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A–Z
All A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Chemical Kinetics & Catalysis

Transition State

The highest-energy configuration along the reaction coordinate, at which bonds are partly broken and partly formed.

denoted ‡ kJ/mol
Chemical Kinetics & Catalysis

Transition State Theory

The theory that treats the activated complex as being in quasi-equilibrium with reactants and calculates rate from its decomposition…

k = (k_BT/h) e^(−ΔG‡/RT) Various
Nuclear & Radiochemistry

Transmutation

The conversion of one element into another through a change in the number of protons in the nucleus.

¹⁴N + ⁴He → ¹⁷O + ¹H Dimensionless
Electrochemistry & Redox

Transport Number

The fraction of the total current carried by a particular ion in an electrolyte solution.

t₊ = λ₊ / (λ₊ + λ₋) Dimensionless
Nuclear & Radiochemistry

Transuranium Elements

The synthetic elements with atomic numbers greater than 92, beyond uranium in the periodic table.

Z > 92 Dimensionless
Biochemistry & Polymer Chemistry

Triglyceride

An ester formed from glycerol and three fatty acid molecules, the main constituent of fats and oils.

glycerol + 3 RCOOH Dimensionless
Chemical Bonding & Molecular Structure

Trigonal Bipyramidal Geometry

A shape with five bonded atoms occupying three equatorial and two axial positions around a central atom.

AX₅ degrees
Chemical Bonding & Molecular Structure

Trigonal Planar Geometry

A flat molecular shape with three bonded atoms arranged around a central atom at 120°.

AX₃ degrees
States of Matter & Gas Laws

Triple Point

The unique temperature and pressure at which the solid, liquid and vapour phases of a substance coexist in equilibrium.

K, Pa
Thermochemistry & Thermodynamics

Trouton's Rule

The empirical observation that the entropy of vaporisation of many liquids is close to 88 J/(mol·K) at their boiling point.

ΔS_vap = ΔH_vap / T_b ≈ 88 J/(mol·K)
Chemical Kinetics & Catalysis

Turnover Number

The number of substrate molecules converted per catalytic site per unit time.

TON = molecules converted / active sites s⁻¹
Solutions & Colligative Properties

Tyndall Effect

The scattering of a light beam by colloidal particles, making the beam's path visible through the medium.

Dimensionless
Analytical Chemistry & Spectroscopy

Ultraviolet–Visible Spectroscopy

A technique that measures the absorption of ultraviolet and visible light by electronic transitions within molecules.

A = log(I₀/I) nm
Chemical Kinetics & Catalysis

Unimolecular Reaction

An elementary step in which a single molecule rearranges or decomposes.

A → products, rate = k[A] s⁻¹
States of Matter & Gas Laws

Unit Cell

The smallest repeating three-dimensional unit that, when stacked, reproduces the entire crystal lattice.

ρ = ZM / (a³N_A) pm
Chemical Equilibrium

Units of the Equilibrium Constant

The dimensions carried by an equilibrium constant, determined by the change in the number of moles in the balanced equation.

units = (mol/L)^Δn Various
Biochemistry & Polymer Chemistry

Unsaturated Fat

A fat containing one or more carbon–carbon double bonds in its fatty acid chains.

Dimensionless
Solutions & Colligative Properties

Unsaturated Solution

A solution containing less dissolved solute than it could hold at the given temperature.

mol/L
Nuclear & Radiochemistry

Uranium–Lead Dating

A radiometric method that determines the age of very old rocks from the ratio of uranium to its lead decay products.

²³⁸U → ²⁰⁶Pb (4.47 Ga) years
Chemical Bonding & Molecular Structure

Valence Bond Theory

The bonding model in which a covalent bond forms by the overlap of half-filled atomic orbitals on adjacent atoms.

Dimensionless
Inorganic & Coordination Chemistry

Valence Bond Theory of Complexes

The model describing coordinate bonding as the overlap of filled ligand orbitals with hybridised empty orbitals on the metal.

d²sp³, sp³d², sp³, dsp² Dimensionless
Atomic Structure & Periodicity

Valence Electron

An electron in the outermost occupied shell of an atom, available for bonding.

Dimensionless
Foundations of Chemistry

Valency

The combining capacity of an element, equal to the number of electrons an atom gains, loses or shares when forming compounds.

Dimensionless
Inorganic & Coordination Chemistry

Van Arkel Process

A purification method in which a metal is converted to a volatile iodide and then decomposed on a hot filament.

Ti + 2I₂ ⇌ TiI₄ °C