| A | B |
|---|
| protons | a subatomic particle identical with the nucleus of the hydrogen atom; positively charged |
| neutrons | an uncharged particle found in the nucleus of an atom |
| electrons | a subatomic particle in an atom that is negatively charged and occupies energy levels in an atom |
| subatomic particles | particles that smaller than an atom |
| nucleus | the center core of an atom that contains protons and neutrons |
| atomic theory | the theory that states that all matter is composed of tiny particles called atoms |
| atomic number | the number of protons in an atom |
| mass number | the total number of protons and neutrons that are in the nucleus of an atom |
| periodic table of elements | a table that visually organizes the similarites between all known elements |
| isotopes | forms of the same element that have different numbers of nuetrons and different mass numbers |
| strong nuclear force | the force that holds protons together when they are very close together. |
| energy levels | a region around the nucleus of an atom where electrons are most likely to be found. |
| groups of elements | elements that exhibit similar chemical properties; columns on the periodic table |
| valence electrons | the electrons in an atom that are involved in the formation of chemical bonds |
| chemical symbol | an abbreviation that represents the name of an element |
| atomic mass unit | the mass of 1/12 of a carbon-12 atom |
| atomic mass | the average mass of all the known isotopes of an element |
