1. TOPIC 1 vocabulary

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

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

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

5. ATOMIC NUMBER Number of protons in the nucleus of an atom

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

7. ELECTRON Fundamental particle of matter having a negative charge

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

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

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

11. HETEROGENEOUS Mixture in which substances are not uniformly distributed

12. HOMOGENEOUS Mixture in which substances are uniformly distributed

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

14. MASS NUMBER protons + neutrons

15. MIXTURE Two or more substances not chemically combined

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

17. NUCLEUS Dense, positively charged, central core of an atom

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

19. PROTON Positively charged particle in the nucleus of an atom

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

21. VALENCE Outermost energy level around an atom

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