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Terms starting with E

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Atomic Structure & Periodicity

Electron Affinity

The energy change when one mole of gaseous atoms each gains an electron to form gaseous negative ions.

X(g) + e⁻ → X⁻(g) kJ/mol
Nuclear & Radiochemistry

Electron Capture

Radioactive decay in which a nucleus absorbs an inner-shell electron, converting a proton into a neutron.

p + e⁻ → n + ν MeV
Atomic Structure & Periodicity

Electron Configuration

The notation describing how an atom's electrons are distributed among its available orbitals.

1s² 2s² 2p⁶ … Dimensionless
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
Atomic Structure & Periodicity

Electronegativity

The relative tendency of an atom in a covalent bond to attract the shared pair of electrons towards itself.

ΔEN determines bond polarity Dimensionless
Organic Chemistry

Electrophile

An electron-deficient species that seeks and accepts a pair of electrons from an electron-rich centre.

E⁺ Dimensionless
Organic Chemistry

Electrophilic Addition

A reaction in which an electrophile adds across a carbon–carbon multiple bond, converting a pi bond into two sigma bonds.

C=C + E–Nu → C(E)–C(Nu) Dimensionless
Organic Chemistry

Electrophilic Substitution

A reaction in which an electrophile replaces a hydrogen atom on an aromatic ring.

ArH + E⁺ → ArE + H⁺ Dimensionless
Analytical Chemistry & Spectroscopy

Electrophoresis

A separation technique in which charged species migrate through a medium under an applied electric field.

v = μE cm/s
Electrochemistry & Redox

Electroplating

The deposition of a thin metal coating onto a conducting surface by electrolysis.

g
Electrochemistry & Redox

Electrorefining

The purification of a metal by dissolving it from an impure anode and depositing it in pure form at the cathode.

Dimensionless
Electrochemistry & Redox

Electrowinning

The extraction of a metal from a solution or molten salt of its ore by electrolysis.

kWh/kg
Foundations of Chemistry

Element

A pure substance composed entirely of atoms that share the same atomic number and therefore cannot be split into simpler substances by…

Dimensionless
Chemical Kinetics & Catalysis

Elementary Reaction

A reaction that occurs in a single step exactly as written, with no detectable intermediate.

order = molecularity Dimensionless
Stoichiometry & Chemical Reactions

Elimination Reaction

A reaction in which two substituents are removed from adjacent atoms, generating a multiple bond.

R–CH₂–CHX–R → R–CH=CH–R + HX Dimensionless
Inorganic & Coordination Chemistry

Ellingham Diagram

A plot of the standard free energy of formation of metal oxides against temperature, used to choose a reduction route.

ΔG° = ΔH° − TΔS° kJ/mol
Foundations of Chemistry

Empirical Formula

The chemical formula giving the simplest whole-number ratio of atoms of each element in a compound.

ratio = (mass % ÷ A_r), normalised Dimensionless
Solutions & Colligative Properties

Emulsion

A colloidal dispersion of one liquid as fine droplets throughout another liquid with which it is immiscible.

nm
Organic Chemistry

Enantiomer

One of a pair of stereoisomers that are non-superimposable mirror images of each other.

(+) and (−), or R and S degrees
Acids, Bases & Salts

End Point

The point in a titration at which the indicator changes colour, signalling that the reaction is judged complete.

mL
Thermochemistry & Thermodynamics

Endergonic Reaction

A reaction with a positive Gibbs free energy change, which requires an input of energy to proceed.

ΔG > 0 kJ/mol
Stoichiometry & Chemical Reactions

Endothermic Reaction

A reaction that absorbs energy from the surroundings, giving a positive enthalpy change.

ΔH > 0 kJ/mol
Chemical Kinetics & Catalysis

Energy Profile Diagram

A plot of potential energy against reaction coordinate showing reactants, transition states, intermediates and products.

kJ/mol