| A | B |
|---|
| Atomic number | the number of protons in the nucleus of an atom |
| Atomic Mass | The number of protons and neutrons in the nucleus of an atom |
| isotopes | atoms of the same element with different number of neutrons |
| ions | an atom with an electrical charge |
| Valence shell | the outside energy shell of any atom |
| Periodic table | a list of all the elements in the universe |
| periods | the rows of the periodic table |
| groups | the columns of the periodic table |
| alkali metals | most of the elements in group 1 |
| alkaline earth metals | all of the elements of group 2 |
| transition metals | strong and shiny |
| halogens | reactive elements in group 17 |
| inert or noble gases | group 18 elements |
| radioactive decay | when the nucleus of an unstable atom partially breaks down |
| transmutation | when an atom changes into a new element |
| half-life | when half a group of radioactive atoms will decay in a specific time |
| alpha particles | radioactive particle that can be stopped by paper |
| beta particles | radioactive particles that can be stopped by wood |
| gamma rays | radioactive particles that can be stopped by lead |
