1. The central core of the atom, containing protons and usually neutrons NUCLEUS

PROTON Small positively charged particles that are found in the nucleus of an atom

NEUTRON Small uncharged particles that are found in the nucleus of an atom

ELECTRON Tiny, negatively charged, high-energy particles that move around outside the nucleus of an atom

VALENCE ELECTRONS The electrons that are farthest away from the nucleus of an atom and are involved in chemical interactions.

ELECTRON DOT DIAGRAM A representation of the number of valence electrons in an atom, using dots placed around the symbol of an element

ATOMIC NUMBER The number of protons in the nucleus of an atom

GROUP Elements in the same vertical column of the periodic table. Also called family.

PERIOD Elements in the same horizontal row of the periodic table.

HALOGEN REACTIVE NON METAL An element belonging to Group 17 of the periodic table.

ION An atom or group of atoms that has become electrically charged.

IONIC BOND The attraction between oppositely charged ions.

POLYATOMIC ION An ion that is made of more than one atom.

CRYSTAL An orderly, three-dimensional pattern of ions or atoms in a solid.

MINERAL A naturally occurring solid that has a crystal structure and a definite chemical composition.