Important Terms
• ATOM - Smallest unit of an element that keeps its chemical properties
• ELEMENT – Unique substance with the same number of protons in
every atom, that cannot be broken down by chemical means
• MOLECULE - Smallest unit of a compound that keeps its chemical
properties (made of two or more atoms)
• COMPOUND - Substance that can be broken into separate elements by
chemical reactions
• ELECTRON (e-) - Particle moving around the nucleus of an atom with a
negative charge; it does NOT have a definitive position in the energy
level; (mass = 1/2000 amu)
• NEUTRON (N) - Particle in the nucleus of an atom with no charge;
(mass = 1 amu)
• PROTON (P) - Particle in the nucleus of an atom with a positive charge;
(mass = 1 amu)
• ION - Electrically charged atom (i.e., excess positive or negative charge)
• NUCLEUS - Dense, central core of an atom, does not have a definitive
membrane
• ATOMIC MASS – total mass of the protons and neutrons in an atom
• ISOTOPES - atoms of an element each form having a different atomic
mass. Isotopes of an element have the same number of protons but
different numbers of neutrons – which ultimately alters the mass