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Chemical Bonding & Molecular Structure

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Chemical Bonding & Molecular Structure

Antibonding Molecular Orbital

A molecular orbital higher in energy than its parent atomic orbitals, whose occupation destabilises the molecule.

ψ* = ψ_A − ψ_B Dimensionless Chemical Bonding & Molecular Structure

Back Bonding

The donation of electron density from a filled orbital on one atom into an empty orbital on its bonded partner, in the direction opposite…

M(dπ) → L(π*) kJ/mol Chemical Bonding & Molecular Structure

Bent Geometry

A molecular shape in which two bonded atoms form an angle at a central atom that also carries one or more lone pairs.

AX₂E or AX₂E₂ degrees Chemical Bonding & Molecular Structure

Bond Angle

The angle between two bonds that share a common atom.

degrees Chemical Bonding & Molecular Structure

Bond Energy

The energy required to break one mole of a given bond homolytically in the gaseous state.

A–B(g) → A(g) + B(g) kJ/mol Chemical Bonding & Molecular Structure

Bond Length

The equilibrium distance between the nuclei of two bonded atoms.

d ≈ r₁ + r₂ pm Chemical Bonding & Molecular Structure

Bond Order

The number of chemical bonds between a pair of atoms, or in molecular orbital terms half the difference between bonding and antibonding…

BO = (N_b − N_a) / 2 Dimensionless Chemical Bonding & Molecular Structure

Bond Polarity

The degree of unequal electron sharing in a covalent bond, arising from an electronegativity difference between the bonded atoms.

Δχ = |χ_A − χ_B| Dimensionless Chemical Bonding & Molecular Structure

Bonding Molecular Orbital

A molecular orbital lower in energy than the atomic orbitals from which it forms, whose occupation stabilises the molecule.

ψ = ψ_A + ψ_B Dimensionless Chemical Bonding & Molecular Structure

Bonding Pair

A pair of electrons shared between two atoms and responsible for holding them together.

Dimensionless Chemical Bonding & Molecular Structure

Born–Haber Cycle

A thermochemical cycle applying Hess's law to determine the lattice energy of an ionic compound indirectly.

ΔH_f = ΔH_sub + IE + ½D + EA + U kJ/mol Chemical Bonding & Molecular Structure

Chemical Bond

The attractive force that holds atoms or ions together in a stable chemical species.

kJ/mol Chemical Bonding & Molecular Structure

Coordinate Bond

A covalent bond in which both shared electrons are supplied by the same atom.

A: + B → A→B kJ/mol Chemical Bonding & Molecular Structure

Coordination Number

The number of nearest neighbours immediately surrounding a given atom or ion in a lattice or complex.

Dimensionless Chemical Bonding & Molecular Structure

Covalent Bond

A bond formed when two atoms share one or more pairs of electrons so that both achieve a stable configuration.

A· + ·B → A:B kJ/mol Chemical Bonding & Molecular Structure

Crystal Lattice

The regular, repeating three-dimensional arrangement of particles in a crystalline solid.

Dimensionless Chemical Bonding & Molecular Structure

Delocalisation

The spreading of electrons over three or more atoms rather than their confinement between two.

Dimensionless Chemical Bonding & Molecular Structure

Dipole Moment

The vector measure of the separation of positive and negative charge in a bond or molecule.

μ = q × d D Chemical Bonding & Molecular Structure

Dipole–Dipole Interaction

The electrostatic attraction between the positive end of one polar molecule and the negative end of another.

E ∝ μ₁μ₂ / r³ kJ/mol Chemical Bonding & Molecular Structure

Electron Domain Geometry

The spatial arrangement of all electron domains — bonding and lone pairs alike — around a central atom.

degrees Chemical Bonding & Molecular Structure

Electron Sea Model

The model of metallic bonding in which fixed cations are immersed in a mobile cloud of delocalised valence electrons.

Dimensionless Chemical Bonding & Molecular Structure

Expanded Octet

A bonding arrangement in which a central atom is surrounded by more than eight valence electrons.

Dimensionless Chemical Bonding & Molecular Structure

Fajans' Rules

A set of guidelines predicting how much covalent character an ionic bond will have.

Dimensionless Chemical Bonding & Molecular Structure

Formal Charge

The hypothetical charge on an atom in a Lewis structure assuming all bonding electrons are shared equally.

FC = V − L − B/2 Dimensionless