| A | B |
|---|
| Alpha particle | A particle with two protons and two neutrons, with a 2+ charge; is equivalent to a helium-4 nucleus and is emitted during radioactive decay |
| beta particle | a particle equivalent to an electron, with a -1 charge, emitted during radioactive decay |
| gamma ray | High-energy radiation that has no electrical charge and no mass, and accounts for most of the energy lost during radioactive decay |
| Atom | The smallest particle of an element that retains all the properties of that element |
| atomic mass | the weighted average mass of the isotopes of that element |
| atomic mass unit | One-twelfth the mass of a carbon-12 atom |
| cathode ray | A ray of radiation that originates from the cathode and travels to the anode of a cathode ray tube |
| Dalton’s Atomic Theory | A theory proposed in 1808, based on numerous scientific experiments, that marked the beginning of the development of modern atomic theory |
| Electron | A negatively charged, fast-moving particle with an extremely small mass that is found in all forms of matter and moves through the empty space surrounding an atom's nucleus. |
| Isotope | Atoms of the same element with the same number of protons but different numbers of neutrons |
| mass number | The number after an element's name, representing the sum of its protons and neutrons |
| neutron | A neutral subatomic particle in an atom's nucleus that has a mass nearly equal to that of a proton |
| nuclear reaction | A reaction that involves a change in the nucleus of an atom |
| radiation | The rays and particles--alpha and beta particles and gamma rays--that are emitted by radioactive materials. |
| nucleus | The very small, positively charged, dense center of an atom; contains positively charged protons, neutral neutrons, and is surrounded by empty space through which negatively charged electrons move |
| proton | A subatomic particle in an atom's nucleus that has a positive charge of 1+ |
| radioactive decay | A spontaneous process in which unstable nuclei lose energy by emitting radiation |
| fission | the splitting of a nucleus into smaller, more stable fragments, accompanied by a large release of energy |
| fusion | The process of binding smaller atomic nuclei into a single larger and more stable nucleus |
| atomic number | number of protons in the nucleus |
| period | horizontal row in the periodic table |
| group | vertical row in the periodic table |
| periodic table | arrangement of elements separated into groups based on repeating properties |
