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Electron Affinity Atomic Structure & Periodicity kJ/mol The energy change when one mole of gaseous atoms each gains an electron to form gaseous negative ions. X(g) + e⁻ → X⁻(g) Electron Capture Nuclear & Radiochemistry MeV Radioactive decay in which a nucleus absorbs an inner-shell electron, converting a proton into a neutron. p + e⁻ → n + ν Electron Configuration Atomic Structure & Periodicity Dimensionless The notation describing how an atom's electrons are distributed among its available orbitals. 1s² 2s² 2p⁶ … 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. Electronegativity Atomic Structure & Periodicity Dimensionless The relative tendency of an atom in a covalent bond to attract the shared pair of electrons towards itself. ΔEN determines bond polarity Electrophile Organic Chemistry Dimensionless An electron-deficient species that seeks and accepts a pair of electrons from an electron-rich centre. E⁺ Electrophilic Addition Organic Chemistry Dimensionless 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) Electrophilic Substitution Organic Chemistry Dimensionless A reaction in which an electrophile replaces a hydrogen atom on an aromatic ring. ArH + E⁺ → ArE + H⁺ Electrophoresis Analytical Chemistry & Spectroscopy cm/s A separation technique in which charged species migrate through a medium under an applied electric field. v = μE Electroplating Electrochemistry & Redox g The deposition of a thin metal coating onto a conducting surface by electrolysis. Electrorefining Electrochemistry & Redox Dimensionless The purification of a metal by dissolving it from an impure anode and depositing it in pure form at the cathode. Electrowinning Electrochemistry & Redox kWh/kg The extraction of a metal from a solution or molten salt of its ore by electrolysis. Element Foundations of Chemistry Dimensionless A pure substance composed entirely of atoms that share the same atomic number and therefore cannot be split into simpler substances by chemical means. Elementary Reaction Chemical Kinetics & Catalysis Dimensionless A reaction that occurs in a single step exactly as written, with no detectable intermediate. order = molecularity Elimination Reaction Stoichiometry & Chemical Reactions Dimensionless A reaction in which two substituents are removed from adjacent atoms, generating a multiple bond. R–CH₂–CHX–R → R–CH=CH–R + HX Ellingham Diagram Inorganic & Coordination Chemistry kJ/mol A plot of the standard free energy of formation of metal oxides against temperature, used to choose a reduction route. ΔG° = ΔH° − TΔS° Empirical Formula Foundations of Chemistry Dimensionless The chemical formula giving the simplest whole-number ratio of atoms of each element in a compound. ratio = (mass % ÷ A_r), normalised Emulsion Solutions & Colligative Properties nm A colloidal dispersion of one liquid as fine droplets throughout another liquid with which it is immiscible. Enantiomer Organic Chemistry degrees One of a pair of stereoisomers that are non-superimposable mirror images of each other. (+) and (−), or R and S End Point Acids, Bases & Salts mL The point in a titration at which the indicator changes colour, signalling that the reaction is judged complete. Endergonic Reaction Thermochemistry & Thermodynamics kJ/mol A reaction with a positive Gibbs free energy change, which requires an input of energy to proceed. ΔG > 0 Endothermic Reaction Stoichiometry & Chemical Reactions kJ/mol A reaction that absorbs energy from the surroundings, giving a positive enthalpy change. ΔH > 0 Energy Profile Diagram Chemical Kinetics & Catalysis kJ/mol A plot of potential energy against reaction coordinate showing reactants, transition states, intermediates and products.