INORGANIC CHEMISTRY: BONDING THEORIES (VBT & MOT)

Vocabulary flashcards covering Valence Bond Theory, Molecular Orbital Theory, hybridization, magnetism, and symmetry concepts from the notes.

Valence Bond Theory (VBT)

A bonding theory describing molecules as localized bonds formed by overlap of atomic orbitals; includes sigma, pi, and delta bonds and explains valence via hybridization.

Sigma bond (σ)

A bond formed by head-on overlap of atomic orbitals along the internuclear axis; cylindrically symmetric about the bond.

Pi bond (π)

A bond formed by sideways overlap of p orbitals; electron density above and below the bond axis.

Delta bond (δ)

A bond formed by four-lobed sideways overlap (dx^2−y^2 or dxy); less common than σ and π bonds.

Hybridization

Mixing of atomic orbitals to form hybrid orbitals (sp, sp2, sp3, etc.) enabling multiple σ bonds and determining molecular geometry.

Hypervalent atoms

Atoms that expand the octet by accommodating more than eight electrons (expanded octet), common for period 3 and below.

sp mixing

Interaction of s and p orbitals to form hybrid orbitals; can give s-character to π MOs (notably in Li2 to N2).

Molecular Orbital Theory (MOT)

A theory in which atomic orbitals combine to form molecular orbitals that are delocalized over the entire molecule; MO energies follow Aufbau, Pauli, and Hund rules.

Molecular Orbital (MO)

A delocalized orbital spanning the molecule formed by linear combination of atomic orbitals (LCAO); MOs have definite energies.

Bonding Molecular Orbital (Bonding MO)

MO formed by constructive interference, lower in energy and increases electron density between nuclei.

Antibonding Molecular Orbital (Antibonding MO)

MO formed by destructive interference, higher in energy and decreases bond stability.

LCAO (Linear Combination of Atomic Orbitals)

Method of forming molecular orbitals by combining atomic orbitals from atoms in a molecule.

HOMO

Highest Occupied Molecular Orbital—the highest-energy MO that contains electrons.

LUMO

Lowest Unoccupied Molecular Orbital—the lowest-energy MO that does not contain electrons.

MOT bonding types

Bonding in MOT arises from overlap of AOs to form MOs (bonding or antibonding) with specific symmetry.

Homonuclear diatomic molecules

Diatomic molecules composed of the same element (e.g., H2, O2, F2); MO diagrams can involve s–p mixing (Li2 to N2).

Heteronuclear diatomic molecules

Diatomic molecules composed of different elements; bonding electrons are drawn toward the more electronegative atom, producing polar bonds.

Gerade vs Ungerade (g/u)

In MOT, MOs are labeled by inversion symmetry: gerade (g) is symmetric, ungerade (u) is antisymmetric with respect to inversion.

σg, σu, πg, πu

MO symmetry labels indicating bonding/antibonding character and inversion symmetry (g = gerade, u = ungerade).

Magnetic Properties

Property determined by electron spins in MOs; paramagnetic substances have unpaired electrons; diamagnetic substances have all electrons paired.

Paramagnetic

Molecules or ions with unpaired electrons; attracted to magnetic fields.

Diamagnetic

Molecules or ions with all electrons paired; weakly repelled by magnetic fields.

Hund's Rule

Electrons fill degenerate orbitals singly with parallel spins before pairing occurs.

Aufbau Principle

Electrons fill molecular orbitals from lowest to highest energy.

Pauli Exclusion Principle

No two electrons can have identical quantum numbers; an orbital holds up to two electrons with opposite spins.

Symmetry operations

Operations that map a molecule onto itself (E, Cn, σ, i, Sn) used to categorize point groups.

Principal axis

The symmetry axis with the highest n around which rotation leaves the molecule unchanged.

Point Group

The complete set of symmetry operations that describe a molecule’s overall symmetry.

Symmetry elements

Elements associated with symmetry operations (E, Cn, σ, i, Sn, Oh, etc.) used in classifying molecules.

Molecular geometry & point groups

Relationship between molecular shape (e.g., bent, trigonal, tetrahedral) and its point group (e.g., C2v, D3h).