| 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. |
| electron | A negatively charged subatomic particle. |
| neutron | A subatomic particle with no charge and a mass of 1 amu; found in the nucleus of an atom. |
| proton | A positively charged subatomic particle found in the nucleus of an atom. |
| atmic mass | The weighted average of the masses of the isotopes of an element. |
| atomic number | The number of protons in the nucleus of an atom of an element. |
| nucleus | The tiny center of an atom composed of protons and neutrons. |
| valence electrons | The electrons that reside in the highest occupied orbital that determines an elements reactivity. |
| cathode ray | A stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure. |
| isotope | Atoms of the same element that have the same atomic number but different atomic masses due to a different number of neutrons. |
| mass number | The total number of protons and neutrons in the nucleus of an atom. |
| energy level | The specific energies an electron in an atom or other system can have. |
| electron configuration | The arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms. |
| group (family) | A vertical column on the periodic table. |
| period | A horizontal row on the periodic table. |
| periodic table | An organized chart of all the elements known to science. |
| periodic law | When the elements are arranged in order of increasing atomic number |
| cation | Any atom or group of atoms with a positive charge. |
| atomic radius | One-half the distance between the nuclei of two atoms of the same element when the atoms are joined. |
| ion | An atom or group of atoms that has a positive or negative charge. |
| photon | A quantum of light; a discrete bundle of electromagnetic energy that interacts with matter similarly to particles. |
| anion | Any atom or group of atoms with a negative charge. |
| electronegativity | The ability of an atom to attract electrons when the atom is in a compound. |
