S Orbital
A spherically symmetric atomic orbital with angular momentum quantum number l = 0. Each energy level contains one s orbital. The 1s orbital is the lowest energy orbital in hydrogen…
Chemical Glossary — Letter S
131 chemicals found starting with "S"
Saccharate
Saccharate refers to a salt or ester of saccharic acid (glucaric acid, HOOC-(CHOH)₄-COOH), a dicarboxylic acid formed by the nitric acid oxidation of glucose. Saccharates are forme…
Saccharic
Saccharic is an adjective describing compounds derived from or related to saccharic acid (glucaric acid), a dicarboxylic acid obtained by the oxidation of sugars such as glucose. T…
Saccharic Acid
Saccharic acid (glucaric acid, HOOC-(CHOH)₄-COOH) is a six-carbon dicarboxylic acid formed by the oxidation of glucose or other hexoses with nitric acid. It is a white crystalline …
Saccharide
Saccharides are the chemical name for carbohydrates — compounds of carbon, hydrogen, and oxygen with the general empirical formula (CH₂O)n, including monosaccharides (simple sugars…
Safranine
Safranine (safranin) is a red cationic dye belonging to the phenazine class of aromatic heterocyclic compounds, widely used as a biological stain in histology, microbiology, and th…
Salicylaldehyde
Salicylaldehyde (2-hydroxybenzaldehyde, C₆H₄(OH)(CHO)) is an aromatic aldehyde with a hydroxyl group ortho to the aldehyde group on the benzene ring, occurring naturally in the ess…
Salicylate
Salicylates are the salts and esters of salicylic acid (2-hydroxybenzoic acid), the most notable being aspirin (acetylsalicylic acid), sodium salicylate, and methyl salicylate (oil…
Salinometer
A salinometer is an instrument used to measure the salinity (salt content) of a liquid, typically seawater or brine. It may operate on the principle of electrical conductivity (con…
Salt
An ionic compound formed by the reaction of an acid with a base, consisting of a cation from the base and an anion from the acid. Common table salt is sodium chloride (NaCl). Salts…
Salt Bridge
A salt bridge is a device (usually a U-shaped tube filled with an electrolyte solution such as KNO₃ or KCl in agar gel) used in electrochemical cells to maintain electrical neutral…
Salt Bridge
A device used in electrochemical cells to maintain electrical neutrality by allowing ion flow between two half-cells. It typically consists of a U-tube filled with a gel or saturat…
Salt Hydrolysis
Salt hydrolysis is the reaction of the cation or anion (or both) of a salt with water to produce an acidic or basic solution. When a salt of a weak acid and strong base dissolves, …
Samarium
Samarium is a moderately hard, silvery rare earth metal, atomic number 62. Used in SmCo permanent magnets (samarium cobalt), which retain magnetism at higher temperatures than NdFe…
Saponification
Saponification is the alkaline hydrolysis of an ester to produce a carboxylate salt (soap) and an alcohol. The reaction of triglycerides (fats or oils) with sodium or potassium hyd…
Saponification
The hydrolysis of an ester with a strong base to produce an alcohol and the salt of a carboxylic acid. The classic example is the reaction of fats (triglycerides) with sodium hydro…
Saturated Compound
An organic compound in which all carbon-carbon bonds are single bonds (no double or triple bonds). Saturated hydrocarbons (alkanes) cannot undergo addition reactions. The term also…
Saturated Hydrocarbons
Saturated hydrocarbons are organic compounds composed only of carbon and hydrogen atoms connected exclusively by single carbon-carbon bonds (no double or triple bonds), with each c…
Saturated Solution
A saturated solution is a solution that contains the maximum amount of solute that can dissolve at a given temperature and pressure. Any additional solute added to a saturated solu…
Saturated Solution
A solution containing the maximum amount of dissolved solute at a given temperature and pressure. No more solute can dissolve at equilibrium. Adding more solute creates a dynamic e…
Scandium
Scandium is a silvery-white transition metal, atomic number 21. Rare in nature despite being the 23rd most abundant element. First member of the transition metals (Period 4, Group …
Screening Effect
The screening effect (shielding effect) describes the reduction in the effective nuclear charge (Z_eff) experienced by an outer electron due to the repulsion from inner electrons. …
Seaborgium
Seaborgium is a synthetic radioactive transactinide element named after Glenn T. Seaborg. It is predicted to have properties similar to tungsten. First confirmed synthesis in 1974 …
Second Law of Thermodynamics
The second law of thermodynamics states that in any spontaneous process, the total entropy of the universe (system + surroundings) always increases. Equivalently, heat does not spo…
Second Law of Thermodynamics
The law stating that in any spontaneous process, the total entropy of the universe increases (ΔSuniv > 0). Equivalently, heat flows spontaneously from hot to cold, and it is imposs…
Secondary Standard
A secondary standard is a standard solution whose concentration has been determined by comparison (standardization) against a primary standard solution, rather than being prepared …
Secondary Voltaic Cells
Secondary voltaic cells (rechargeable batteries) are electrochemical cells that can be recharged by passing an electric current through them in the reverse direction, reversing the…
Selenium
Selenium is a non-metal/metalloid, atomic number 34. An essential trace element for humans and many other organisms (component of selenoproteins, glutathione peroxidase). Has both …
Semiconductor
A semiconductor is a material with electrical conductivity intermediate between that of a conductor and an insulator, characterized by a band gap of approximately 0.1–3 eV that all…
Semiconductors
Materials with electrical conductivity between conductors and insulators, which can be controlled by doping, temperature, or light. Silicon and germanium are the most important sem…
Semipermeable Membrane
A semipermeable membrane is a membrane that allows the passage of certain molecules or ions (typically the solvent) while blocking others (solute particles), based on size, charge,…
Separating Funnel
A piece of laboratory glassware with a stopcock used to separate two immiscible liquids of different densities or to perform liquid-liquid extraction. The denser liquid settles to …
Shell
An electron energy level or principal quantum shell, denoted by the principal quantum number n. Each shell contains one or more subshells (s, p, d, f). The first shell (n=1) holds …
Shielding Effect
The shielding effect (electron shielding or screening) refers to the reduction of the attractive force experienced by outer electrons due to the presence of inner-shell electrons b…
Sievert
The sievert (Sv) is the SI unit of effective radiation dose — the measure of the biological effect of ionizing radiation on human tissue. It accounts not only for the absorbed dose…
Sigma Bond
A covalent bond formed by the direct (head-on) overlap of atomic orbitals along the internuclear axis. All single bonds are sigma bonds. Sigma bonds can freely rotate about the bon…
Sigma Bonds
A sigma (σ) bond is the strongest type of covalent bond, formed by the direct (head-on) overlap of atomic orbitals along the internuclear axis, resulting in electron density concen…
Sigma Complex
An intermediate formed in electrophilic aromatic substitution reactions when the electrophile forms a covalent bond with one carbon of the aromatic ring, disrupting the aromatic pi…
Sigma Orbital
A sigma (σ) molecular orbital is formed by the linear combination of atomic orbitals with constructive overlap along the internuclear axis, producing a bonding orbital with electro…
Significant Figures
The number of meaningful digits in a measurement that reflect the precision of the measurement. Rules for significant figures ensure that calculated results do not show more precis…
Silicon
Silicon is a lustrous metalloid, atomic number 14, second most abundant element in Earth crust (28%). Pure silicon is a semiconductor - foundation of modern electronics. Forms SiO2…
Silicones
Silicones are synthetic polymers consisting of repeating –Si(R₂)–O– units (siloxane backbone), where R is typically an organic group such as methyl or phenyl, giving a hybrid inorg…
Silver
Silver is a lustrous, soft, white precious metal, atomic number 47. Has the highest electrical and thermal conductivity of all metals. Used since antiquity for jewellery, currency,…
Single Bond
A single bond is a covalent bond in which one pair of electrons is shared between two atoms. It is the most basic type of covalent bond, denoted by a single line between atoms in s…
Single Bond
A covalent bond formed by one shared pair of electrons (one sigma bond) between two atoms. Single bonds allow free rotation about the bond axis and are longer and weaker than doubl…
Slag
The by-product of smelting ores, consisting of waste material (mainly metal oxides and silicates) that separates from the refined metal. In the iron blast furnace, calcium silicate…
Smelting
Smelting is a pyrometallurgical process used to extract metals from their ores by heating the ore with a reducing agent (usually carbon/coke) and a flux at high temperatures in a f…
Soap
The sodium or potassium salt of a long-chain fatty acid, produced by saponification of fats or oils with a strong base. Soaps are surfactants with a hydrophilic carboxylate head an…
Sodium
Sodium is a soft, silvery-white alkali metal, atomic number 11. Highly reactive with water. Essential for life - regulates fluid balance and nerve impulses. Sixth most abundant ele…
Soft Acid
In HSAB theory, a Lewis acid that is large, has low positive charge or zero charge, and is highly polarizable. Soft acids prefer to bond with soft bases. Examples include Cu⁺, Ag⁺,…
Soft Base
In HSAB theory, a Lewis base that is large, highly polarizable, and of low electronegativity. Soft bases prefer to bond with soft acids. Examples include S²⁻, RS⁻, CO, CN⁻, and pho…
Solid
A state of matter characterized by definite shape and volume, with particles in fixed positions and close together. Solids are nearly incompressible and maintain their shape withou…
Solubility
The maximum amount of a solute that can dissolve in a given amount of solvent at a specified temperature. Expressed as g/100 mL or mol/L. Solubility depends on temperature (usually…
Solubility Product
The equilibrium constant (Ksp) for the dissolution of a slightly soluble ionic compound. Ksp = [cation]^m[anion]^n for MₘAₙ. A smaller Ksp indicates lower solubility. Used to predi…
Solubility Product Constant
The solubility product constant (Ksp) is the equilibrium constant for the dissolution of a sparingly soluble ionic compound in water, expressed as the product of the molar concentr…
Solubility Product Principle
The solubility product principle states that in a saturated solution of a sparingly soluble electrolyte, the ionic concentration product (ion product, Q) equals the solubility prod…
Solubility Rules
A set of generalizations about which ionic compounds are soluble in water. Most nitrates, group 1 salts, and ammonium salts are soluble. Most sulfates are soluble (except BaSO₄, Pb…
Solute
A solute is the substance that is dissolved in a solvent to form a solution. The solute is typically present in a smaller amount than the solvent. When sodium chloride (solute) is …
Solute
The substance dissolved in a solvent to form a solution. The solute is typically present in smaller amounts than the solvent. In a sugar-water solution, sugar is the solute. Solute…
Solution
A solution is a homogeneous mixture of two or more substances where the solute is uniformly distributed at the molecular or ionic level within the solvent. Solutions can involve al…
Solution
A homogeneous mixture of two or more substances. The solvent (usually the major component) dissolves the solute. Solutions can be solid (alloys), liquid (aqueous solutions), or gas…
Solvation
Solvation is the process by which solvent molecules surround and interact with solute molecules or ions when a substance dissolves. In aqueous solutions (hydration), water molecule…
Solvation
The process by which solvent molecules surround and stabilize dissolved solute ions or molecules. In aqueous solutions, solvation is called hydration. The enthalpy of solvation (ne…
Solvation Shell
The layer of solvent molecules surrounding a dissolved ion or molecule. In aqueous solutions, the innermost hydration shell of water molecules is strongly oriented by the charge or…
Solvent
A solvent is the substance, typically present in the greater amount, that dissolves a solute to form a solution. Water is called the 'universal solvent' because of its ability to d…
Solvent
The component of a solution present in the largest amount, in which the solute is dissolved. The solvent determines the physical state of the solution. Water is the universal solve…
Solvents
Substances capable of dissolving other substances to form solutions. Polar solvents (water, alcohols) dissolve ionic and polar compounds; nonpolar solvents (hexane, benzene) dissol…
Solvolysis
Solvolysis is a chemical reaction in which a molecule reacts with the solvent in which it is dissolved, with the solvent acting as a nucleophile or base. When the solvent is water,…
Specific Gravity
Specific gravity (SG) is the ratio of the density of a substance to the density of a reference substance (usually water at 4°C for liquids/solids, or air for gases). It is a dimens…
Specific Heat
Specific heat capacity (c) is the amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin) at constant pressure, mea…
Specific Heat Capacity
The amount of heat energy required to raise the temperature of 1 gram of a substance by 1°C (or 1 K). Expressed in J/g·°C. Water has a high specific heat (4.18 J/g·°C), which moder…
Specific Rate Constant
The specific rate constant (k) is the proportionality constant in the rate law expression for a chemical reaction (rate = k[A]ᵐ[B]ⁿ), with units that depend on the overall order of…
Spectator Ion
An ion present in a reaction mixture that does not participate in the actual chemical change. Spectator ions appear on both sides of the complete ionic equation and are canceled wh…
Spectator Ions
Spectator ions are ions present in a reaction mixture that do not participate in the actual chemical change; they appear on both sides of the complete ionic equation and cancel out…
Spectral Line
A spectral line is a dark or bright line in an otherwise uniform spectrum, resulting from absorption or emission of light at a specific wavelength (photon energy) corresponding to …
Spectrochemical Series
The spectrochemical series is an empirically determined ranking of ligands in order of their ability to split the d-orbital energy levels of a transition metal ion (crystal field s…
Spectroscopy
The study of the interaction between matter and electromagnetic radiation. Different spectroscopic techniques (UV-Vis, IR, NMR, mass spectrometry) provide information about molecul…
Spectrum
In chemistry and physics, a spectrum is the distribution of electromagnetic radiation emitted, absorbed, or scattered by a substance as a function of wavelength or frequency. Atomi…
Spin
Spin is an intrinsic quantum mechanical property of particles (electrons, protons, neutrons, quarks) that has no classical analogue but behaves like angular momentum. For electrons…
Spin Quantum Number
The quantum number (ms) that describes the intrinsic angular momentum (spin) of an electron, with values of +½ (spin up ↑) or -½ (spin down ↓). The Pauli exclusion principle requir…
Spontaneous Process
A spontaneous process is a process that occurs naturally without continuous external intervention under a given set of conditions. Spontaneity is governed by the Gibbs free energy:…
Spontaneous Reaction
A reaction that proceeds in a given direction without requiring continuous external energy input under specified conditions. Spontaneity is determined by the sign of ΔG: negative Δ…
Square Planar
Square planar is a molecular geometry in which a central atom is surrounded by four atoms or groups positioned at the corners of a square in the same plane as the central atom, giv…
Square Planar Complex
A square planar complex is a type of coordination compound in which four ligands are arranged around the central metal ion at the corners of a square, with the metal at the center …
Standard Conditions
Reference conditions used for comparing thermodynamic quantities: 298 K (25°C), 1 bar (100 kPa) pressure, and 1 M for solutions. Standard state thermodynamic quantities are denoted…
Standard Electrode Potential
The standard electrode potential (E°) is the potential of a half-cell measured relative to the standard hydrogen electrode (SHE = 0 V) under standard conditions (1 M solution, 298 …
Standard Electrode Potential
The electrode potential measured under standard conditions (25°C, 1 M, 1 atm) relative to the standard hydrogen electrode (SHE = 0 V). Used to predict the direction of spontaneous …
Standard Electrodes
Standard electrodes are half-cells in which all species are in their standard states (unit activity, 1 M for solutions, 1 atm for gases) and the electrode potential is measured rel…
Standard Enthalpy of Formation
The enthalpy change when one mole of a compound is formed from its elements in their standard states at 298 K. Symbol: ΔHf°. Elements in their standard state have ΔHf° = 0 by defin…
Standard Entropy
Standard entropy (S°) is the absolute entropy of one mole of a pure substance at standard conditions (298 K, 1 bar), measured in J mol⁻¹ K⁻¹. Unlike enthalpy, absolute entropies ca…
Standard Gibbs Energy
The Gibbs free energy change for a reaction under standard conditions (298 K, 1 bar, 1 M). Calculated from standard enthalpy and entropy: ΔG° = ΔH° - TΔS°. Related to the equilibri…
Standard Molar Enthalpy Of Formation
The standard molar enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states (pure substan…
Standard Molar Volume
The standard molar volume is the volume occupied by one mole of an ideal gas at standard conditions. At STP (0°C, 1 atm) the standard molar volume is 22.414 L/mol; at SATP (25°C, 1…
Standard Reaction
A standard reaction refers to a chemical reaction carried out under standard conditions — typically 298 K (25°C), 1 bar pressure, and unit activity (1 M for dissolved species). The…
Standard Solution
A solution of precisely known concentration used in analytical chemistry, especially in titrations. Primary standard solutions are made by dissolving a known mass of a primary stan…
State Function
A thermodynamic property that depends only on the current state (pressure, temperature, composition) of a system, not on the path by which that state was reached. Examples include …
States of Matter
The distinct forms in which matter exists, primarily solid, liquid, and gas. A fourth state, plasma, exists at very high temperatures. Each state has characteristic properties dete…
Stereochemistry
The branch of chemistry concerned with the three-dimensional arrangement of atoms in molecules and how this affects chemical reactions. Stereochemistry includes the study of stereo…
Stereoisomers
Stereoisomers are isomers that have the same molecular formula and the same connectivity (sequence of bonds) between atoms but differ in the three-dimensional spatial arrangement o…
Stoichiometric
Relating to the exact proportions of reactants and products in a balanced chemical equation. A stoichiometric amount is the theoretically required amount based on mole ratios. Stoi…
Stoichiometry
Stoichiometry is the quantitative study of the relationships between reactants and products in chemical reactions based on the conservation of mass and balanced equations. It uses …
Stoichiometry
The calculation of quantitative relationships between reactants and products in chemical reactions based on the balanced equation. Uses mole ratios from the balanced equation as co…
Strong Acid
An acid that completely dissociates into ions in aqueous solution. Examples include HCl, HBr, HI, HNO₃, H₂SO₄, and HClO₄. In dilute solutions, virtually no undissociated acid molec…
Strong Base
A base that completely dissociates in aqueous solution to give OH⁻ ions. Examples include NaOH, KOH, Ca(OH)₂, and Ba(OH)₂. Strong bases react completely with strong acids in neutra…
Strong Electrolyte
A strong electrolyte is a substance that dissociates completely into ions when dissolved in water, producing a solution that conducts electricity well. Examples include all soluble…
Strong Electrolyte
A substance that completely dissociates into ions when dissolved in water, producing a highly conductive solution. Strong electrolytes include strong acids (HCl, HNO₃), strong base…
Strong Field Ligand
A strong-field ligand is a ligand that causes a large crystal field splitting (Δ) of the d-orbital energy levels of the central metal ion, favoring the pairing of electrons in lowe…
Strontium
Strontium is a soft, silvery alkaline earth metal, atomic number 38. Named after Strontian, Scotland. Notable for its brilliant crimson flame colour used in fireworks. Radioactive …
Structural Formula
A chemical formula showing how atoms are connected in a molecule. Condensed structural formulas show connectivity without showing all bonds; expanded (full) structural formulas sho…
Structural Isomers
Structural isomers (constitutional isomers) are molecules that have the same molecular formula but different connectivity — the atoms are bonded in a different order or arrangement…
Structural Isomers
Isomers with the same molecular formula but different connectivity (different bonding arrangements) of atoms. Types include chain isomers, position isomers, and functional group is…
Sublimation
Sublimation is the direct transition of a substance from the solid phase to the gas phase without passing through the liquid phase, at pressures below the substance's triple point.…
Sublimation
The phase transition in which a solid changes directly to a gas without passing through the liquid state. It requires energy equal to the sum of enthalpy of fusion and enthalpy of …
Subshell
A group of orbitals with the same principal quantum number (n) and angular momentum quantum number (l). Subshells are designated s (l=0, 1 orbital), p (l=1, 3 orbitals), d (l=2, 5 …
Substance
In chemistry, a substance (pure substance) is matter with a uniform and definite composition throughout, which cannot be separated into other kinds of matter by any physical means.…
Substitution Reaction
A substitution reaction is a type of organic reaction in which one atom or group of atoms in a molecule is replaced by another atom or group. In nucleophilic substitution (SN1 and …
Substitution Reaction
A chemical reaction in which one atom or group in a molecule is replaced by another atom or group. Types include nucleophilic substitution (SN1, SN2), electrophilic aromatic substi…
Substrate
The molecule upon which an enzyme acts in a biochemical reaction. The substrate binds to the enzyme's active site, forming an enzyme-substrate complex. The enzyme catalyzes convers…
Sulfur
Sulfur is a bright yellow non-metal, atomic number 16. Found in nature as elemental deposits and in sulfide/sulfate minerals. Odourless as element. Essential for life as component …
Sulfuric Acid
Sulfuric acid (H₂SO₄) is a highly corrosive, oily, diprotic strong acid that is one of the most important industrial chemicals, produced globally in greater quantities than any oth…
Supercooled Liquids
A supercooled liquid is a liquid that has been cooled below its normal freezing point without solidifying, remaining in a metastable liquid state due to the absence of nucleation s…
Supercritical Fluid
A supercritical fluid is a substance maintained above both its critical temperature and critical pressure, where distinct liquid and gas phases do not exist. Supercritical fluids h…
Supercritical Fluid
A substance at a temperature and pressure above its critical point, where it has properties intermediate between a liquid and a gas. Supercritical CO₂ is used as a green solvent fo…
Supersaturated Solution
A supersaturated solution is an unstable solution that contains more dissolved solute than is present in a saturated solution at the same temperature, prepared by carefully cooling…
Surface Area
The total area of the surface of a solid or liquid. Increasing surface area increases reaction rate by exposing more reactant molecules to collision. This is why powdered solids re…
Surface Tension
Surface tension is the elastic tendency of liquid surfaces to acquire the minimum surface area. It arises because molecules at the surface experience a net inward force (cohesion) …
Surface Tension
The tendency of liquid surfaces to contract and resist rupture, caused by cohesive forces between surface molecules. Surface tension allows insects to walk on water and causes capi…
Surroundings
Everything outside the system in a thermodynamic analysis. Energy can flow between the system and its surroundings as heat or work. In an open system, matter can also exchange. The…
Suspension
A heterogeneous mixture in which relatively large solid particles are dispersed in a liquid or gas. Unlike colloids, suspended particles eventually settle under gravity. They can b…
Suspension
A mixture in which solid particles are temporarily dispersed in a fluid but will eventually settle due to gravity. Unlike colloids, suspended particles are large enough to be seen …
System
The part of the universe chosen for thermodynamic analysis. Open systems exchange both matter and energy with surroundings; closed systems exchange only energy; isolated systems ex…
About Chemicals Starting With S
This page lists all chemicals in our database beginning with the letter S. Each entry provides the chemical formula, CAS registry number, physical and chemical properties, common uses, and safety information. Use the alphabetical navigation above to browse other letters, or use the search function to find a specific chemical quickly.
Our chemical glossary covers acids, bases, salts, organic compounds, inorganic compounds, solvents, and many more categories. Click on any chemical name to view its full detailed profile.