# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
S
salt bridge: A pathway between two half-cells of an electrochemical cell that allows the passage of ions from one half-cell to the other.
saturated air: Air that contains water vapour and cannot retain any more.
saturated solution: A solution that contains the maximum amount of solute possible.
secondary colours of light or pigments: These are formed by mixing pairs of primary colours. The secondary colours of light are magenta, yellow and cyan. The secondary colours of pigments are blue, green and red.
sediment: Weathered material derived from pre-existing rocks.
sedimentary rock: A rock composed of sediment. The sediment may contain particles of various sizes, such as gravel or sand, or the remains of plants or animals, as in coal and some limestones, or be derived from chemicals in solution by organic or inorganic processes.
sedimentation: A technique for separating mixtures in which a solid in solution is allowed to settle through gravity.
seismic wave: Waves produced by an explosion, such as an earthquake, that move through the interior or surface of Earth.
seismogram: A record of a seismic wave, drawn on graph paper.
seismograph: An instrument that detects seismic waves.
seismology: The study of earthquakes.
semi-structural diagram: A diagram that shows the bonds between atoms only as straight lines. The atoms are represented by their atomic symbols.
series circuit: An electric circuit with only one conducting path.
shell: An energy level in an atom where electrons may be found.
short circuit: A conducting path in an electric circuit of very low resistance. A high current flows in short circuits.
sidereal: With respect to the stars.
sidereal time: Equivalent to the right ascension of stars on the observer’s meridian.
sliding friction: A friction force that tends to slow a sliding object.
solar energy: Another name for radiant energy given off by the Sun.
solar radiation: The common name give to electromagnetic radiation emitted by the Sun.
solar time: A system of keeping time by gauging the position of the Sun over Earth.
solidification: A change of state from a liquid or gas to a solid.
solubility: A measure of the amount of solute dissolved in a given amount of solvent or solution, at a given temperature.
soluble: The ability of a substance to dissolve in a solvent.
solute: A substance that dissolves in a solvent (e.g. sugar).
solution: A mixture of a solvent and a solute.
solvent: A substance, usually a liquid, which is able to dissolve a solute (e.g. water).
sound: A travelling vibration or wave through a material medium.
spark: The movement of electrons, usually in the air, from one material to another.
specific gravity: The density of a substance compared to the density of water.
specific heat capacity: A measure of a substance’s resistance to increased temperature.
spectra (absorption): This is when light passes through a substance and is separated into its various colours. The substance will absorb certain colours according to its molecular or atomic structure.
spectral analysis: A study of spectra to determine the molecular or atomic structure of substances.
spectrum: The colours of the rainbow: red, orange, yellow, green, blue, indigo and violet.
specular reflection: The reflection of light off smooth polished surfaces such as mirrors. A light beam will specularly reflect off a mirror in one direction.
stable octet: The rule where the atom is considered stable if it has eight electrons in its outer shell.
static electricity: A phenomenon that involves the separation of electric charges. This is also called ‘electrostatics’.
static friction: A friction force that keeps a stationary object from moving.
stir-thickening liquid: A rheopectic fluid.
stir-thinning liquid: A thixotropic fluid.
stratosphere: The second layer of the atmosphere.
structural diagram: A diagram of a molecule where atoms are represented by their atomic symbols and bonding and non-bonding electrons are shown as straight lines.
sub-atomic particles: Particles smaller than atoms. These are protons (positive charge), electrons (negative charge) and neutrons (neutral charge), which are the constituents of atoms.
subduction: A process in which one plate moves under another.
subduction zone: The place where the process of subduction occurs.
sublimation: A change of state from a solid to a gas, without passing through a liquid state.
sunspot: A relatively dark area on the Sun’s surface that is relatively cool.
supernova: An exploding star.
super-saturated solutions: A solution that holds more solute than it can keep dissolved in solution.
surface tension: The ‘skin’ effect on the surfaces of liquids as a result of the attractions between the atoms or molecules within the liquid.
surface wave: A seismic wave that is a transverse wave over the surface of Earth.
surfactant: A chemical, such as a detergent or emulsifier, that changes the properties of a surface (e.g. a chemical that alters surface tension).
suspension: A mixture of solid particles and a liquid where the particles are too large to remain in solution and so, after some time, they settle on the bottom of the container that holds the liquid.
S wave: A secondary wave. A transverse seismic wave that is slower than a P wave.
syzygy: The alignment of three celestial bodies.