Chemistry Dictionary Terminology "Z"

Chemistry Dictionary

Terminology "Z"

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Zone Refining

A method of purifying a bar of metal by passing it through an induction heater; this causes impurties to move along a melted portion.

Chemistry Dictionary Terminology "W"

Chemistry Dictionary

Terminology "W"

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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.

Chemistry Dictionary Terminology "V"

Chemistry Dictionary

Terminology "V"

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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.

Valence Shell Electron Pair Repulsion Theory

Assumes that electron pairs are arranged around the central element of a molecule or polyatomic ion so that there is maximum separation (and minimum repulsion) among regions of high electron density.

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.

Chemistry Dictionary Terminology "U"

Chemistry Dictionary

Terminology "U"

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Unsaturated Hydrocarbons

Hydrocarbons that contain double or triple carbon-carbon bonds.

Chemistry Dictionary Terminology "T"

Chemistry Dictionary

Terminology "T"

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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.

Chemistry Dictionary Terminology "S"

Chemistry Dictionary

Terminology "S"

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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.

S Orbital

A spherically symmetrical atomic orbital; one per energy level.

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 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 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 Entropy

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

Standard Molar Enthalphy of Formation

The amount of heat absorbed in the formation of one mole of a substance in a specified state from its elements in their standard states.

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.

Chemistry Dictionary Terminology "R"

Chemistry Dictionary

Terminology "R"

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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-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.

Rate of Reaction

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

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.

Chemistry Dictionary Terminology "Q"

Chemistry Dictionary

Terminology "Q"

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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.

Chemistry Dictionary Terminology "P"

Chemistry Dictionary

Terminology "P"

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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.

Percentage Ionization

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

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.

Period

The elements in a horizontal row of the periodic table.

Periodicity

Regular periodic variations of properties of elements with atomic number (and position in 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.

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.

Polymerization

The combination of many small molecules to form large molecules.

Polymer

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

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.

Chemistry Dictionary Terminology "O"

Chemistry Dictionary

Terminology "O"

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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.

Chemistry Dictionary Terminology "N"

Chemistry Dictionary

Terminology "N"

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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.

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

Nitrogen Cycle

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

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.

Nuclides

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

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.