7. Isotopes:Isotopes: atoms with the same number of protons but a different number of neutrons. –carbon-12 has 6 protons and 6 neutrons; –carbon-13 has 6 protons and 7 neutrons; –carbon-14 has 6 protons and 8 neutrons; Most elements found on Earth are mixtures of isotopes: –chlorine is 75.77% chlorine-35 (18 neutrons) and 24.23% chlorine-37 (20 neutrons).

8. Mass number:Mass number: the number of protons and neutrons in the nucleus of an atom. –the mass of the electrons in an atom is so small compared to that of its protons and neutrons that electrons are not counted in determining mass number. Atomic number:Atomic number: the number of protons in the nucleus of an atom. a carbon atom of this composition is referred to as carbon-12.

9. Atomic weight:Atomic weight: the weighted average of the masses (in amu) of the naturally occurring isotopes of an element. –example: chlorine is 75.77% chlorine-35 and 24.23% chlorine-37

10. EOC

32. Empirical Formula Molecular Formula is…