| Term | Definition |
|---|
| Atomic mass | The average mass of one atom of an element. |
| Periodic table | A chart of the elements showing the repeating pattern of their properties. |
| Nucleus | The central core of an atom containing protons and usually neutrons. |
| Proton | A small, positively- changed particle in the nucleus of the atom. |
| Neutron | A small particle in the nucleus of the atom, with no electrical charge. |
| Electron | A tiny, negatively-charged particle that moves around the nucleus of an atom. |
| Atomic mass unit (amu) | A unit used to measure the mass of particles in atoms; a proton or neutron has a mass of 1amu. |
| Atomic number | The number of protons in the nucleus of an atom. |
| Chemical symbol | A one- or two- letter representation with different properties. |
| Group | Elements in the same vertical column of the periodic table; also called family. |
| Family | Elements in the same vertical column of periodic table; also called group. |
| Period | A horizontal row of elements in the periodic table. |
| Valence electron | One of the electrons farthest away from the nucleus of the atom; these electrons are involved in a chemical reaction. |
| Malleable | A term used to describe material that can be hammered or rolled into shape. |
| Alloy | A mixture of two or more metals. |
| Ductile | A term used to describe a material that can be pulled out into a long wire. |
| Alkali metal | An element in Group 1 of the periodic table., Most reactive group of metals |
| Conductor | A substance that transmits heat or electricity easily. |
| Alkaline earth metal | An element in Group 2 of the periodic table., Second most reactive group of metals |
| Magnetic | A characteristic of those metals that are attracted to magnets and can be made into magnets. |
| Transition metal | An element in Groups 3 through 12 of the periodic table. |
| Reactivity | The ease and speed with which an element or compound combines with other elements and compounds. |
| Lanthanide | An element in the first row of the rare earth elements in the periodic table., they are pulled to the bottom |
| Corrosion | The gradual wearing away of a metal element due to a chemical reaction. |
| Actinide | An element in the second row of the rare earth elements in the periodic table., pulled to the bottom of the table |
| Nonmetal | An element that lacks most of the properties of metals. |
| Diatomic molecule | A molecule composed of two atoms of the same element., like O2 |
| Halogen family | The elements in Group 17 of the periodic table., most reactive nonmetals |
| Noble gas | An element in group 18 of the periodic table., they don't react |
| Metalloid | An element that has some of the characteristics of metals and some of the characteristics of nonmetals. |
| Semiconductor | An element that can conduct electricity under some conditions. |
| Plasma | A state of matter in which atoms are stripped of their electrons and the nuclei packed closely together. |
| Nuclear fusion | The process in which smaller nuclei combine into larger nuclei, forming heavier elements. |
| Supernova | An explosion of a massive star. |
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