8.3 Multiple Bonds and 8.4 Molecular Orbital Theory

Vocabulary flashcards covering the concepts of multiple bonding, hybridization, and molecular orbital theory from the lecture notes.

$\sigma$ bond

A covalent bond where the bonding electron density is symmetric about the internuclear axis, allowing for easy rotation around the bond.

$\pi$ bond

A bond formed by the side-by-side overlap of unhybridized $p$ orbitals, with electron density lobes located above and below the internuclear axis.

Ethene ($C_2H_4$)

A molecule featuring $sp^2$ hybridized carbon atoms in a trigonal planar geometry, consisting of five $\sigma$ bonds and one $\pi$ bond.

Acetylene ($C_2H_2$)

A linear molecule where carbon atoms are $sp$ hybridized and bound by one $\sigma$ bond and two $\pi$ bonds, forming a triple bond.

Paramagnetism

A property of a substance attracted to a magnetic field, resulting from the presence of unpaired electrons, as seen in $O_2$.

Diamagnetism

A property of materials in which all electrons are paired, causing the substance to weakly repel a magnetic field.

Molecular orbital theory (MO theory)

A bonding model that describes electrons as delocalized over the entire molecule using combinations of atomic orbitals.

Linear combination of atomic orbitals (LCAO)

The mathematical process of combining atomic orbital wave functions to generate molecular orbitals.

Bonding orbital

A lower-energy molecular orbital in which electron density is concentrated between nuclei, creating a force that holds atoms together.

Antibonding orbital

A higher-energy molecular orbital, often marked with an asterisk ($\ast$), that contains a node between nuclei and pulls them apart.

Bond order

A measure of bond strength calculated using the formula: $\text{bond order} = \frac{(\text{number of bonding electrons} - \text{number of antibonding electrons})}{2}$.

s-p mixing

A phenomenon where $\sigma_s$ and $\sigma_p$ wave functions combine, shifting orbital energies so that $\sigma_s$ becomes more stable and $\sigma_p$ becomes less stable.

$sp$ Hybridization

The mixing of a valence $s$ orbital and one valence $p$ orbital to yield two equivalent hybrid orbitals oriented at $180^\circ$.

Benzene ($C_6H_6$)

A molecule in which each carbon is $sp^2$ hybridized and the $\pi$ bond electrons are delocalized throughout the ring.

Gouy balance

An experimental apparatus used to determine the number of unpaired electrons by measuring the mass change of a sample in a magnetic field.

Constructive interference

The interaction of in-phase waves that produce a wave with greater amplitude, leading to bonding molecular orbitals.

Destructive interference

The interaction of out-of-phase waves that produce a wave with less or no amplitude, resulting in a node in antibonding orbitals.

Homonuclear diatomic molecules

Molecules composed of two identical atoms, such as $Li_2$, $Be_2$, and $N_2$.