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CIC - Chemistry dictionary
Category: Sciences > Chemistry
Date & country: 09/09/2007, CA
Words: 603


Polymer
A large molecule consisting of chains or rings of linked monomer units, usually characterized by high melting and boiling points.

Polymerization
The combination of many small molecules to form large molecules.

Polymorphous
Refers to substances that crystallize in more than one crystalline arrangement.

Polyprotic Acid
An Acid that can form two or more hydronium ions per molecule; often a least one step of ionization is weak.

Positron
A Nuclear particle with the mass of an electron but opposite charge.

Potential Energy
Energy that matter possesses by virtue of its position, condition or composition.

Precipitate
An insoluble solid formed by mixing in solution the constituent ions of a slightly soluble solution.

Primary Standard
A substance of a known high degree of purity that undergoes one invariable reaction with the other reactant of interest.

Primary Voltaic Cells
Voltaic cells that cannot be recharged; no further chemical reaction is possible once the reactants are consumed.

Proton
A subatomic particle having a mass of 1.0073 amu and a charge of +1, found in thew nuclei of atoms.

PseudobinaryIonic Compounds
Compounds that contain more than two elements but are named like binary compounds.

Quantum Mechanics
Mathematical method of treating particles on the basis of quantum theory, which assumes that energy (of small particles) is not infinitely divisible.

Quantum Numbers
Numbers that describe the energies of electrons in atoms; derived from quantum mechanical treatment.

Radiation
High energy particles or rays emitted during the nuclear decay processes.

Radical
An atom or group of atoms that contains one or more unpaired electrons (usually very reactive species)

Radioactive Dating
Method of dating ancient objects by determining the ratio of amounts of mother and daughter nuclides present in an object and relating the ratio to the object?s age via half-life calculations.

Radioactive Tracer
A small amount of radioisotope replacing a nonradioactive isotope of the element in a compound whose path (for example, in the body) or whose decomposition products are to be monitored by detection of radioctivity; also called a radioactive label.

Radioactivity
The spontaneous disintegration of atomic nuclei.

Raoult's Law
The vapor pressure of a solvent in an ideal solution decreases as its mole fraction decreases.

Rate of Reaction
Change in the concentration of a reactant or product per unit time.

Rate-determining Step
The slowest step in a mechanism; the step that determines the overall rate of reaction.

Rate-law Expression
Equation relating the rate of a reaction to the concentrations of the reactants and the specific rate of the constant.

Reactants
Substances consumed in a chemical reaction.

Reaction Quotient
The mass action expression under any set of conditions (not necessarily equlibrium); its magnitude relative to K determines the direction in which the reaction must occur to establish equilibrium.

Reaction Ratio
The relative amounts of reactants and products involved in a reaction; maybe the ratio of moles. millimoles, or masses.

Reaction Stoichiometry
Description of the quantitative relationships among substances as they participate in chemical reactions.

Reducing Agent
The substance that reduces another substance and is oxidized.

Resonance
The concept in which two or more equivalent dot formulas for the same arrangement of atoms (resonance structures) are necessary to describe the bonding in a molecule or ion.

Reverse Osmosis
Forcing solvent molecules to flow through a semipermable membrane from a concentated solution into a dilute solution by the application of greater hydrostatic pressure on concentrated side than the osmotic pressure opposing it.

Reversible Reaction
Reactions that do not go to completion and occur in both the forward and reverse direction.

S Orbital
A spherically symmetrical atomic orbital; one per energy level.

Salt Bridge
A U-shaped tube containing electrolyte, which connects two half-cells of a voltaic cell.

Saponification
Hydrolysis of esters in the presence of strong soluable bases.

Saturated Hydrocarbons
Hydrocarbons that contain only single bonds. They are also called alkanes or paraffin hydrocarbons.

Saturated Solution
Solution in which no more solute will dissolve.

Second Law of Thermodynamics
The universe tends toward a state of greater diorder in spontaneous processes.

Secondary Standard
a solution that has been titrated against a primary standard. A standard solution is a secondary standard.

Secondary Voltaic Cells
Voltaic cells that can be recharged; original reactanats can be regenerated be reversing the direction of the current flow.

Semiconductor
A substance that does not conduct electricity at low temperatures but does so at higher temperatures.

Semipermable Membrane
A thin partition between two solutions through which certain molecules can pass but others cannot.

Shielding Effect
Electrons in filled sets of s , p orbitals between the nucleus and outer shell electrons shield the outer shell electrons somewhat from the effect of protons in the nucleus; also called screening effect.

Sigma Bonds
Bonds resulting from the head-on overlap of atomic orbitals, in which the region of electron sharing is along and (cylindrically) symmetrical to the imaginary line connecting the bonded atoms.

Sigma Orbital
Molecular orbital resulting from head-on overlap of two atomic orbitals.

Silicones
Polymeric organosilicon compounds; contain individual or cross-linked Si-O chains or rings in which some oxygens of SiO4 tetrahedra are replaced by other groups.

Single Bond
Covalent bond resulting from the sharing of two electrons (one pair) between two atoms.

Solubility Product Constant
Equilibrium constant that applies to the dissolution of a slightly soluble compound.

Solubility Product Principle
The solubility product constant expression for a slightly soluble compound is the product of the concentrations of the constituent ions, each raised to the power that corresponds to the number of ions in one formula unit.

Solute
The dispersed (dissolved) phase of a solution.

Solution
Homogeneous mixture of two or more substances.

Solvation
The process by which solvent molecules surround and interact with solute ions or molecules.

Solvent
The dispersing medium of a solution.

Solvolysis
The reaction of a substance with the solvent in which it is dissolved.

Specific Gravity
The ratio of the density of a substance to the density of water.

Specific Heat
The amount of heat required to raise the temperature of one gram of substance one degree Celsius.

Specific Rate Constant
An experimentally determined (proportionality) constant, which is different for different reactions and which changes only with temperature; k in the rate-law expression: Rate = k [A] x [B]v.

Spectator Ions
Ions in a solution that do not participate in a chemical reaction.

Spectral Line
Any of a number of lines corresponding to definite wavelengths of an atomic emission or absorption spectrum; represents the energy difference between two energy levels.

Spectrochemical Series
Arrangement of ligands in order of increasing ligand field strength.

Spectrum
Display of component wavelengths (colours) of electromagnetic radiation.

Square Planar
A term used to describe molecules and polyatomic ions that have one atom in the center and four atoms at the corners of a square.

Square Planar Complex
Complex in which the metal is in the center of a square plane, with ligand donor atoms at each of the four corners

Standard Electrode Potential
By convention , potential, Eo, of a half-reaction as a reduction relative to the standard hydrogen electrode when all species are present at unit activity.

Standard Electrodes
Half-cells in which the oxidized and reduced forms of a species are present at unit activity; 1.0M solutions of dissolved ions, 1.0atm partial pressure of gases, and pure solids and liquids.

Standard Entropy
The absolute entropy of a substance in its standard state at 298 K.

Standard Molar Volume
The volume occupied by one mole of an ideal gas under standard conditions; 22.4liters.

Standard Reaction
A reaction in which the numbers of moles of reactants shown in the balanced equation, all in their standard states, are completely converted to the numbers of moles of products shown in the balanced equation, also sall at their standard state.

Stereoisomers
Isomers that differ only in the way that atoms are oriented in space; consist of geometrical and optical isomers.

Stoichiometry
Description of the quantitative relationships among elements and compounds as they undergo chemical changes.

Strong Electrolyte
A substance that conducts electricity well in a dilute aqueous solution.

Strong Field Ligand
Ligand that exerts a strong crystal or ligand electrical field and generally forms low spin complexes with metal ions when possible.

Structural Isomers
Compounds that contain the same number of the same kinds of atoms in different geometric arrangements.

Sublimation
The direct vaporization of a sold by heating without passing through the liquid state.

Substance
Any kind of matter all specimens of which have the same chemical composition and physical properties.

Substitution Reaction
A reaction in which an atom or a group of atoms is replaced by another atom or group of atoms.

Supercooled Liquids
Liquids that, when cooled, apparently solidify but actually continue to flow very slowly under the influence of gravity.

Supercritical Fluid
A substance at temperature above its critical temperature.

Supersaturated Solution
A solution that contains a higher than saturation concentration of solute; slight disturbance or seeding causes crystallization of excess solute.

Suspension
A heterogeneous mixture in which solute-like particles settle out of solvent-like phase some time after their introduction.

Temperature
A measure of the intensity of heat, i.e. the hotness or coldness of a sample. or object.

Ternary Acid
A ternary compound containing H, O, and another element, often a nonmetal.

Ternary Compound
A compound consisting of three elements; may be ionic or covalent.

Tetrahedral
A term used to describe molecules and polyatomic ions that have one atom in center and four atoms at the corners of a tetrahedron.

Theoretical Yield
Maximum amount of a specified product that could be obtained from specified amounts of reactants, assuming complete consumption of limiting reactant according to only one reaction and complete recovery of product. (Compare with Actual Yield)

Thermal Cracking
Decomposition by heating a substance in the presence of a catalyst and in the absence of air.

Thermodynamics
The study of the energy transfers accompanying physical and chemical processes.

Thermonuclear Energy
Energy from nuclear fusion reactions.

Third Law of Thermodynamics
The entropy of a hypothetical pure, perfect, crystalline sustance at absolute zero temperature is zero.

Titration
A Procedure in which one solution is added to another solution until the chemical reaction between the two solutes is complete; the concentration of one solution is known and that of the other is unknown.

Total Ionic Equation
Equation for a chemical reaction written to show the predominant form of all species in aqueous solution or in contact with water.

Transition State Theory
Theory of reaction rates that states that reactants pass through high-energy transition states before forming products.

Tyndall Effect
The scattering of light by colloidal particles.

Unsaturated Hydrocarbons
Hydrocarbons that contain double or triple carbon-carbon bonds.

Valence Bond Theory
Assumes that covalent bonds are formed when atomic orbitals on different atoms overlap and the electrons are shared.

Valence Electrons
Outermost electrons of atoms; usually those involved in bonding.

van der Waals' Equation
An equation of state that extends the ideal gas law to real gases by inclusion of two empirically determined parameters, which are different for different gases.

Vapor
A gas formed by boiling or evaporating a liquid.

Vapor Pressure
The particle pressure of a vapor at the surface of its parent liquid.

Voltage
Potential difference between two electrodes; a measure of the chemical potential for a redox reaction to occur.

Voltaic Cells
Electrochemical cells in which spontaneous chemical reactions produce electricity; also called galvanic cells.

Water Equivalent
The amount of water that would absorb the same amount of heat as the calorimeter per degree temperature increase.