TOPIC 1 vocabulary

ATOM Smallest part of an element that can enter into a chemical reaction

ATOMIC MASS Average mass of all the isotopes of a sample of an element

ATOMIC MASS UNIT 1/12 the mass of a carbon-12 atom

ATOMIC NUMBER Number of protons in the nucleus of an atom

COMPOUND Two or more elements chemically combined in definite proportion by mass

ELECTRON Fundamental particle of matter having a negative charge

ELEMENT Substance that cannot be broken down or decomposed into a simpler substance by chemical means

EXCITED STATE Condition that exists when electrons of an atom occupy higher energy levels, leaving lower energy level(s) vacant

GROUND STATE Condition of an atom or ion in which electrons occupy the lowest possible energy levels

HETEROGENEOUS Mixture in which substances are not uniformly distributed

HOMOGENEOUS Mixture in which substances are uniformly distributed

ISOTOPE Atom of an element with a specific (sometimes unusual) number of neutrons with the protons

MASS NUMBER protons + neutrons

MIXTURE Two or more substances not chemically combined

NEUTRON Particle in the nucleus of an atom with no charge (neutral)

NUCLEUS Dense, positively charged, central core of an atom

ORBITAL Region in an atom (outside the nucleus) where an electron with a specific amount of energy is most likely to be located

PROTON Positively charged particle in the nucleus of an atom

PURE SUBSTANCE Material with the same composition throughout; an element or compound

VALENCE Outermost energy level around an atom

WAVE-MECHANICAL MODEL Current model of the atom in which electrons exist in orbitals of various shapes and pathways, called the electron cloud