| A | B |
|---|
| element | substance that cannot be broken down into simpler substances |
| electron | negatively-charged particle that exists in an electron cloud formation around an atom's nucleus |
| proton | positively-charged particle in the nucleus of an atom |
| neutron | electrically-neutral particle that has the same mass as a proton and is found in an atom's nucleus |
| electron cloud | region surrounding the nucleus of an atom, where electrons are most likely to be found |
| atomic number | number of protons in the nucleus of an atom of a given element |
| isotopes | atoms of the same element that have different numbers of neutrons |
| mass number | the sum of neutrons and ptotons in the nucleus of an atom |
| radioactive decay | release of nuclear particles and energy from unstable atomic nuclei |
| transmutation | the changing of one element into another through radioactive decay |
| half-life | time needed for one-half of the mass of a sample of a radioactive isotope to decay |
