Chemical Bonding & Molecular Structure — 60 Terms Defined

Antibonding Molecular Orbital Chemical Bonding & Molecular Structure Dimensionless A molecular orbital higher in energy than its parent atomic orbitals, whose occupation destabilises the molecule. ψ* = ψ_A − ψ_B

Back Bonding Chemical Bonding & Molecular Structure kJ/mol The donation of electron density from a filled orbital on one atom into an empty orbital on its bonded partner, in the direction opposite to the sigma bond. M(dπ) → L(π*)

Bent Geometry Chemical Bonding & Molecular Structure degrees 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

Bond Angle Chemical Bonding & Molecular Structure degrees The angle between two bonds that share a common atom.

Bond Energy Chemical Bonding & Molecular Structure kJ/mol The energy required to break one mole of a given bond homolytically in the gaseous state. A–B(g) → A(g) + B(g)

Bond Length Chemical Bonding & Molecular Structure pm The equilibrium distance between the nuclei of two bonded atoms. d ≈ r₁ + r₂

Bond Order Chemical Bonding & Molecular Structure Dimensionless The number of chemical bonds between a pair of atoms, or in molecular orbital terms half the difference between bonding and antibonding electrons. BO = (N_b − N_a) / 2

Bond Polarity Chemical Bonding & Molecular Structure Dimensionless The degree of unequal electron sharing in a covalent bond, arising from an electronegativity difference between the bonded atoms. Δχ = |χ_A − χ_B|

Bonding Molecular Orbital Chemical Bonding & Molecular Structure Dimensionless A molecular orbital lower in energy than the atomic orbitals from which it forms, whose occupation stabilises the molecule. ψ = ψ_A + ψ_B

Bonding Pair Chemical Bonding & Molecular Structure Dimensionless A pair of electrons shared between two atoms and responsible for holding them together.

Born–Haber Cycle Chemical Bonding & Molecular Structure kJ/mol 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

Chemical Bond Chemical Bonding & Molecular Structure kJ/mol The attractive force that holds atoms or ions together in a stable chemical species.

Coordinate Bond Chemical Bonding & Molecular Structure kJ/mol A covalent bond in which both shared electrons are supplied by the same atom. A: + B → A→B

Coordination Number Chemical Bonding & Molecular Structure Dimensionless The number of nearest neighbours immediately surrounding a given atom or ion in a lattice or complex.

Covalent Bond Chemical Bonding & Molecular Structure kJ/mol A bond formed when two atoms share one or more pairs of electrons so that both achieve a stable configuration. A· + ·B → A:B

Crystal Lattice Chemical Bonding & Molecular Structure Dimensionless The regular, repeating three-dimensional arrangement of particles in a crystalline solid.

Delocalisation Chemical Bonding & Molecular Structure Dimensionless The spreading of electrons over three or more atoms rather than their confinement between two.

Dipole Moment Chemical Bonding & Molecular Structure D The vector measure of the separation of positive and negative charge in a bond or molecule. μ = q × d

Dipole–Dipole Interaction Chemical Bonding & Molecular Structure kJ/mol The electrostatic attraction between the positive end of one polar molecule and the negative end of another. E ∝ μ₁μ₂ / r³

Electron Domain Geometry Chemical Bonding & Molecular Structure degrees The spatial arrangement of all electron domains — bonding and lone pairs alike — around a central atom.

Electron Sea Model Chemical Bonding & Molecular Structure Dimensionless The model of metallic bonding in which fixed cations are immersed in a mobile cloud of delocalised valence electrons.

Expanded Octet Chemical Bonding & Molecular Structure Dimensionless A bonding arrangement in which a central atom is surrounded by more than eight valence electrons.

Fajans' Rules Chemical Bonding & Molecular Structure Dimensionless A set of guidelines predicting how much covalent character an ionic bond will have.

Formal Charge Chemical Bonding & Molecular Structure Dimensionless The hypothetical charge on an atom in a Lewis structure assuming all bonding electrons are shared equally. FC = V − L − B/2