alkali metals: Group 1A metals

alkaline earth metals: Group 2A metals

anion: ion with a negative charge, always larger than atom it forms from

atomic radius: one half the distance between the nuclei of two atoms of the same element when the atoms are joined, expresses size of atoms

cation: an ion with a positive charge, always smaller than the atom it forms from

electronegativity: ability of an atom to attract electrons when the atom is in a compound, calculated using factors like ionization energy

halogens: Group 7A nonmetals, includes general class of compounds called salts, very reactive

inner transition metal: appear below the main body of the periodic table, characterized by f orbitals that contain electrons and generally also have electrons in highest occupied s sublevel

ion: an atom or group of atoms that has a positive or negative charge, not neutral, formed when electrons are transferred between atoms

ionization energy: the energy required to remove an electron from an atom, measured when an element is in its gaseous state

metalloids: elements that border the line between metals and nonmetals, usually shaded green

metals: 80% of the periodic table, good conductors of heat and electric current, high luster/sheen due to ability to reflect light, ductile, malleable, solid at room temperature except mercury (Hg)

noble gases: elements in Group 8A of periodic table, aka inert gases, quite stable and rarely in reactions (s and p sublevels completely filled)

nonmetals: elements in upper-right corner, most gases and a few solids (sulfur and phosphorous) and only bromine is liquid, poor conductors of heat and electric current (except carbon), often brittle and shatter if hammered

periodic law: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

representative elements: elements in Groups IA-7A, so-called as they display a wide range of physical/chemical properties (metals, non-metals, or metalloids), most solids but few gases at room temperature and one (bromine) is liquid, s and p sublevels of highest occupied energy level are not filled

transition metal: Group B elements that are usually displayed in main body of a periodic table (e.g. copper, silver, gold & iron), characterized by presence of electrons in d orbitals and generally also have electrons in highest occupied s sublevel