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Chemical Bonding & Molecular Structure

Octahedral Geometry

A shape with six bonded atoms at the vertices of a regular octahedron, all bond angles being 90° or 180°.

AX₆ degrees
Inorganic & Coordination Chemistry

Octahedral Splitting

The division of the five d orbitals into a lower t₂g set of three and an upper e_g set of two under an octahedral ligand field.

t₂g (−0.4Δ₀), e_g (+0.6Δ₀) cm⁻¹
Chemical Bonding & Molecular Structure

Octet Rule

The observation that atoms tend to gain, lose or share electrons until they are surrounded by eight valence electrons.

Dimensionless
Chemical Bonding & Molecular Structure

Odd-Electron Molecule

A species containing an unpaired electron, so that its total electron count is odd and no octet structure is possible.

Dimensionless
Thermochemistry & Thermodynamics

Open System

A system that can exchange both energy and matter with its surroundings.

Dimensionless
Organic Chemistry

Optical Activity

The ability of a substance to rotate the plane of polarised light passing through it.

[α] = α / (l × c) degrees
Organic Chemistry

Optical Isomerism

Stereoisomerism in which molecules are non-superimposable mirror images and rotate plane-polarised light in opposite directions.

degrees
Inorganic & Coordination Chemistry

Optical Isomerism in Complexes

The existence of non-superimposable mirror-image forms of a coordination compound.

Δ and Λ degrees
Chemical Equilibrium

Optimum Conditions for Industrial Yield

The compromise set of temperature, pressure and catalyst chosen to balance equilibrium yield against reaction rate and cost.

Various
Chemical Kinetics & Catalysis

Order of Reaction

The power to which the concentration of a given reactant is raised in the experimentally determined rate law.

rate ∝ [A]^m Dimensionless
Inorganic & Coordination Chemistry

Ore

A naturally occurring mineral deposit from which a metal can be extracted profitably.

Dimensionless
Organic Chemistry

Organic Chemistry

The study of the structure, properties, composition and reactions of carbon-containing compounds.

Dimensionless
Inorganic & Coordination Chemistry

Organometallic Compound

A compound containing at least one direct bond between a metal and a carbon atom.

M–C Dimensionless
Solutions & Colligative Properties

Osmosis

The net movement of solvent molecules through a semipermeable membrane from a dilute to a concentrated solution.

Dimensionless
Solutions & Colligative Properties

Osmotic Pressure

The external pressure that must be applied to a solution to prevent the inward flow of solvent through a semipermeable membrane.

π = i M R T atm
Acids, Bases & Salts

Ostwald's Dilution Law

The relation showing how the degree of ionisation of a weak electrolyte increases on dilution.

Ka = cα² / (1 − α) mol/L
Analytical Chemistry & Spectroscopy

Outlier Test

A statistical procedure for deciding whether a suspect result differs enough from the others to be rejected.

Q = |suspect − nearest| / range Dimensionless
Chemical Equilibrium

Overall Formation Constant

The equilibrium constant for the formation of a complex directly from the free metal ion and all its ligands.

β_n = K₁K₂ … K_n Various
Chemical Kinetics & Catalysis

Overall Order

The sum of the individual orders with respect to every reactant appearing in the rate law.

n = m₁ + m₂ + … Dimensionless
Electrochemistry & Redox

Overpotential

The extra voltage beyond the theoretical value that must be applied before an electrode reaction proceeds at a useful rate.

η = E_applied − E_equilibrium V
Electrochemistry & Redox

Oxidation

The loss of electrons by a species, accompanied by an increase in its oxidation number.

M → Mⁿ⁺ + n e⁻ Dimensionless
Electrochemistry & Redox

Oxidation Number

The hypothetical charge an atom would carry if all its bonds were treated as fully ionic.

Σ oxidation numbers = overall charge Dimensionless
Stoichiometry & Chemical Reactions

Oxidation Number Method

A technique for balancing redox equations by equating the total increase and decrease in oxidation numbers.

Σ increase = Σ decrease Dimensionless
Organic Chemistry

Oxidation of Alcohols

The conversion of alcohols to carbonyl compounds or carboxylic acids by removal of hydrogen.

R–CH₂OH → RCHO → RCOOH Dimensionless