Salt

An ionic compound made up of a cation other than H¹ and an anion other than OH² or O²².

Salt Hydrolysis

The reaction of the anion or cation, or both, of a salt with water.

Saponification

Soapmaking.

Saturated Hydrocarbons

Hydrocarbons that contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms present.

Saturated Solution

At a given temperature, the solution that results when the maximum amount of a substance has dissolved in a solvent.

Scientific Method

A systematic approach to research.

Second Ionization Energy

Energy required to remove an electron from a cation.

Second Law of Thermodynamics

The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process.

Second-Order Reaction

A reaction whose rate depends on reactant concentration raised to the second power or on the concentrations of two different reactants, each raised to the first power.

Semiconductors

Elements that normally cannot conduct electricity, but can have their conductivity greatly enhanced either by raising the temperature or by adding certain impurities.

Semipermeable Membrane

A membrane that allows solvent molecules to pass through, but blocks the movement of solute molecules.

Sigma Bond

A covalent bond formed by orbitals overlapping end-to-end; it has its electron density concentrated between the nuclei of the bonding atoms.

Sigma Molecular Orbital

A molecular orbital in which the electron density is concentrated around a line between the two nuclei of the bonding atoms.

Significant Figures

The number of meaningful digits in a measured or calculated quantity.

Single Bond

Two atoms are held together by one electron pair.

Solid

One of three states of matter. A solid has a fixed shape that does not conform to the shape of a container.

Solubility

The maximum amount of solute that can be dissolved in a given quantity of solvent at a specific temperature.

Solubility Product

The product of the molar concentrations of the constituent ions, each raised to the power of its stoichiometric coefficient in the equilibrium equation.

Solute

The substance present in smaller amount in a solution.

Solution

A homogeneous mixture of two or more substances.

Solvent

The substance present in larger amount in a solution.

Sovation

The process in which an ion or a molecule is surrounded by solvent molecules arranged in a specific manner.

Space-Filling Model

A three-dimensional model based on atomic radii that shows both the orientation and space occupied by the atoms in a molecule.

Specific Heat

The amount of heat energy required to raise the temperature of one gram of the substance by one degree Celsius.

Spectator Ions

Ions that are not involved in the overall reaction.

Spectrochemical Series

A list of ligands arranged in increasing order of their abilities to split the d-orbital energy levels.

Standard Atmospheric Pressure

(1 atm) - The pressure that supports a column of mercury exactly 76 cm high at 0°C at sea level.

Standard emf

The sum of the standard reduction potential of the substance that undergoes reduction and the oxidation potential of the substance that undergoes oxidation.

Standard Enthalpy of Formation

(DH_f°) - The heat change that results when one mole of a compound is formed from its elements in their standard states.

Standard Enthalpy of Reaction

The enthalpy change when the reaction is carried out under standard-state conditions.

Standard Entropy

The absolute entropy at 1 atm and 25°C.

Standard Free-Energy of Formation

(DG_f°) - The free-energy change when 1 mole of a compound is synthesized from its elements in their standard states.

Standard Molar Entropy

The entropy of 1 mol of a substance in its standard state.

Standard Oxidation Potential

The voltage measured as oxidation occurs at the electrode when all solutes are 1 M and all gases are at 1 atm.

Standard Reduction Potential

The voltage measured as a reduction reaction occurs at the electrode when all solutes are 1 M and all gases are at 1 atm.

Standard Solution

A solution of accurately known concentration.

Standard State

The condition of 1 atm of pressure.

Standard Temperature and Pressure

(STP) - 0°C and 1 atm.

State Function

A property that is determined by the state of the system.

State of a System

The values of all pertinent macroscopic variables (for example, composition, volume, pressure, and temperature) of a system.

Stereigenic

See chiral.

Stereoisomers

Compounds that are made up of the same types and numbers of atoms bonded together in the same sequence but with different spatial arrangements.

Stick Model

A graphical representation for a molecule that uses straight lines (or sticks) to represent bonds. In a stick model, atoms are assumed to exist at the intersections of the lines.

Stoichiometric Amounts

The exact molar amounts of reactants and products that appear in the balanced chemical equation.

Stoichiometry

The quantitative study of reactants and products in a chemical reaction.

Stratosphere

The region of the atmosphere extending upward from the troposphere to about 50 km from Earth.

Strong Acid

Strong electrolytes which are assumed to ionize completely in water.

Strong Bases

Strong electrolytes which are assumed to ionize completely in water.

Strong Electrolyte

Completely dissociates, or separates, in water.

Structural Formula

A chemical formula that shows how atoms are bonded to one another in a molecule.

Structural Isomers

Molecules that have the same molecular formula but different structures.

Sublimation

The process in which molecules go directly from the solid into the vapor phase.

Substance

A form of matter that has a definite or constant composition (the number and type of basic units present) and distinct properties.

Substitution Reaction

A reaction in which an atom or group of atoms replaces an atom or groups of atoms in another molecule.

Supercooling

Cooling of a liquid below its freezing point without forming the solid.

Supersaturated Solution

A solution that contains more of the solute than is present in a saturated solution.

Surface Tension

The amount of energy required to stretch or increase the surface of a liquid by a unit area.

Surroundings

The rest of the universe outside the system.

Symbol

A one- or two-letter representation of an element.

Synthesis Reaction

A reaction in which two or more substances combine to form a single product.

System

Any specific part of the universe that is of interest to us.