\text{pi} (π)\) bond.

pi bond

A \(\text{pi} (π)\) bond in alkenes results from the sideways overlap of unhybridized p orbitals on adjacent carbon atoms. This type of bond is characterized by its 100% p character, meaning that the electrons involved in the \(\text{pi} (π)\) bond occupy pure p orbitals. Due to this arrangement, the electron density of a \(\text{pi} (π)\) bond is found above and below the plane of the atoms involved. A \(\text{pi} (π)\) bond is generally weaker and less stable than a \(\text{sigma} (σ)\) bond, which means that it is at a higher energy level.

sigma bond

A \(\text{sigma} (σ)\) bond is a type of chemical bond formed by the direct overlap of orbitals between two bonding atoms. In alkenes, \(\text{sigma} (σ)\) bonds are created from the merging of \(\text{sp}^2\) hybrid orbitals. These bonds are characterized by their strong and stable nature, which is a result of the head-on overlap of the orbitals. Because of this direct overlap, \(\text{sigma} (σ)\) bonds have a lower energy level compared to \(\text{pi} (π)\) bonds, and they contribute significantly to the structural integrity of the molecule.