Science Course: Chemistry Definitions


Periodic Table: a graphic arrangement that organizes elements into rows and columns on the basis of their atomic numbers

Periods: horizontal rows in the periodic table, which contain the same number of energy levels or shells

Groups: vertical columns in the periodic table, which contain the same number of electrons in the outermost shells

Element:a substance with only one kind of atom

††††††††††† Example: H, He, Be, B

Atom: smallest part of an element that has the characteristics of that element

Shells: regions around the nucleus of an atom that may be occupied by electrons

Valence Shell: the outermost energy level of an atom

Valence Electron: one or more of the electrons occupying the outermost energy level of an atom.

Neils-Bohr Diagram:picture of the energy levels of an atom, showing the electrons in each shell

Electron Dot Diagram:a model that represents an atom and its valence electrons, by substituting an elementís symbol for its nucleus and outermost shell electrons, shown as dots

Compound: substance composed of two or more different elements, chemically combined

††††††††† Example: water H2O

Ion: an atom or group of atoms that carries an electric charge

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

Ionic Compound: substance that is composed of cations and anions forming ionic bonds

Ionic Bond:the force of attraction between the oppositely charged ions ofan ionic compound

Electrolyte: substance which dissolves in water, producing a solution that is able to conduct electricity

Molecular Compound: substance composed of molecules joined by covalent bonds

Molecule: neutral particle made up of two or more atoms that are joined together by covalent bonds††† Example: water H2O

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

Metalloid: solid at room temperature, which can be shiny or dull, may conduct electricity, poor conductor of heat, and is brittle††† It has the characteristics of a metal and non-metal.