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
191 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…
Safranin
Safranin O is an organic chloride salt having 3,7-diamino-2,8-dimethyl-5-phenylphenazin-5-ium as the counterion. It is commonly used for staining Gram negative bacteria. It has a r…
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…
Salicylic acid
Salicylic acid is a monohydroxybenzoic acid that is benzoic acid with a hydroxy group at the ortho position. It is obtained from the bark of the white willow and wintergreen leaves…
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 …
Scandium(III) triflate
Scandium(III) triflate (CHF3O3SSc) is a laboratory reagent. It has a molecular weight of 195.04 g/mol. Its IUPAC name is scandium;trifluoromethanesulfonic acid.
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 …
Sebacic acid
Sebacic acid is an alpha,-dicarboxylic acid that is the 1,8-dicarboxy derivative of octane. It has a role as a plant metabolite and a human metabolite. It is a dicarboxylic fatty a…
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 …
Selenium dioxide
Selenium dioxide (O2Se) is a laboratory reagent that appears as Selenium dioxide appears as a white or creamy-white volatile lustrous crystal or crystalline powder with a pungent s…
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 …
Serotonin
Serotonin is a primary amino compound that is the 5-hydroxy derivative of tryptamine. It has a role as a neurotransmitter, a mouse metabolite and a human metabolite. It is a monoam…
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…
Sildenafil
Sildenafil is a pyrazolo[4,3-d]pyrimidin-7-one having a methyl substituent at the 1-position, a propyl substituent at the 3-position and a 2-ethoxy-5-[(4-methylpiperazin-1-yl)sulfo…
Silica gel
Silicon dioxide is a silicon oxide made up of linear triatomic molecules in which a silicon atom is covalently bonded to two oxygens.
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…
Silicon carbide
Silicon carbide (CSi) is an inorganic compound that appears as Silicon carbide appears as yellow to green to bluish-black, iridescent crystals. Sublimes with decomposition at 2700 …
Silicon dioxide
Silicon dioxide is a silicon oxide made up of linear triatomic molecules in which a silicon atom is covalently bonded to two oxygens.
Silicon tetrachloride
Silicon tetrachloride (SiCl4) is an inorganic compound that appears as Silicon tetrachloride is a colorless, fuming liquid with a pungent odor. It is decomposed by water to hydroch…
Silicone rubber
Silicone rubber is an elastomeric polymer based on a silicon-oxygen backbone (–Si(CH₃)₂–O–)n, also known as polydimethylsiloxane (PDMS) in its simplest form. Unlike carbon-based ru…
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,…
Silver nitrate
Silver(1+) nitrate is a silver salt and an inorganic nitrate salt. It has a role as a NMR chemical shift reference compound and an astringent.
Silver oxide
Silver oxide (Ag2O) is an inorganic compound that appears as Silver oxide is an odorless brown-black solid. Sinks in water. (USCG, 1999). It has a molecular weight of 231.736 g/mol…
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…
Skatole
Skatole is a methylindole carrying a methyl substituent at position 3. It is produced during the anoxic metabolism of L-tryptophan in the mammalian digestive tract. It has a role a…
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…
Sodium acetate
Sodium acetate (C2H3NaO2) is a salt that appears as Dry Powder; Liquid; Pellets or Large Crystals. It has a molecular weight of 82.03 g/mol. Melting point: 324 °C.
Sodium amide
Sodium amide is an inorganic sodium salt composed of a sodium cation and an azanide anion. It is used as a strong base in organic synthesis. It has a role as a catalyst and a nucle…
Sodium azide
Sodium azide is the sodium salt of hydrogen azide (hydrazoic acid). It has a role as a mitochondrial respiratory-chain inhibitor, a mutagen, an antibacterial agent and an explosive…
Sodium bicarbonate
Sodium hydrogencarbonate is an organic sodium salt and a one-carbon compound. It has a role as an antacid and a food anticaking agent. It contains a hydrogencarbonate.
Sodium borohydride
Sodium borohydride (NaBH4) is a salt that appears as Sodium borohydride is a white to grayish crystalline powder. It is decomposed by water to form sodium hydroxide, a corrosive ma…
Sodium carbonate
Sodium carbonate (Na2CO3) is a base or alkali that appears as Other Solid; Liquid, Other Solid; Dry Powder; Water or Solvent Wet Solid; Liquid; Pellets or Large Crystals; Dry Powde…
Sodium chloride
Sodium chloride is an inorganic chloride salt having sodium(1+) as the counterion. It has a role as an emetic, a NMR chemical shift reference compound and a flame retardant. It is …
Sodium cyanide
Sodium cyanide is a cyanide salt containing equal numbers of sodium cations and cyanide anions. It has a role as an EC 1.15.1.1 (superoxide dismutase) inhibitor. It is a sodium sal…
Sodium cyanoborohydride
Sodium cyanoborohydride (CH3BNNa) is a laboratory reagent that appears as White hygroscopic solid; [Merck Index] White powder; [Alfa Aesar MSDS]. It has a molecular weight of 62.84…
Sodium dihydrogen phosphate
Sodium dihydrogen phosphate (NaH2PO4) is a salt that appears as Pellets or Large Crystals; Dry Powder, Pellets or Large Crystals; Dry Powder, Liquid; NKRA; Other Solid; Dry Powder,…
Sodium fluoride
Sodium fluoride is a metal fluoride salt with a Na(+) counterion. It has a role as a mutagen.
Sodium hydroxide
Sodium hydroxide (NaOH) is a base or alkali that appears as Sodium hydroxide solution appears as a colorless liquid. More dense than water. Contact may severely irritate skin, eyes…
Sodium hypochlorite
Sodium hypochlorite is an inorganic sodium salt in which hypochlorite is the counterion. It is used as a bleaching and disinfecting agent and is commonly found in household bleach.…
Sodium iodide
Sodium iodide is a metal iodide salt with a Na(+) counterion. It is an iodide salt and an inorganic sodium salt.
Sodium methoxide
Sodium methoxide (CH3NaO) is a base or alkali that appears as Sodium methylate is a white amorphous powder. It reacts with water to form sodium hydroxide, a corrosive material, and…
Sodium molybdate
Sodium molybdate (anhydrous) is an inorganic sodium salt having molybdate as the counterion. It has a role as a NMR chemical shift reference compound and a poison. It contains a mo…
Sodium nitrate
Sodium nitrate is the inorganic nitrate salt of sodium. It has a role as a fertilizer. It is an inorganic sodium salt and an inorganic nitrate salt.
Sodium periodate
Sodium periodate is an inorganic sodium salt having periodate as the counterion. It has a role as an oxidising agent. It contains a periodate.
Sodium peroxide
Sodium peroxide (Na2O2) is an inorganic compound that appears as Sodium peroxide appears as a yellow-white to yellow granular solid. Mixtures with combustible material are readily …
Sodium phosphate tribasic
Sodium phosphate tribasic (Na3PO4) is a salt that appears as Sodium phosphate, tribasic appears as a colorless to white crystalline solid. Noncombustible.. It has a molecular weigh…
Sodium silicate
Sodium silicate is an inorganic sodium salt having silicate as the counterion. It contains a silicate ion.
Sodium sulfate
Sodium sulfate (Na2SO4) is a salt that appears as Gas or Vapor; Dry Powder, Pellets or Large Crystals; Pellets or Large Crystals; Water or Solvent Wet Solid; Dry Powder; Dry Powder…
Sodium sulfite
Sodium sulfite is an inorganic sodium salt having sulfite as the counterion. It has a role as a reducing agent and a food preservative. It is an inorganic sodium salt and a sulfite…
Sodium tartrate
Sodium L-tartrate is the organic sodium salt that is the disodium salt of L-tartaric acid. It has a role as a food emulsifier. It contains a L-tartrate(2-).
Sodium thiosulfate
Sodium thiosulfate pentahydrate is a hydrate consisting of sodium thiosulfate with 5 mol eq. of water. It has a role as a nephroprotective agent, an antifungal drug and an antidote…
Sodium tungstate
Sodium tungstate is an inorganic sodium salt having tungstate as the counterion. Combines with hydrogen peroxide for the oxidation of secondary amines to nitrones. It has a role as…
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,…
Sorbitol
D-glucitol is the D-enantiomer of glucitol (also known as D-sorbitol). It has a role as a metabolite, a laxative, a sweetening agent, a cathartic, a mouse metabolite, a Saccharomyc…
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…
Squalene
Squalene is a triterpene consisting of 2,6,10,15,19,23-hexamethyltetracosane having six double bonds at the 2-, 6-, 10-, 14-, 18- and 22-positions with (all-E)-configuration. It ha…
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…
Starch
Starch is a natural polysaccharide produced by plants as an energy storage molecule. It consists of two components: amylose (a linear polymer of α-1,4-linked glucose, typically 20–…
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…
Stearic acid
Octadecanoic acid is a C18 straight-chain saturated fatty acid component of many animal and vegetable lipids. As well as in the diet, it is used in hardening soaps, softening plast…
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…
Streptomycin
Streptomycin is a amino cyclitol glycoside that consists of streptidine having a disaccharyl moiety attached at the 4-position. The parent of the streptomycin class. It has a role …
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 …
Strontium chloride
Strontium dichloride is an inorganic chloride and a strontium salt. It has a role as a NMR chemical shift reference compound.
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…
Styrene
Styrene is a vinylarene that is benzene carrying a vinyl group. It has been isolated from the benzoin resin produced by Styrax species. It has a role as a mutagen, a mouse metaboli…
Styrene-butadiene rubber
Styrene-butadiene rubber (C12H14) is a polymer or plastic that appears as Other Solid; Liquid. It has a molecular weight of 158.24 g/mol. Its IUPAC name is buta-1,3-diene;styrene.
Suberic acid
Suberic acid is an alpha,-dicarboxylic acid that is the 1,6-dicarboxy derivative of hexane. It has a role as a human metabolite. It is a dicarboxylic fatty acid and an alpha,omega-…
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…
Succinic acid
Succinic acid is an alpha,-dicarboxylic acid resulting from the formal oxidation of each of the terminal methyl groups of butane to the corresponding carboxy group. It is an interm…
Succinic anhydride
Succinic anhydride is a cyclic dicarboxylic anhydride and a tetrahydrofurandione. It is functionally related to a succinic acid.
Sucrose
Sucrose is a glycosyl glycoside formed by glucose and fructose units joined by an acetal oxygen bridge from hemiacetal of glucose to the hemiketal of the fructose. It has a role as…
Sulfolane
Sulfolane is a member of the class of tetrahydrothiophenes that is tetrahydrothiophene in which the sulfur has been oxidised to give the corresponding sulfone. A colourless, high-b…
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 …
Sulfur dioxide
Sulfur Dioxide can cause developmental toxicity according to an independent committee of scientific and health experts.
Sulfur hexafluoride
Sulfur hexafluoride is a sulfur coordination entity consisting of six fluorine atoms attached to a central sulfur atom. It is the most potent greenhouse gas currently known, with a…
Sulfur trioxide
Sulfur trioxide (O3S) is an inorganic compound that appears as Sulfur trioxide, is a colorless to white crystalline solid which will fume in air. Often shipped with inhibitor to pr…
Sulfuric acid
Sulfuric acid is a sulfur oxoacid that consists of two oxo and two hydroxy groups joined covalently to a central sulfur atom. It has a role as a catalyst. It is a conjugate acid of…
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…
Sulfurous acid
Sulfurous acid is a sulfur oxoacid. It is a conjugate acid of a hydrogensulfite. It is a tautomer of a sulfonic acid.
Sulfuryl chloride
Sulfuryl chloride (SO2Cl2) is an inorganic compound that appears as Sulfuryl chloride appears as a colorless fuming liquid with a pungent odor. Very toxic by inhalation. Corrosive …
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.