| A | B |
|---|
| atom | the basic unit of matter |
| proton | a positively charged particle inside the nucleus of an atom |
| electron | a negatively charged particle orbiting around the nucleus of an atom |
| John Dalton | developed the first atomic theory |
| Democritus | believed everything was made of atoms, and they could not be broken down any further |
| Ernest Rutherford | discovered the nucleus of atom through his gold foil experiment |
| Neils Bohr | Believed electrons orbit around the nucleus in a circular motion in levels, jumping from level to level |
| atomic number | tells how many protons an element has |
| Periodic Table of Element | where all known elements are listed in order according to families and atomic numbers |
| neutron | a particle inside the nucleus of an atom with no charge |
| Chadwick & Currie | discovered the neutron |
| J.J. Thomson | discovered the electron |
| average atomic mass | mass of all the isotopes of an element |
| mass number | rounded number that tells the # of protons & neutrons in the nucleus of an atom |
| quark | Any of a group of six elementary particles having electric charges of a magnitude one-third or two-thirds that of the electron, regarded as constituents of protons and neutrons |
