Typically the greater the reactivity of a metallic element, the lesser the likelihood of its existance as an uncombined element. There isn't a pattern of reactivity to uncombined forms in non-metallic elements. For examples: Gold (Au) has an extremely low reactivity, so it is commonly found uncombined with other elements. In fact Gold is a "Noble" metal. Like the "Noble" gases, it doesn't naturally form compounds with other elements. As you go up the reactivities to Iron, Copper and Aluminum, they can exist for a time as uncombined elements, but ultimately their reactivities lead to them combining into compounds; Iron to rust, Copper to Cupric Oxide (The color of the Statue of Liberty), and Aluminum to Aluminum oxide (a transparent micron thick coating). When you get to the Alkali Earth Metals, and the Alkaline metals, (Mg and Ca former, Na and Li latter) you have elements that never exist as uncombined elements, they always react quickly to form compounds.