Which is the lightest metal?

The lightest metal known is lithium (Li). It is the first metal in the alkali metal group of the periodic table, with an atomic number of 3 and an atomic mass of approximately 6.94 u. Lithium has a very low density of 0.534 g/cm³, which makes it lighter than water. In fact, lithium is so light that it can float on water if it did not react so vigorously with it.

Lithium is a soft, silvery-white metal and is highly reactive and flammable. Because of its position at the top of Group 1 (the alkali metals), lithium shares similar properties with sodium and potassium but is the least dense among them. Its low density and high electrochemical potential make it extremely useful in various modern applications.

One of the most important uses of lithium is in rechargeable lithium-ion batteries, which power mobile phones, laptops, and electric vehicles. It is also used in lightweight alloys, pharmaceuticals, and heat-resistant glass. Despite being a metal, lithium is so soft that it can be cut easily with a knife.

Comparatively, sodium and magnesium are denser and heavier than lithium, while aluminium is a lightweight metal but still about five times denser than lithium. The unique combination of lightness, reactivity, and electrical properties makes lithium one of the most important elements in modern technology.

In simple terms, lithium is the lightest and one of the most reactive metals, playing a key role in both chemistry and energy-related industries. Its study helps us understand atomic structure, metallic bonding, and the periodic trends that define the behavior of all elements.