| A | B |
|---|
| alkali metal | any metal in Group 1 (1A) of the periodic table |
| alkaline earth metal | any metal in Group 2 (2A) of the periodic table |
| atom | the smallest particle of an element that retains the properties of that element |
| atomic mass | the weighted average of the masses of the isotopes of an element |
| atomic mass unit (amu) | a unit of mass equal to one-twelfth the mass of a carbon-12 atom |
| atomic number | the number of protons in the nucleus of an atom of an element |
| cathode ray | a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure |
| Dalton's Atomic Theory | the first theory to relate chemical changes to events at the atomic level |
| electron | a negatively charged subatomic particle |
| group | a vertical column of elements in the periodic table; members have similar chemical and physical properties |
| halogen | any member of the nonmetallic elements in Group 17 (7A) of the periodic table |
| inner transition metal | an element in the lanthanide and actinide series;characterized by addition of electrons to f orbitals |
| 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 |
| metal | one of a class of elements that includes a large majority of the known elements;characteristically lustrous, malleable, ductile, and good conductors of heat and electricity |
| metalloid | one of a class of elements having properties intermediate to metals and nonmetals |
| neutron | a subatomic particle with no charge and a mass of 1 amu; found in the nucleus of the atom |
| noble gas | any member of a group of gaseous elements in Group 18 (0) |
| nonmetal | one of a class of elements that are not lustrous and are generally poor conductors of heat and electricity; grouped on the right side of the periodic table |
| nucleus | the dense central portion of an atom, composed of protons and neutrons |
| period | a horizontal row of elements in the periodic table |
| periodic law | when the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties |
| periodic table | an arrangement of elements into rows and columns according to similarities in their properties |
| proton | a positively charged subatomic particle found in the nucleus |
| representative elements | Groups 1,2, 13-17; Group "A" elements on the periodic table; together, these elements, which have only partially filled outermost s and p sublevels, illustrate the entire range of chemical properties |
| transition metal | Groups 3-12: "B" Groups; characterized by addition of electrons to d sublevels |
