| A | B |
|---|
| nucleus | the tiny central core of an atom: contains protons and neutrons |
| proton | small positively-charged particle in the nucleus of an atom |
| neutron | small uncharged particle in the nucleus of an atom |
| electron | tiny negatively-charged high-energy particle that moves in the space outside the nucleus of an atom |
| atomic number | the number of protons in an atom; identifies the element |
| atomic mass unit | the unit for the mass of particles in atoms |
| valence electron | the electrons that are farthest from the nucleus and are involved in chemical reactions |
| electron dot diagrams | dots placed around the element symbol represent the valence electrons |
| mass number | the sum of the protons and neutrons in the nucleus of an atom |
| isotope | an atom with the same number of protons but with a different number of neutrons |
| atomic mass | the average mass of the atoms of an element |
| periodic table | an arrangement of the elements in order of atomic number in which elements with similar properties are grouped in columns |
| group | elements in the same vertical columns; also called families; have similar properties |
| family | elements in the same vertical column; also called groups |
| period | a horizontal row of elements in the periodic table |
| malleable | a material that can be pounded into shape |
| ductile | a material that can be pulled into a long wire |
| conductor | a substance through which electrons move freely transmitting heat or electricity |
| magnetic | characteristic of metals that are attracted to magnets and can be made into magnets |
| corrosion | the gradual wearing away of a metal due to chemical reaction |
| alkali metal | an element in Group 1; highly reactive |
| alkaline earth metal | an element in Group 2; very reactive |
| transition metal | an element in Groups 3 - 12 |
| lanthanide | a group of elements in the first row of the rare earth elements |
| actinide | a group of elements in the second row of the rare earth elements |
| nonmetal | an element that lacks most of the properties of metals |
| diatomic molecule | a molecule composed of two identical atoms |
| halogen family | elements in Group 17; highly reactive |
| noble gas | an element in Group 18; unreactive |
| metalloid | an element with some of the characteristics of metals and some characteristics of nonmetals |
| semiconductor | can conduct electricity under some conditions |
| plasma | a state of matter in which atoms are stripped of their electrons and the nuclei are packed closely together |
| nuclear fusion | the process in which smaller nuclei combine into larger nuclei releasing much energy |
| supernova | an explosion that breaks apart a massive star |
