| Salt |
an ionic compound |
| Salt bridge |
a tube containing an electrolyte that connects the two
compartments of a galvanic cell, allowing ion flow without extensive mixing of the
different solutions |
| Saturated Solution |
A solution containing the maximum amount of solute that a
given quantity of solvent can dissolve at a given temperature; a solution in which
equilibrium exists between the dissolved and undissolved solute |
| Scientific method |
the process of studying natural phenomena, involving
observations, forming laws and theories, and testing of theories by experimentation |
| Scintillation counter |
an instrument that measures radioactive decay by sensing the
flashes of light produced in a substance by the radiation |
| Screening Effect |
Reduction of the attraction between the nuclear charge and
the highest-energy-level electrons, caused by the presence of electrons in lower energy
levels |
| Second law of thermodynamics |
in any spontaneous process, there is always an increase in
the entropy of the universe |
| Second-Order Rate Equation |
A rate equation in which the rate is proportional to the
second power of the concentration of one reactant or to the first power of the
concentration of each of two reactants |
| Secondary structure (of a protein) |
the three-dimensional structure of the protein chain (for
example, a-helix, random coil, or pleated sheet) |
| Sedimentary Rocks |
Rocks formed on the earth's surface or sea floor from small
particles or dissolved substances from other rocks |
| Selective precipitation |
a method of separating metal ions from an aqueous mixture by
using a reagent whose anion forms a precipitate with only one or a few of the ions in the
mixture |
| Semiconductor |
a substance conducting only a slight electrical current at
room temperature, but showing increased conductivity at higher temperatures |
| Semipermeable Membrane |
A membrane that allows the passage of only some components of
a solution |
| Shielding |
the effect by which the other electrons screen, or shield, a
given electron from some of the nuclear charge |
| Sl units |
International System of units based on the metric system and
units derived from the metric system |
| Side chain (of amino acid) |
the hydrocarbon group on an amino acid represented by H, CH3,
or a more complex substituent |
| Sigma Bond |
A covalent bond in which the electron density is symmetrical
about the internuclear axis |
| Significant figures |
the certain digits and the first uncertain digit of a
measurement |
| Silica |
the fundamental silicon-oxygen compound, which has the
empirical formula SiO2, and forms the basis of quartz and certain types of sand |
| Silicates |
salts that contain metal cations and polyatomic
siticon-oxygen anions that are usually polymeric |
| Single Bond |
a bond in which one pair of electrons is shared by two atoms |
| Singlet |
An electron energy state in which electron spins are all
paired |
| Smelting |
a metallurgical process that involves reducing metal ions to
the free metal |
| Solid Solution |
A homogeneous solid mixture |
| Solubility |
the amount of a substance that dissolves in a given volume of
solvent at a given temperature |
| Solubility product constant |
the constant for the equilibrium expression representing the
dissolving of an ionic solid in water |
| Solute |
a substance dissolved in a liquid to form a solution |
| Solution |
a homogeneous mixture |
| Solvent |
the dissolving medium in a solution |
| Somatic damage |
radioactive damage to an organism resulting in its sickness
or death ( |
| Space-filling model |
a model of a molecule showing the relative sizes of the atoms
and their relative orientations |
| Specific heat capacity |
The amount of energy required to elevate the temperature of
one gram of a substance one degree Celsius |
| Spectator Ions |
Ions present in a solution that do not participate in a
chemical reaction |
| Spectrochemical series |
a listing of ligands in order based on their ability to
produce d-orbital splitting |
| Spectrophotometer |
An instrument for measuring the intensity of radiation
absorbed at different wavelengths |
| Spectroscope |
A device for dispersing radiation into a spectrum so that the
component wavelengths can be observed |
| Spectrum |
An array of the components of radiation separated in order of
some varying property such as wavelength |
| Spin Quantum Number |
The quantum number that specifies the spin state of an
electron |
| Spontaneous fission |
the spontaneous splitting of a heavy nuclide into two lighter
nuclides |
| Spontaneous process |
a process that occurs without outside intervention |
| Standard atmosphere |
a unit of pressure equal to 760 mm Hg |
| Standard Electrode Potential |
The potential of a half-cell when all reactants are present
in their standard states relative to the standard hydrogen electrode Normally, standard
electrode potentials are for reduction reactions |
| Standard Electromotive Force |
The potential of' a cell when all reactants are present in
their standard states |
| Standard enthalpy of formation |
the enthalpy change that accompanies the formation of one
mote of a compound at 25oC from its elements, with all substances in their
standard states at that temperature |
| Standard free energy change |
the change in free energy that will occur for one unit of
reaction if the reactants in their standard states are converted to products in their
standard states |
| Standard free energy of formation |
the change in free energy that accompanies the formation of
one mole of a substance from its constituent elements with all reactants and products in
their standard states |
| Standard reduction potential |
the potential of a half-reaction under standard state
conditions, as measured against the potential of the standard hydrogen electrode |
| Standard State |
A reference state for thermodynamic measurements, defined for
a liquid or solid as the pure substance at one atmosphere external pressure, for a gas as
an ideal gas at one atmosphere pressure, and for a solution as a 1 M solution, in each
case at the specified temperature |
| Standard solution |
a solution whose concentration is accurately known |
| Standard temperature and pressure (STP) |
the condition of 273 K and 1 atm pressure |
| Standing wave |
a stationary wave as on a string of a musical instrument; in
the wave mechanical model, the electron in the hydrogen atom is considered to be a
standing wave |
| State function |
A function whose value depends only on the state of a
substance and not on the path by which the state was reached |
| States of matter |
the three different forms in which matter can exist: solid,
liquid, and gas |
| Steam cracking |
a process whereby hydrocarbon molecules are broken into small
fragments by steam at very high temperatures |
| Stereoisomers |
Isomers differing only in the spatial arrangement of the
atoms |
| Steric factor |
the factor (always less than one) that reflects the fraction
of collisions with orientations that can produce a chemical reaction |
| Steroid |
the factor (always less than one) that reflects the fraction
of collisions with orientations that can produce a chemical reaction |
| Stoichiometry |
The quantitative relationships among the reactants and
products in a chemical reaction as expressed by the equation for the reaction |
| Stoichiometric quantities |
quantities of reactants mixed in exactly the correct amounts
so that all are used up at the same time |
| Storage Cell |
A voltaic cell that is rechargeable by electric energy from
an external source through reversal of the cell reaction |
| Strong acid |
an acid that completely dissociates to produce an H+ ion and
the conjugate base |
| Strong base |
a metal hydroxide salt that completely dissociates into its
ions in water |
| Strong electrolyte |
a material which, when dissolved in water, gives a solution
that conducts an electric current very efficiently |
| Structural formula |
the representation of a molecule in which the relative
positions of the atoms are shown and the bonds are indicated by lines |
| Structural isomerism |
isomerism in which the isomers contain the same atoms but one
or more bonds differ |
| Subcritical reaction (nuclear) |
a reaction in which less than one neutron causes another
fission event and the process dies out |
| Sublimation |
The transformation of a solid directly to a vapor without
forming a liquid |
| Subshell |
a set of orbitals with a given azimuthal quantum number |
| Subsidiary Quantum Number |
The quantum number that specifies the number of nodal planes
passing through the nucleus in the wave function |
| Substitution Reaction |
A reaction in which one atom or group of atoms is replaced by
another |
| Supercooling |
the process of cooling a liquid below its freezing point
without its changing to a solid |
| Supercritical reaction (nuclear) |
a reaction in which more than one neutron from each fission
event causes another fission event The process rapidly escalates to a violent explosion |
| Superheating |
the process of heating a liquid above its boiling point
without its boiling |
| Superoxide |
a compound containing the O2 anion |
| Supersaturated Solution |
An unstable solution containing more solute than a given
amount of solvent can dissolve at a given temperature; a solution in a nonequilibrium
condition in which saturation is exceeded |
| Surface-Active Agent Surfactant |
A substance that acts to reduce surface tension, especially
between hydrophilic and hydrophobic phases |
| Surface tension |
the resistance of a liquid to an increase in its surface area |
| Surfactant |
a wetting agent, such as soap, that assists water in wetting
and suspending nonpolar materials |
| Surroundings |
The portion of matter or space outside that which is under
consideration as a system |
| Syndiotactic chain |
a polymer chain in which the substituent groups such as CH3
are arranged on alternate sides of the chain |
| System (thermodynamic) |
that part of the universe on which attention is to be focused
|
| Systematic error |
an error that always occurs in the same direction |
