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periodic law States that when the elements are arranged by increasing atomic number, there is a periodic repetition of their properties. group A vertical column of elements in the periodic table arranged in order of increasing atomic number; also called a family period A horizontal row of elements in the modern periodic table. representative elements Elements from groups 1, 2, and 13-18 in the modern periodic table, possessing a wide range of chemical and physical properties. transition elements Elements in groups 3-12 of the modern periodic table and are further divided into transition metals and inner transition metals. metal An element that is solid at room temperature, a good conductor of heat and electricity, and generally is shiny; most metals are ductile and malleable. alkali metals Group 1 elements, except for hydrogen, they are reactive and usually exist as compounds with other elements. alkaline earth metals Group 2 elements in the modern periodic table and are highly reactive. transition metal The elements in groups 3-12 that are contained in the d-block of the periodic table and, with some exceptions, is characterized by a filled outermost s orbital of energy level n, and filled or partially filled d orbitals of energy level n-1. rare earth metal A group of 17 chemically similar metals that includes the elements scandium and yttrium (atomic numbers 21 and 39, respectively) and the lanthanide elements (atomic numbers 57 through 71). lanthanide series In the periodic table, the f-block elements from period 6 that follow the element lanthanum. actinide series In the periodic table, the f-block elements from period 7 that follow the element actinium. nonmetals Elements that are generally gases or dull, brittle solids that are poor conductors of heat and electricity. halogen A highly reactive group 17 element. noble gas An extremely unreactive group 18 element. metalloid An element that has physical and chemical properties of both metals and nonmetals.