Periodic tableA chart of all chemical elements currently known, organized by their properties.Elementpure substance that consists entirely of one type of atomatomthe smallest unit of an element that maintains the properties of that elementperiodshorizontal rows on the periodic tablegroupsvertical columns on the periodic tablemetalshiny, malleable, ductile and good conductorsLusterreflecting lightmalleableable to be hammered into thin sheetsductilecan be pulled into long wiresconductivitythe ability of an object to transfer heat or electricity to another objectreactivitythe ease and speed with which an element combines or reacts with other elements and compoundscorrosionthe gradual wearing away of a metal element due to a chemical reactionalkali metalsvery reactive, not found alone in nature, potassium and sodium are examplesalkaline earth metalshard, grey-white, good conductors of electricity, calcium and magnesium are examplesTransition metalsmost are hard and shiny, less reactive, examples are iron, copper, nickel and goldmixed metalsleast reactive, examples are tin, lead and aluminumlanthanidesthe first period below the periodic table, they are mixed with more common metals to form alloysalloya mixture of a metal with at least one other elementactinidesthe period below lanthanides, very unstablesynthetic elementsnot found naturally on earth, all elements higher than 92