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AllChemicals.info - Chemical glossary
Category: Sciences > Chemical
Date & country: 10/12/2007, UK
Words: 391


Particulate Matter
Fine divided solid particles suspended in polluted air.

Pauli Exclusion Principle
No two electrons in the same atom may have identical sets of four quantum numbers.

Percent by Mass
100% times the actual yield divided by theoretical yield.

Percent Composition
The mass percent of each element in a compound.

Percent Purity
The percent of a specified compound or element in an impure sample.

Percentage Ionization
The percentage of the weak electrolyte that ionizes in a solution of given concentration.

Period
The elements in a horizontal row of the periodic table.

Periodic Law
The properties of the elements are periodic functions of their atomic numbers.

Periodic Table
An arrangement of elements in order of increasing atomic numbers that also emphasizes periodicity.

Periodicity
Regular periodic variations of properties of elements with atomic number (and position in the periodic table).

Phase Diagram
Diagram that shows equilibrium temperature-pressure relationships for different phases of a substance.

Phenol
Hydrocarbon derivative containing an [OH] group bound to an aromatic raing.

Phosphorus Oxychloride
Colorless to slightly yellow fuming liquid.Mol. Wt.: 153.39M.P.: 20CB.P.: 105.1CDensity: 1.685 @ 15.5CVapor Pressure: 40 mm @ 27.3CVapor Density: 5.3Used as the phosphorus source for phosphorus diffusion.

Photochemical Oxidants
Photochemically produced oxidizing agents capable of causing damage to plants and animals.

Physical Change
A change in which a substance changes from one physical state to another but no substances with different composition are formed. Example Gas to Liquid - Solid.

Plasma
A physical state of matter which exists at extremely high temperatures in which all molecules are dissociated and most atoms are ionized.

Polar Bond
Covalent bond in which there is an unsymmetrical distribution of electron density.

Polarimeter
A device used to measure optical activity.

Polydentate
Refers to ligands with more than one donor atom.

Polyene
A compound that contains more than one double bond per molecule.

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

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

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

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.

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

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.

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-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 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.

Saccharic
of or derived from saccharin or a saccharine substance.

Saccharide
an organic compound containing a sugar or sugars.

Salicylate
a salt or ester of salicylic acid.

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.

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.

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

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.

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.

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

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.

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

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.

Supercritical Fluid
A substance at temperature above its critical temperature.

Surface Tension
It is the force in dynes acting along the surface of the liquid 1cm in length and perpendicular to it.

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

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.

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.

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.

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.

Viscosity
Resistance offered by the molecules of a liquid to flow is termed as viscosity.

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

Weak Electrolyte
A substance that conducts electricity poorly in a dilute aqueous solution.

Weak Field Ligand
A Ligand that exerts a weak crystal or ligand field and ge- nerally forms high spin complexes with metals.

xanthate
a salt or ester of xanthic acid.

xanthene dye
any of a group of dyes having a molecular structure related to that of xanthene in which the aromatic (C6H4) groups are the chromophore.

xylan
the pentosan occurring in woody tissue that hydrolyzes to xylose: used as a source of furfural.