| A | B |
|---|
| physical properties | characteristic that can be observed without changing the composition of a substance |
| chemical property | characteristics that determines how a substance reacts with other substances |
| physical change | change that does not affect the composition of a substance |
| chemical change | change that forms new substances with new properties |
| electron | a tiny, negatively charged particle outside the nucleus of an atom |
| nucleus | the dense, positively charged core of an atom |
| neutral | having no charge |
| neutron | uncharged particle in the nucleus of an atom |
| protron | positively charged particle in the nucleus of an atom |
| quark | one of two basic building blocks of an atom |
| chemical bond | strong attraction between two atoms |
| atomic number | number of protrons in an atom of an element |
| isotope | one of a group of atoms of an element with the same number of protrons but different numbers of neutrons |
| mass number | the total number of protrons and neutrons in the nucleus of an atom |
| periodic table | an arrangement of the elements by increasing atomic number |
| radioactive element | an element that naturally breaks down into a less massive element, giving off rays of energy and streams of particles |
| John Dalton | proposed the first atom model |
| Mendeleev | organized the periodic table by atomic numbers |
