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A substance that can be separated into simpler substances (elements or other compounds) only by chemical reaction.

Heterogeneous Mixture

A mixture that is not uniform in composition; its components are readily distinguished.

Law of Conservation of Mass

Mass can be neither created nor destroyed in an ordinary chemical or physical process.


Anything that takes up space or has mass.


A combination of two or more substances that are not chemically combined.


A substance formed in a chemical reaction.


A substance in the gaseous state that is ordinarily (at room temperature) a liquid or solid.

Absolute Zero

The zero point on the Kelvin temperature scale, equivalent to -273 ˚C; all molecular motion theoretically stops at this temperature.


The ratio of the mass of an object to its volume.

Kelvin Temperature Scale (Kelvins, K)

The temperature scale in which the freezing point of water is 273 Kelvins and the boiling point is 373 Kelvins; 0 Kelvin is absolute zero.

Percent error

[|experimental value- accepted value|/accepted value] x 100.


The reproducibility, under the same conditions, of a measurement.

Quantitative Measurements

A measurement which gives definite, usually numeric results.

Scientific Notation

Expression of number in the form of N x 10n, where N is equal 1or less than 10 and n is an integer.

Significant Figures

All the digits that can be known precisely.

Dimensional Analysis

A technique of problem-solving that uses the units that are part of a measurement to help solve the problem.

Atomic Mass

The weighted average of the masses of the isotopes of an element.

Atomic Mass Unit

A unit of mass equals to one-twelfth the mass of a carbon-12 atom.

Atomic Number

The number of protons in the nucleus of an atom of an element.


Atoms of the same element that have the same atomic number but different atomic masses due to different numbers of neutrons.

Mass Number

The total number of protons and neutrons in the nucleus of an atom.


Any atom or group of atoms with a negative charge.

Formula Unit

The lowest whole-number ratio of ions in ionic compounds; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl2.


A vertical column of elements in the periodic table; the constituent elements of a group have similar chemical and physical properties.


An atom or group of atoms that has a positive or negative charge; cations are ions with positive charges, and anions are ions with a negative charge.

Ionic Compound

A compound composed of positive and negative ions.


One of the classes of elements having properties of both metals and nonmetals.

Molecular Compound

A compound that is composed of molecules.

Molecular Formula

A chemical formula that shows the actual number and kinds of atoms present in a molecule of a compound.

Polyatomic Ion

A tightly bound group of atoms that behave as a unit and carry a charge.

Representative Element

An element that belongs to an A group in the periodic table; they are called representative elements because they illustrate the entire range of chemical properties.

Transition Metal

An element found in one of the B groups in the periodic table.

Avogadro's number

The number of representative particles contained in one mole of a substance; equal to 6.02 x 1023 particles.

Empirical Formula

A formula with the lowest whole-number ratio of elements in a compound; the empirical formula of hydrogen peroxide, H2O2, is HO.

Molar Volume

The volume occupied by one mole of gas at standard temperature and pressure (STP).


(mol) The amount of a substance that contains 6.02 x 1023 representative of that substance; a gram of formula mass of any substance.

Standard Temperature and Pressure (STP)

The conditions under which the volume of a gas is usually measured; standard temperature is 0˚C and standard pressure is 1 atmosphere (atm).

Activity Series of Metals

A table listing metals in order of decreasing activity.

Combustion Reaction

A chemical reaction change in which two or more substances react to form a single new substance; also caked a synthesis reaction.

Net Ionic Equation

An equation for a reaction in solution showing only those particles directly involved in the chemical change.

Limiting Reagent

Any reactant that is used up first in a chemical reaction; it determines the amount of product that can be formed in the reaction.

Percent Yield

The ratio of the actual yield to the theoretical yield for a chemical reaction expressed as a percentage; a measure of the efficiency of a reaction.


A molecular form of an element that exist in two or more different forms in the same physical state; oxygen, O2, and ozone, O3, are allotropes of the element oxygen.

Amorphous Solid

A term used to describe a solid that lacks an ordered internal structure; denotes a random arrangement of atoms.


Substance in which the atoms, ions, or molecules are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice.

Normal Boiling Point

The boiling point of a liquid at the pressure of one atmosphere.

Standard Atmosphere (ATM)

A unit of pressure; it is the pressure required to support 760 mm of mercury in a mercury barometer at 25 C; this is the average atmospheric pressure at sea level.


The conversion of a solid to a gas without passing through the liquid state.

Triple Point

The point on a phase diagram where all here states of a substance are present.

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