| A | B |
|---|
| element | a substance that cannot be broken down into a simpler substance by ordinary chemical changes; consists of atoms of only one type |
| atom | the smallest unit of an element that has all the properties of the element; the basic building block of matter |
| proton | a positively charged particle located in an atom's nucleus |
| neutron | a neutral particle that has no electric charge located in an atom's nucleus |
| nucleus | the central region of an atom where most of the atom's mass is found in protons and neutrons |
| electron | a negatively charged particle located outside an atom's nucleusabout 2000 times smaller than either a proton or neutron |
| atomic number | the total number of protons in the nucleus of an atom |
| atomic mass number | the total number of protons and neutrons in an atom's nucleus |
| isotope | an atom of one element that has a different number of neutrons than another atom of the same element |
| ion | an atom or group of atoms that has a positive or negative electric charge; forms by atoms gaining or losing electrons |
