How can you tell if an element is a metal or a nonmetal??

Elements to the left of the line are considered metals. Elements just to the right of the line exhibit properties of both metals and nonmetals and are termed metalloids or semimetals. Elements to the far right of the periodic table are nonmetals. The exception is hydrogen (H), the first element on the periodic table.

Explanation:

looking at its metallic luster

Explanation:

Elements may be classified as either metals or nonmetals based on their properties. Much of the time, you can tell an element is a metal simply by looking at its metallic luster, but this isn't the only distinction between these two general groups of elements. Most elements are metals.