Chemical Equation A method or model for describing what happens to reactants and products during a chemical reaction, using chemical formulas of the chemicals involved.

Periodic Table A graphic arrangement that organizes elements into rows and columns on the basis of their atomic numbers; the resulting arrangement displays patterns and relationships among the elements.

Periods Horizontal rows in the periodic table.

Groups Vertical columns in the periodic table.

Shells Regions around the nucleus of an atom that may be occupied by electrons.

Valence Shell The outer electron shell of an atom.

Valence Electrons One or more electrons occupying the outer electron shell of an atom.

Ion An atom or group of atoms that carries an electrical charge; positively charged ions are called cations and negatively charged ions are called anions.

Cation A positively charged ion that results when a neutral atom gives up an electron.

Anion A negatively charged ion that results when a neutral atom gains an electron.

Electron Dot Diagram A model that represents an atom and its valence electrons by substituting an element’s symbol for its nucleus and inner-shell electrons, and placing dots around the symbol to show the number of valence electrons.

Ionic Compounds A substance that is composed of cations and anions.

Ionic Bond The force of attraction between the oppositely charged ions in an ionic compound.

Covalent Bond The force of attraction between atoms that share one, two, or three pairs of electrons.

Molecule A neutral particle that is made up of two or more atoms that are joined together by covalent bonds.

Molecular Compound A substance that is composed of molecules.

Diatomic Molecules A molecule that contains two identical atoms.

Electrolyte A substance that dissolves in water, producing a solution that is able to conduct electricity.

Binary Compound A compound such as water and sodium chloride that contains two different elements.

Polyatomic Ions An ion that consists of two or more different non-metal atoms that are joined by covalent bonds.

Reactants The substance(s) that undergoes a chemical change in a chemical reaction.

Products The substance(s) that results from a chemical change in a chemical reaction.