| A | B |
|---|
| atom | the building blocks of matter |
| nucleus | located at the center of the atom, consists of protons and neutrons |
| proton | positively charged particle located in the center of an atom |
| electron | negatively charged particle located outside the nucleus |
| neutron | particle with no charge located in the center of an atom |
| element | a pure substance that cannot be broken down into other substances by physical or chemical means |
| isotopes | atoms of the same element that have different numbers of neutrons, but the same number of protons |
| compound | a pure substance formed whern two or more different elements combine |
| covalent bond | chemical bond which forms when two atoms share electrons |
| molecule | a compound in which the atoms are held together by covalent bonds |
| ion | an atom that has gained or lost an electron and carries an electric charge |
| ionic bond | an electrical attraction between two oppositely charged atoms or groups of atoms |
| van der Waals forces | the attractive force between the positive and negative regions of different molecules |
