| A | B |
|---|
| atom | the smallest particle of an element that retains its identity in a chemical reaction |
| Dalton's atomic theory | the first theory to relate chemical changes to events at the atomic level |
| electrons | negatively charged subatomic particles |
| protons | positively charged subatomic particles |
| neutrons | subatomic particles with no charge |
| nucleus | the tiny central core of an atom |
| atomic number | the number of protons in the nucleus of an atom of an element |
| mass number | the total number of protons and neutrons in an atom |
| isotopes | atoms of the same element that have the same number of protons but different numbers of neutrons |
| atomic mass unit | one-twelfth the mass of a carbon-12 atom |
| atomic mass | a weighted average mass of the atoms in a naturally occurring sample of an element |
| energy levels | the specific energies an electron in an atom can have |
| ion | atoms with a positive or negative charge |
| cation | positively charged ion |
| anion | negatively charged ion |
| radioactivity | the process by which nuclei emit particles and rays |
| radiation | the penetrating rays and particles emitted by a radioactive source |
| radioisotopes | an isotope that has an unstable nucleus and undergoes radioactive decay |
| alpha particle | radioactive particle consisting of 2 protons and 2 neutrons |
| beta particle | radioactive particle similar to an electron resulting from the breaking apart of a neutron in an atom |
| gamma ray | a high-energy photon emitted by a radioisotope |
| half-life | time required for one-half of the nuclei of a radioisotope sample to decay to products |
| ionizing radiation | radiation with enough energy to knock electrons off some atoms to produce ions |
| Geiger counter | a device that uses a gas-filled metal tube to detect radiation |
| scintillation counter | a device that uses a phosphor-coated surface to detect radiation |
| film badge | a device that uses several layers of photographic film to detect radiation |
| fission | the splitting of a nucleus into smaller fragments |
| fusion | the process of combining nuclei to produce a nucleus of greater mass |
| atomic orbital | region of space in which there is a high probability of finding an electron |
| aufbau principle | electrons occupy the orbitals of lowest energy first |
| Pauli exclusion principle | an atomic orbital may describe (hold) at the most two electrons |
| Hund's rule | electrons occupy orbitals of the same energy in a way that makes the total number of electrons with the same spin direction as large as possible |
| crest | highest point of a wave |
| trough | lowest point of a wave |
| amplitude | the height of a wave from zero to the crest |
| wavelength | the distance between adjacent crests |
| frequency | the number of waves that pass a given point per second |
| hertz | unit of frequency meaning one cycle per second |
| electromagnetic radiation | all waves that travel at 3.00 x 10^8 m/s in a vacuum |
| spectrum | wavelengths of visible light that are separated when a beam of light passes through a prism |
| atomic emission spectrum | the pattern formed when the different frequencies of light are emitted by an element |
| ground state | the lowest possible energy of the electron |
| excited state | electrons in a higher energy level than its lowest possible state |
| photon | a quantum of light |
| quantum | amount of energy required to move an electron from one energy level to another |
