Chemistry

Sodium tellurite (Na2TeO3) Sodium tellurite Sodium tellurite, Na2TeO3, is an inorganic salt of tellurous acid containing the tellurite anion. It is used in chemistry and microbiology and must be handled as a toxic tellurium…

Soft water: definition, sources, effects and treatment Soft water Soft water contains low concentrations of calcium and magnesium ions (often measured as CaCO3). This article explains its properties, natural origins, practical effects and common…

Sol (colloid) A sol is a colloidal suspension of tiny solid particles dispersed in a liquid. This article explains definition, properties, stability, common examples, industrial uses, and how so…

Solder — low‑melting metal alloy used to join materials Solder Overview of solder: types (soft and hard), common alloy compositions, flux and wetting, applications in electronics and plumbing, working methods, health and environmental consider…

Solid (state of matter) Solid A solid is a state of matter with particles held in fixed positions, giving definite shape and volume. This article explains structure, types, phase changes, examples and why solid…

Solid-state chemistry — synthesis, structure, and properties of solids Solid-state chemistry Study of the synthesis, structure, phases and properties of non-molecular solids; links to crystallography, mineralogy, thermodynamics and applications in electronics and materials…

Solubility: how substances dissolve and mix in liquids Solubility Solubility describes how much of a solute can dissolve in a solvent under given conditions. Covers definitions, types (miscible, saturated, supersaturated), factors, measures, exam…

Solution (chemistry): definition, types, properties and applications Solution (chemistry) A solution is a homogeneous mixture of two or more substances. This article explains composition, classification, solubility factors, concentration measures, colligative effects, a…

Solvation: interactions between solvents and solutes Solvation Solvation is the process by which solvent molecules surround and interact with solute particles, stabilizing them and enabling dissolution. It underpins solubility, reaction rates,…

Solvay process Industrial method, developed in the 19th century, for producing sodium carbonate from salt, ammonia and carbon dioxide with recovery of ammonia and lime-based reagents.

Solvent: definition, types, properties, uses and safety Solvent An accessible overview of solvents: what they are, main types (water, organic, inorganic), key properties, common applications, principles of solubility, selection and safety consi…

Solvent extraction (liquid–liquid extraction): principles, history and uses Solvent extraction Solvent extraction is a separation method that transfers solutes between two immiscible liquids. This article explains its principles, equipment, history, and common industrial and…

Sorption: adsorption and absorption — principles, types and applications Sorption Sorption is the umbrella term for uptake of one substance by another, either into a phase or at an interface. Covers mechanisms, measurement, environmental importance and common in…

Specific gravity: the density of a substance relative to water Specific gravity Specific gravity (SG) is the dimensionless ratio of a substance's density to the density of water. This article explains definition, measurement methods, applications, and practica…

Specific heat (specific heat capacity) Specific heat Specific heat is the heat required to raise the temperature of a unit mass of a substance by one degree. It characterizes how materials store thermal energy and varies with tempera…

Spectrophotometer: Principles, Types, and Practical Uses Spectrophotometer An introduction to spectrophotometers covering how they work, main components and types, historical context, typical applications in science and industry, and key distinctions.

Spectroscopy: study of matter via interaction with electromagnetic radiation Spectroscopy Spectroscopy examines how matter absorbs, emits or scatters electromagnetic radiation to reveal composition, structure, temperature, motion and other physical properties across man…

Spontaneity (chemistry): Gibbs free energy and thermodynamic favorability Spontaneity (chemistry) Overview of chemical spontaneity, the Gibbs free energy relation ΔG = ΔH − TΔS, how enthalpy and entropy affect spontaneity, connection to equilibrium and kinetics, and illustrativ…

Staggered conformation (organic chemistry) Staggered conformation A staggered conformation is a low-energy arrangement of bonded atoms in single-bonded molecules where substituents on adjacent atoms are rotated to maximize separation (60° torsion…

Stain: causes, types, removal methods, and intentional uses Stain A stain is a spot or discoloration differing from surrounding material. This article explains causes, common types, removal strategies, engineered resistance, and intentional stain…

Stainless Steel: Properties, Types, History and Practical Uses Stainless steel An accessible overview of stainless steel: its composition, principal families, properties and limits, brief history, common applications, and how grades and finishes affect perfor…

Standard state (chemical reference conditions) Standard state Definition and conventions for the chemical standard state: typical reference temperature and pressure, notation, uses in thermochemistry, and distinctions from STP and standard co…

Starch: plant carbohydrate, structure, uses, and culinary importance Starch Starch is a plant-produced polysaccharide of glucose units that stores energy. This article explains its structure, sources, digestion, culinary behavior, industrial uses and disti…

States of Matter: solids, liquids, gases, plasma and beyond States of matter Survey of the principal states (phases) of matter, their properties, common transitions, historical development, and practical significance.

Steam: properties, types, history, uses and safety Steam Steam is gaseous water formed by boiling or evaporation. This article explains its physical properties, varieties (saturated, superheated), historical role, common uses and safety…

Stereochemistry: three-dimensional arrangement of atoms and its chemical significance Stereochemistry Stereochemistry examines how the spatial arrangement of atoms in molecules determines isomerism, reactivity, physical and biological properties, covering chirality, conformations,…

Steric effects in chemistry Steric effects How the physical size and spatial crowding of atoms and groups affect molecular shape, reactivity, selectivity and the design of reagents, ligands and catalysts.

Sterling silver: composition, properties, history, and use Sterling silver Sterling silver is an alloy of 92.5% silver and 7.5% other metals, prized for its appearance and workability. This article covers composition, variants, history, hallmarking, care,…

Stibine (SbH3): properties, preparation, uses and safety Stibine Stibine (SbH3) is the simplest antimony hydride, a volatile covalent pnictogen hydride. It is chemically unstable, highly toxic, and found mainly in laboratory work and limited ind…

Stickiness: properties, causes, history and uses of sticky materials Sticky Stickiness denotes the tendency of surfaces or substances to adhere. Covers physical and chemical causes, types of adhesives, biological examples, testing methods, historical devel…

Still (distillation apparatus) Still A still is a device that separates or purifies liquids by boiling and condensation. Used in laboratories, industry and spirits production, stills vary from simple pot designs to co…

Stink bomb (novelty malodor device) Stink bomb A stink bomb is a small novelty device that releases an extremely unpleasant odor when activated. This article explains composition, use, safety, history, and regulatory concerns.

Stoichiometry: Quantitative Principles of Chemical Reactions Stoichiometry Stoichiometry is the quantitative study of reactants and products in chemical reactions, using mole ratios, conservation laws, limiting reagents and yield to predict amounts and gu…

Strong acid A strong acid is an aqueous proton donor that ionizes essentially completely in water. This article explains definition, properties, common examples, measurement, uses, hazards, an…

Strontium: properties, occurrence, uses and safety Strontium Overview of strontium (Sr, atomic number 38): physical and chemical properties, occurrence and production, common uses (pyrotechnics, glass, electronics), isotopes, biological role…

Strontium-90 (radioisotope) Strontium-90 Strontium-90 is a radioactive fission product and beta emitter with a ~28.8-year half-life. It is used in scientific, industrial and some medical applications and is a bone-seeking…

Structural isomer (constitutional isomer) Structural isomer A structural isomer is one of two or more compounds with the same molecular formula but different atom-to-atom connectivity; types include skeletal, positional (regio-), and functi…

Strychnine: properties, toxicity, history and uses Strychnine Strychnine is a potent plant-derived alkaloid known for its toxicity, historical uses as a pesticide and stimulant, and importance in medicine and forensic toxicology.

Styrene: structure, production, uses, and safety Styrene Styrene (C8H8) is an aromatic vinyl compound used to produce polystyrene and many copolymers; this article summarizes its chemistry, manufacture, applications, and health and envir…

Sublimation: the direct transition from solid to gas Sublimation Sublimation is the phase change in which a solid becomes a gas without passing through a liquid state. This article explains its causes, examples, uses, and practical distinctions.

Substance: material, composition, properties and classification Substance An overview of substance as material: scientific definitions, pure substances versus mixtures, properties, historical development and common examples like iron, water and air.

Substituent (chemistry) Substituent A substituent is an atom or group that replaces another atom in a molecule. This article explains types, nomenclature, effects on reactivity and properties, and distinctions from r…

Substitution reaction (chemistry) Substitution reaction A substitution reaction is one in which an atom or group in a molecule is replaced by a different atom or group. This article explains types, mechanisms, factors, common examples a…

Substrate (biochemistry) A substrate is the molecule upon which an enzyme acts. This article explains definitions, how substrates interact with enzyme active sites, reaction mechanisms, examples, kinetics…

Substrate (chemistry) A substrate in chemistry is the species or surface that undergoes a chemical process. The term covers reactants in solution, enzyme targets in biochemistry, and solid supports in s…

Sucralose: properties, uses, history and safety Sucralose Sucralose is a non-caloric artificial sweetener derived from sucrose. It is intensely sweet, heat- and pH-stable, widely used in foods and beverages, and subject to regulatory revi…

Sucrose (table sugar): structure, sources, uses, and health Sucrose Sucrose, commonly called table sugar or saccharose, is a plant-derived disaccharide of glucose and fructose used as a sweetener, preservative, and energy source; it has distinctive…

Sugar: types, chemistry, production, uses and health Sugar Concise overview of sugar as sweet-tasting carbohydrates: common types (sucrose, fructose, lactose), chemical nature, production sources, culinary and industrial uses, nutrition an…