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Inorganic & Coordination Chemistry

Sandwich Compound

An organometallic compound in which a metal atom is held between two parallel planar cyclic ligands.

e.g. Fe(C₅H₅)₂ Dimensionless
Stoichiometry & Chemical Reactions

Saponification

The alkaline hydrolysis of an ester, particularly a triglyceride, to give a carboxylate salt and an alcohol.

RCOOR′ + NaOH → RCOONa + R′OH Dimensionless
Biochemistry & Polymer Chemistry

Saturated Fat

A fat whose fatty acid chains contain only single carbon–carbon bonds.

Dimensionless
Solutions & Colligative Properties

Saturated Solution

A solution in dynamic equilibrium with undissolved solute, containing the maximum amount that will dissolve at that temperature.

rate dissolve = rate crystallise mol/L
Organic Chemistry

Saturation and Unsaturation

The distinction between compounds containing only single bonds and those containing multiple bonds or rings.

DoU = (2C + 2 + N − H − X)/2 Dimensionless
States of Matter & Gas Laws

Schottky Defect

A point defect in which equal numbers of cations and anions are missing from their lattice sites.

Dimensionless
Atomic Structure & Periodicity

Schrödinger Wave Equation

The fundamental equation of quantum mechanics whose solutions give the allowed energies and wavefunctions of a system.

Ĥψ = Eψ J
Nuclear & Radiochemistry

Scintillation Counter

A detector in which radiation causes a material to emit flashes of light that are counted and measured.

counts/s
Thermochemistry & Thermodynamics

Second Law of Thermodynamics

The total entropy of the universe increases in every spontaneous process.

ΔS_universe > 0 J/K
Chemical Kinetics & Catalysis

Second-Order Reaction

A reaction whose rate depends on the square of one concentration or on the product of two concentrations.

1/[A] = 1/[A]₀ + kt L/(mol·s)
Electrochemistry & Redox

Secondary Cell

A cell whose reaction can be reversed by an applied current, allowing it to be recharged and reused.

V
Analytical Chemistry & Spectroscopy

Secondary Standard

A solution whose concentration has been established by titration against a primary standard.

mol/L
Biochemistry & Polymer Chemistry

Secondary Structure

Local regular folding patterns of a polypeptide backbone stabilised by hydrogen bonds.

Dimensionless
Inorganic & Coordination Chemistry

Secondary Valence

In Werner's theory, the non-ionisable valence corresponding to the coordination number, satisfied by ligands in fixed spatial positions.

Dimensionless
Nuclear & Radiochemistry

Secular Equilibrium

The steady state reached when a long-lived parent supports a short-lived daughter at constant activity.

λ₁N₁ = λ₂N₂ Bq
Electrochemistry & Redox

Selective Discharge

The preferential reaction of one ion over others at an electrode during electrolysis.

V
Chemical Equilibrium

Selective Precipitation

The separation of ions from a mixture by adding a reagent that precipitates them one at a time.

mol/L
Chemical Kinetics & Catalysis

Selectivity

The ability of a catalyst to direct a reaction towards one particular product among several possible ones.

selectivity = desired product / total product Dimensionless
Acids, Bases & Salts

Self-Ionisation of Water

The reaction in which two water molecules transfer a proton to give a hydronium and a hydroxide ion.

2H₂O ⇌ H₃O⁺ + OH⁻ mol/L
Solutions & Colligative Properties

Semipermeable Membrane

A barrier that allows solvent molecules to pass while blocking larger solute particles.

Dimensionless
Analytical Chemistry & Spectroscopy

Sensitivity

The change in an instrument's response for a given change in analyte concentration.

S = dSignal / dConcentration Various
Atomic Structure & Periodicity

Shielding Effect

The reduction in the nuclear attraction felt by an outer electron caused by repulsion from electrons in inner shells.

Z_eff = Z − σ Dimensionless
Foundations of Chemistry

SI Base Units

The seven defined units of the International System from which every other measurement unit is derived.

Various
Nuclear & Radiochemistry

Sievert

The SI unit of equivalent dose, weighting absorbed dose by the biological damage the radiation type causes.

H = D × w_R Sv