Glossary of chemical terms

s.t.p.
	Standard temperature (273.15 K) and pressure (101 325 Pa) is the standard conditions used as a basis for calculations involving quantities that vary with temperature and pressure. These conditions are used when comparing the properties of gases.
salinity
	Salinity (S) is a parameter used in oceanography to describe the concentration of dissolved salts in seawater. The salinity of normal seawater is 35 parts salt per 1000 parts water.
salt
	Salt is an ionic compound formed by the reaction of an acid and a base. The reaction of sodium hidroxide to hydrochloric acid give sodium chloride NaOH + HCl NaCl + H2O
salt bridge
	Salt bridge is a permeable material soaked in a salt solution that allows ions to be transferred from one container to another. The salt solution remains unchanged during this transfer.
saturated solution
	Saturated solution is a solution that holds the maximum possible amount of dissolved material. When saturated, the rate of dissolving solid and that of recrystallisation solid are the same, and a condition of equilibrium is reached. The amount of material in solution varies with the temperature; cold solutions can hold less dissolved solid material than hot solutions. Gases are more soluble in cold liquids than in hot liquids.
Schiff base
	Schiff base is a class of compounds derived by chemical reaction (condesation) of aldehydes or ketones with aromatic amines, for example RNH2 + R'CHO RN:CHR' + H2O They are named after the German chemist Hugo Schiff (1834-1915).
Schrödinger equation
	Schrödinger equation is the basic equation of wave mechanics which, for systems not dependent on time, takes the form: where Ψ is the wavefunction, V is the potential energy expressed as a function of the spatial coordinates, E its total energy, 2 is the Laplacian operator, h is Planck's constant, and m is the mass.
second
	Second (s) is the SI base unit of time. The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels (F = 4, mF = 0 to F = 3, mF = 0) of the ground state of the caesium 133 atom.
selenides
	Selenides are compounds having the structure RSeR (R not equal to H). They are thus selenium analogues of ethers. Also used for metal salts of H2Se.
semiconductor
	Semiconductor is a material in which the highest occupied energy band (valence band) is completely filled with electrons at T = 0 K, and the energy gap to the next highest band (conduction band) ranges from 0 to 4 or 5 eV. With increasing temperature electrons are excited into the conduction band, leading to an increase in the electrical conductivity.
semimetal
	See Metalloid
SI units
	See International System of Units
siemens
	Siemens (S) is the SI derived unit of of electrical conductance of a conductor in which a current of one ampere is produced by an electrical potential difference of one volt (S = A∙V-1 = Ω-1). The unit is named after the German scientist Ernst Werner von Siemens (1816-1892).
sievert
	Sievert (Sv) is the SI derived unit of dose equivalent when the absorbed dose of ionizing radiation multiplied by the stipulated dimensionless factors is 1 J/kg. It is named after the Swedish physicst Rolf Sievert (1896-1966).
significant figures
	Measurements are not infinitely accurate: we must estimate measurement uncertainty. The number of significant figures is all of the certain digits plus the first uncertain digit. Rules for significant figures: 1. Disregard all initial zeros. 2. Disregard all final zeros unless they follow a decimal point. 3. All remaining digits including zeros between nonzero digits are significant. 0.0023 have two significant figures 0.109 have three significant figures 2.00 have three significant figures 70 have one significant figure In adition and subtraction, the number of significant figures in the answer depends on the original number in the calculation that has the fewest digits to the right of the decimal point. In multiplication and division, the number of significant figures in a calculated result is determined by the original measurement that has the fewest number of significant digits. In a logarithm of a number, keep as many digits to the right of the decimal point as there are significant figures in the original number. In an antilogarithm of a number, keep as many digits as there are digits to the right of the decimal point in the original number.
silanes
	Silanes are saturated silicon hydrides, analogues of the alkanes (compounds of the general formula SinH2n+2).
silicones
	Silicones are polymeric or oligomeric siloxanes, usually considered unbranched, of general formula [-OSiR2-]n (R not equal to H).
siloxanes
	Siloxanes are saturated silicon-oxygen hydrides with unbranched or branched chains of alternating silicon and oxygen atoms (-Si-O-Si-).
smog
	Smog is a mixture of smoke and fog. The term is used to describe city fogs in which there is a large proportion of particulate matter (tiny pieces of carbon from exhausts) and also a high concentration of sulphur and nitrogen gases.
sol
	Sols are dispersions of small solid particles in a liquid. The particles may be macromolecules or may be clusters of small molecules. Lyophobic sols are those in which there is no affinity between the dispersed phase and the liquid (e.g. silver chloride dispersed in water). Lyophobic sols are inherently unstable, in time the particles aggregate, and form a precipitate. Lyiophilic sols, on the other hand, are more like true solutions in which the solute molecules are large and have an affinity for the solvent (e.g. starch in water). Association colloids are systems in which the dispersed phase consists of clusters of molecules that have lyophobic and lyophilic parts (e.g. soap in water).
solubility
	Solubility is the maximum amount of solute that dissolves in a given quantity of solvent at a specific temperature. Generally, for a solid in a liquid, solubility increases with temperature; for a gas, solubility decreases. Common measures of solubility include the mass of solute per unit mass of solution (mass fraction), mole fraction of solute, molality, molarity, and others.
solubility product constant
	Solubility product constant (Ksp) (or the solubility product) is the product of the molar concentrations of the constituent ions, each raised to the power of its stoichiometric coefficient in the equilibrium equation. For instance, if a compound AaBb is in equilibrium with its solution AaBb(s) aA+ + bB the solubility product is given by Ksp(AaBb) = [A+]a∙[B-]b
specific gravity
	Specific gravity is ratio of the density of a material to that density of a water. Since one must specify the temperature of both the sample and the water to have a precisely defined quantity, the use of this term is now discouraged.
specific heat
	Specific heat is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius.
specific quantity
	Specific quantity is often convenient to express an extensive quantity (e.g., volume, enthalpy, heat capacity, etc.) as the actual value divided by mass. The resulting quantity is called specific volume, specific enthalpy, etc.
standard electrode potential
	Standard electrode potential (E°) (standard reduction potentialis) are defined by measuring the potential relative to a standard hydrogen electrode using 1 mol solution at 25 °C. The convention is to designate the cell so that the oxidized form is written first. For example, Pt(s)|H2(g)H+(aq)|Zn2+(aq)|Zn(s) The e.m.f. of this cell is -0.76 V and the standard electrode potential of the Zn2+|Zn half cell is -0.76 V.
standard hydrogen electrode
	Standard hydrogen electrode is a system in which hydrogen ion and gaseous hydrogen are present in their standard states. The convention is to designate the cell so that the standard hydrogen electrode is written first. H2(g) 2H+(aq) + 2e- The electrode is used as a reference (of zero) for the values of other standard electrode potentials.
standard mean ocean water
	Standard mean ocean water (SMOW) is a standard sample of pure water of accurately known isotopic composition which is maintained by the International Atomic Energy Agency. It is used for precise calibration of density and isotopic composition measurements.
standards
	Standards are materials containing a known concentration of an analyte. They provide a reference to determine unknown concentrations or to calibrate analytical instruments. The accuracy of an analytical measurement is how close a result comes to the true value. Determining the accuracy of a measurement usually requires calibration of the analytical method with a known standard. This is often done with standards of several concentrations to make a calibration or working curve. A primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has a high molecular weight. A secondary standard is a standard that is prepared in the laboratory for a specific analysis. It is usually standardized against a primary standard.
stoichiometric number
	Stoichiometric number (ν) is the number appearing before the symbol for each compound in the equation for a chemical reaction. By convention, it is negative for reactants and positive for products.
stoichiometry
	Stoichiometry is the relative proportions in which elements from compounds or in which substances react. Every chemical reaction has its characteristic proportions. For example, when methane unites with oxygen in complete combustion, 1 mol of methane requires 2 mol of oxygen. CH4 + 2O2 CO2 + 2H2O At the same time, 1 mol of carbon dioxide and 2 mol of water are formed as reaction productions. Alternatively, 16 g of methane and 64 g of oxygen produce 44 g of carbon dioxide and 36 g of water.
stratosphere
	Stratosphere is the part of the earth's atmosphere extending from the top of the troposphere (typically 10 km to 15 km above the surface) to about 50 km. It is characterized by an increase in temperature with increasing altitude.
superconductor
	Superconductor is a material that experiences a nearly total loss of electrical resistivity below a critical temperature Tc.
superfluid
	Superfluid is a fluid with near-zero viscosity and extremely high thermal conductivity. Liquid helium exhibits these properties below 2.186 K (the λ point).

 

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