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A light metal is any metal of relatively low density. More specific definitions have been proposed; none have obtained widespread acceptance. Magnesium, aluminium and titanium are light metals of significant commercial importance. Their densities of 1.7, 2.7 and 4.5 g/cm3 range from 19 to 56% of the densities of the older structural metals, iron (7.9) and copper(8.9).
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Light metals have low density and high strength-to-weight ratios. They are generally characterized by low toxicity in comparison to heavy metals, although beryllium is an exception.
Light metals are widespread in nature (more than 20 percent by mass), but because of their high chemical activity they exist only in the form of extremely strong compounds.
The core group of metals that are usually classed as light include aluminum, sodium, magnesium, beryllium, and lithium.