| A | B |
|---|
| Atoms | building blocks of matter |
| nucleus | center of an atom |
| protons | positively charged particles |
| neutrons | have no charge |
| electrons | negatively charged particles |
| element | a pure substance that cannot be broken down |
| isotopes | have a different number of neutrons |
| compound | a pure subtance formed when two or more elements combine |
| covalent bond | bond that forms when electrons are shared |
| molecule | when a compound is held together by covalent bonds |
| ion | gained or lost one or more electrons |
| ionic bond | electrical attraction between two oppositely charged atoms or groups |
| van der Waals forces | named for Dutch physicist |
