Chemistry Glossary

acid a compound that yields H+ ions in solution or a solution in which the concentration of H+ exceeding OH-.

acid ionization constant the equilibrium constant describing the degree of ionization of an acid.

actinides the row of elements below the periodic table, from thorium to lawrencium.

alkali synonym for base.

alkali metals the column of elements from lithium to francium.

alkaline earths the column of elements from beryllium to radium.

alkane a hydrocarbon without a double bond, triple bond, or ring structure.

alkene a hydrocarbon with one or more double bonds and no triple bond.

alkyne a hydrocarbon with one or more triple bonds.

alpha particle a cluster of 2 protons and 2 neutrons emitted from a nucleus in one type of radioactivity.

anion a chemical species with a negative charge.

anode the negative electrode at which oxidation occurs.

aqueous refers to a solution with water as solvent.

aromatic refers to an organic compound with a benzene-like ring.

atom the smallest amount of an element; a nucleus surrounded by electrons.

atomic number the number of protons in the nucleus of the chemical element.

atomic weight the weight in grams of one mole of the chemical element; approximately the number of protons and neutrons in the nucleus.

Avogadro's law equal volumes of gases at the same temperature and pressure that contain the same number of molecules.

Avogadro's number 6.02 x 1023, the number of molecules in 1 mole of a substance.

base a compound that yields OH- ions in solution or a solution in which the concentration of OH- exceeds H+.

beta particle an electron emitted from a nucleus in one type of radioactivity.

boiling point the temperature at which a liquid changes to a gas.

boiling point elevation an increase in the boiling point of a solution, proportional to the concentration of solute particles.

Boyle's law the volume of a gas varies inversely with pressure.

calorie a unit of energy, equal to 4.184 joules.

catalyst a substance that accelerates a chemical reaction without itself being consumed.

cathode the electrode at which reduction occurs.

cation an atom or molecule with a positive charge.

Charles' law the volume of a gas varies directly with absolute temperature.

chemical equation a shorthand way of describing a chemical change using symbols of elements and formulas of compounds.

chemical formula a representation of a compound to show its composition using symbols and subscript numbers.

compound a substance formed by the chemical combination of two or more elements.

concentration the relative abundance of a solute in a solution.

congeners elements with similar properties, arranged in columns of the periodic table.

conjugate an acid and base that are related by removing or adding a single hydrogen ion.

covalent bond atoms linked together by sharing valence electrons.

critical point a point in a phase diagram where the liquid and gas states cease to be distinct.

crystalline the regular, geometric arrangement of atoms in a solid.

decomposition a chemical reaction in which a compound is broken down into simpler compounds or elements.

dissociation the separation of a solute into constituent ions.

electrochemical cell a device that uses a chemical reaction to produce an electric current.

electrode the point in an electrochemical cell at which reduction or oxidation occurs.

electrolysis the decomposition of a substance by an electric current.

electrolyte a substance that forms ions when dissolved in water.

electromotive force the electrical potential produced by a chemical reaction voltage.

electron a light subatomic particle with negative charge; found in orbitals surrounding an atomic nucleus.

electronegativity a number describing the attraction of an element for electrons in a chemical bond.

element a substance that cannot be decomposed; each chemical element is characterized by the number of protons in the nucleus.

EMF See electromotive force.

endothermic refers to a reaction that requires heat.

energy the concept of motion or heat required to do work.

enthalpy the thermodynamic quantity measuring the heat of a substance.

entropy the thermodynamic quantity measuring the disorder of a substance.

equilibrium a balanced condition resulting from two opposing reactions.

equilibrium constant the ratio of concentrations of products to reactants for a reaction at chemical equilibrium.

exothermic refers to a reaction that releases heat.

faraday a unit of electric charge equal to that on 1 mole of electrons.

Faraday's laws two laws of electrolysis relating the amount of substance to the quantity of electric charge.

fluid a liquid or gas.

free energy the thermodynamic quantity measuring the tendency of a reaction to proceed; also called Gibbs free energy.

freezing point the temperature at which a liquid changes to a solid.

freezing point depression the decrease in freezing point of a solution, proportional to the concentration of solute particles.

fusion melting.

gas a state of matter in which molecules are widely separated, fluid, expandable, and compressible.

gas constant R equals 0.082 liter-atmospheres per mole-degree.

gram formula weight an amount of a substance equal in grams to the sum of the atomic weights.

ground state the electronic configuration of lowest energy for an atom.

group a column of elements in the periodic table.

half-reaction an oxidation or reduction reaction with free electrons as a product or reactant.

halogens the column of elements from fluorine to astatine.

heat a form of energy that spontaneously flows from a warm body to a cold body.

heat capacity the amount of energy needed to raise the temperature of a substance by one degree Celsius.

hydrocarbon an organic compound containing only carbon and hydrogen.

hydrogen bond a weak, secondary bond between a partially positive hydrogen atom and a partially negative N, O, or F atom. An inter-molecular force of attraction.

hydroxide refers to the OH- ion.

ideal gas equation the equation relating the volume of a gas to its pressure, temperature and moles of gas.

inert gases the column of elements from helium to radon; also called noble gases.

ion an atom with an electric charge due to gain or loss of electrons.

ionic bond atoms linked together by the attraction of unlike charges.

ionization adding or subtracting electrons from an atom; alternatively, the dissociation of a solute into ions.

isoelectronic refers to several dissimilar atoms or ions with identical electronic configurations.

isomers several molecules with the same composition but different structures.

isotope a variety of an element characterized by a specific number of neutrons in the nucleus.

joule a unit of energy equal to 0.239 calorie.

lanthanides the row of elements beneath the periodic table, from cerium to lutetium; also called rare earths.

Le Chatelier's principle a system that in equilibrium is disturbed adjusts so as to minimize the disturbance.

liquid a state of matter in which the molecules are touching, fluid, incompressible.

litmus an indicator that turns red in acid and blue in alkaline solution.

melting point the temperature at which a solid changes to a liquid.

metallic bond atoms linked together by the migration of electrons from atom to atom.

metals the elements in the middle and left parts of the periodic table, except for hydrogen.

molality the number of moles of solute in 1 kilogram of solvent.

molarity the number of moles of solute in 1 liter of solution.

molar heat capacity the amount of heat required to raise the temperature of 1 mole of substance 1 degree Celsius.

mole an amount of a substance equal in grams to the sum of the atomic weights.

mole fraction the fraction of moles (or molecules) of one substance in the total moles (or molecules) of all substances in the mixture. If the mole fraction of substance A is 0.1, one-tenth of all the molecules in a mixture are A molecules.

molecular formula describes the ratio of elements in a molecule.

molecule a group of atoms linked together by covalent bonds.

neutralization the chemical reaction of an acid and base to yield a salt and water.

neutron a heavy subatomic particle with zero charge; found in an atomic nucleus.

noble gases the column of elements from helium to radon; also called inert gases.

nonmetals the elements in the upper right part of the periodic table, and also hydrogen.

nucleon a proton or neutron found in an atomic nucleus.

nucleus the core of an atom, containing protons and neutrons.

orbital a component of a subshell occupied by up to 2 electrons.

organic refers to compounds based on carbon.

organic chemistry an area of chemistry dealing principally with the chemistry of carbon.

oxidation the loss of electrons by a species.

oxidation number a signed integer representing the real or hypothetical charge on an atom.

oxide a compound of oxygen and another element.

period a horizontal row of elements in the periodic table.

periodic table display of the elements in order of atomic number with similar elements falling into columns.

pH a number describing the concentration of hydrogen ions in a solution. Equals -log[H+].

phase a substance with uniform composition and definite physical state.

polar bond a bond with both ionic and covalent characteristics.

polyprotic refers to an acid with several hydrogens that can ionize.

precipitate a solid that separates from solution.

product a substance on the right side of a chemical reaction.

proton a heavy subatomic particle with a positive charge; found in an atomic nucleus.

radioactivity the emission of subatomic particles from a nucleus.

rare earths the elements from cerium to lutetium; lanthanides.

reactant a substance on the left side of a chemical reaction.

redox refers to a reaction in which simultaneous reduction and oxidation occur.

reduction the gain of electrons by a species.

salt a solid compound composed of both metallic and nonmetallic elements, often as ions.

saturated describes a solution that holds as much solute as possible.

shell a set of electron orbitals with the same principal quantum number.

solid a state of matter in which the molecules are touching and possessing rigid shape and is not compressible.

solubility the upper limit of concentration of a solute.

solubility product the constant obtained by multiplying the ion concentrations in a saturated solution.

solute the substance that is dissolved in a solution.

solution a homogeneous mixture consisting of a solvent and one or more solutes.

solvent the host substance of dominant abundance in a solution.

specific heat capacity the amount of heat required to raise 1 gram of a substance 1 degree Celsius.

standard temperature and pressure 0° and 1 atmosphere.

states of matter solid, liquid, and gas.

stoichiometric refers to compounds or reactions in which the components are in fixed, whole-number ratios.

STP See standard temperature and pressure.

strong electrolyte an acid, base, or salt that dissociates almost completely to ions in aqueous solution.

structural formula depicts the bonding of atoms in a molecule.

sublimation the transformation of a solid directly to a gas without an intervening liquid state.

subshell a set of electron orbitals with the same principal and second quantum number; for example, 2p, 3s, and so on.

symbol an abbreviation for the name of an element; for example, C for carbon.

transition metals the three rows of elements in the middle of the periodic table, from scandium to mercury.

triple point a point in a phase diagram where the three states of matter are in equilibrium.

valence a signed integer describing the combining power of an atom.

valence electrons the outermost shell of electrons in an atom or ion.

weak electrolyte an acid, base, or salt that dissociates only slightly to form ions in solution.