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


Mass Deficiency
The amount of matter that would be converted into energy if an atom were formed from constituent particles.

Mass Number
The sum of the numbers of protons and neutrons in an atom; an integer.

Mass Spectrometer
An instrument that measures the charge-to-mass ratio of charged particles. For further information see Mass Spectrometry

Matter
Anything that has mass and occupies space.

Mechanism
The sequence of steps by which reactants are converted into products.

Melting Point
The temperature at which liquid and solid coexist in equilibrium; also the freezing point.

Meniscus
The shape assumed by the surface of a liquid in a cylindrical container.

Metal
An element below and to the left of the stepwise division (metalloids) in the upper right corner of the periodic table; about 80% of the known elements are metals.

Metallic Bonding
Bonding within metals due to the electrical attraction of positively charges metal ions for mobile electrons that belong to the crystal as a whole.

Metallic Conduction
Conduction of electrical current through a metal or along a metallic surface.

Metalloids
Elements with properties intermediate between metals and nonmetals: B, Al, Si, Ge, As, Sb, Te, Po, and At.

Metallurgy
Refers to the overall processes by which metals are extracted from ores.

Metathesis Reactions
Reactions in which two compounds react to form two new compounds, with no changes in oxidation number. Reactions in which the ions of two compounds exchange partners.

Method of Initial Rates
Method of determining the rate-law expression by carrying out a reaction with different initial concentrations and analyzing the resultant changes in initial rates.

Miscibility
The ability of one liquid to mix with (dissolve in) another liquid.

Mixture
A sample of matter composed of two or more substances, each of which retains its identity and properties.

Moderator
A substance such as hydrogen, deuterium, oxygen or paraffin capable of slowing fast nuetrons upon collision.

Molality
Concentration expressed as number of moles of solute per kilogram of solvent.

Molar Solubility
Number of moles of a solute that dissolve to produce a litre of saturated solution.

Molarity
Number of moles of solute per litre of solution.

Mole Fraction
The number of moles of a component of a mixture divided by the total number of moles in the mixture.

Molecular Equation
Equation for a chemical reaction in which all formulas are written as if all substances existed as molecules; only complete formulas are used.

Molecular Formula
Formula that indicates the actual number of atoms present in a molecule of a molecular substance.

Molecular Geometry
The arrangement of atoms (not lone pairs of electrons) around a central atom of a molecule or polyatomic ion.

Molecular Orbital
An orbit resulting from overlap and mixing of atomic orbitals on different atoms. An MO belongs to the molecule as a whole.

Molecular Orbital Theory
A theory of chemical bonding based upon the postulated existence of molecular orbitals.

Molecular Weight
The mass of one molecule of a nonionic substance in atomic mass units.

Molecule
The smallest particle of an element or compound capable of a stable, independent existence.

Monoprotic Acid
Acid that can form only one hydronium ion per molecule; may be strong or weak. Acid that contains one ionizable hydrogen atom per formula unit.

Mother Nuclide
Nuclide that undergoes nuclear decay.

Native State
Refers to the occurrence of an element in an uncombined or free state in nature.

Natural Radioactivity
Spontaneous decomposition of an atom.

Nernst Equation
Corrects standard electrode potentials for nonstandard conditions.

Net Ionic Equation
Equation that results from canceling spectator ions and eliminating brackets from a total ionic equation.

Neutralization
The reaction of an acid with a base to form a salt and water. Usually, the reaction of hydrogen ions with hydrogen ions to form water molecules.

Neutron
A neutral subatomic particle having a mass of 1.0087 amu.

Nickel-cadmium cell (Nicad battery)
A dry cell in which the anode is Cd, the cathode is NiO2, and the electrolyte is basic.

Nitrogen Cycle
The complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere and hydrosphere.

Nitrogenases
A class of enzymes found in bacteria within root nodules in some plants, which catalyze reactions by which N2 molecules from the air are converted to ammonia. For more information see Enzymes

Noble Gases (Rare Gases)
Elements of the periodic Group 0; also called rare gases; formerly called inert gases, He,Ne,Ar, Kr, Xe, Rn.

Nodal Plane
A region in which the probability of finding an electron is zero.

Nonbonding Orbital
A molecular orbital derived only from an atomic orbital of one atom; lends neither stability nor instability to a molecule or ion when populated with electrons.

Nonelectrolyte
A substance whose aqueous solutions do not conduct electricity.

Nonpolar Bond
Covalent bond in which electron density is symmetrically distributed

Nuclear Binding Energy
Energy equivalent of the mass deficiency; energy released in the formation of an atom from the subatomic particles.

Nuclear Fission
The process in which a heavy nucleus splits into nuclei of intermediate masses and one or more protons are emitted.

Nuclear Reaction
Involves a change in the composition of a nucleus and can evolve or absorb an extraordinarily large amount of energy

Nuclear Reactor
A system in which controlled nuclear fisson reactions generate heat energy on a large scale, which is subsequently converted into electrical energy.

Nucleons
Particles comprising the nucleus; protons and neutrons.

Nucleus
The very small, very dense, positively charged center of an atom containing protons and neutrons, as well as other subatomic particles.

Nuclide Symbol
Symbol for an atom A/Z E, in which E is the symbol of an element, Z is its atomic number, and A is its mass number.

Nuclides
Refers to different atomic forms of all elements in contrast to ?isotopes?, which refer only to different atomic forms of a single element.

Octahedral
A term used to describe molecules and polyatomic ions that have one atom in the center and six atoms at the corners of a octahedron.

Octane Number
A number that indicates how smoothly a gasoline burns.

Octet Rule
Many representative elements attain at least a share of eight electrons in their valence shells when they form molecular or ionic compounds; there are some limitations.

Oil
Liquid triester of glycerol and unsaturated fatty acids.

Open Sextet
Refers to species that have only six electrons in the highest energy level of the central element (many Lewis acids).

Optical Activity
The rotation of plane polarized light by one of a pair of optical isomers.

Optical Isomers
Stereoisomers that differ only by being nonsuperimposable mirror images of each other, like right and left hands, also called enantiomers.

Ore
A natural deposit containing a mineral of an element to be extracted.

Organic Chemistry
The chemistry of substances that contain carbon-hydrogen bonds.

Osmosis
The process by which solvent molecules pass through a semipermable membrane from a dilute solution into a more concentrated solution.

Osmotic Pressure
The hydrostatic pressure produced on the surface of a semipermable membrane by osmosis.

Ostwald Process
A process for the industrial production of nitrogen oxide and nitric acid from ammonia and oxygen.

Outer Orbital Complex
Valence bond designation for a complex in which the metal ion utilizes d orbitals in the outermost (occupied) shell in hybridization.

Overlap
The interaction of orbitals on different atoms in the same region of space.

Oxidation
An algebraic increase in the oxidation number; may correspond to a loss of electrons.

Oxidation Numbers
Arbitrary numbers that can be used as mechanical aids in writing formulas and balancing equations; for single- atom ions they correspond to the charge on the ion; more electronegative atoms are assigned negative oxidation numbers (also called Oxidation states).

Oxidation-reduction Reactions
Reactions in which oxidation and reduction occur; also called redox reactions.

Oxide
A binary compound of oxygen.

Oxidizing Agent
The substance that oxidizes another substance and is reduced.

Pairing
A favourable interaction of two electrons with opposite m , values in the same orbital.

Pairing Energy
Energy required to pair two electrons in the same orbital.

Paramagnetism
Attraction toward a magnetic field, stronger than diamagnetism, but still weak compared to ferromagnetism.

Partial Pressure
The pressure exerted by one gas in a mixture of gases.

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).

Peroxide
A compound containing oxygen in the -1 oxidation state. Metal peroxides contain the peroxide ion, O22-

pH
Negative logarithm of the concentration (mol/L) of the H3O+[H+] ion; scale is commonly used over a range 0 to 14.

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.

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

Photochemical Smog
A brownish smog occurring in urban areas receiving large amounts of sunlight; caused by photochemical (light-induced) reactions among nitrogen oxides, hydrocarbons and other components of polluted air that produce photochemical oxidants.

Photoelectric Effect
Emission of an electron from the surface of a metal caused by impinging electromagnetic radiation of certain minimum energy; current increases with increasing intensity of radiation.

Photon
A packet of light or electromagnetic radiation; also called quantum of light

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.

Polarization
The buildup of a product of oxidation or a reduction of an electrode, preventing further reaction.

Polydentate
Refers to ligands with more than one donor atom.

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