| A | B |
|---|
| atomic mass unit | defined as the mass of a carbon -12 atom |
| nucleus | central core of an atom, which contains most of the atom's mass |
| group | a vertical column of elements in the periodic table |
| neutrons | subatomic particles with no charge |
| protons | positively charged subatomic particles |
| atom | the smallest particle of an element that retains its identity in a chemical reaction |
| atomic number | the number of protons in the nucleus of an element |
| electrons | negatively charged subatomic particles |
| isotopes | atoms with the same number of protons but different numbers of neutrons |
| periodic table | an arrangement of elements according to similarities in their properties |
| atomic mass | the weighted average mass of the atoms in a naturally a naturally occuring sample of the element |
| mass number | the total number of protons and neutrons in an atom |
| Dalton’s atomic theory | used scientific evidence to back Democritus’ theory listing four statements about atoms/elements |
| period | horizontal rows in the periodic table |
| Democritus | matter composed of indivisible and indestructible particles a.k.a. Discontinuous Theory of Matter |
| Aristotle | matter can continually be broken down into smaller and smaller pieces with out end a.k.a. Continuous Theory of Matter |
