What Is the Lightest Metal?

Metals That Float on Water

The lightest elemental metal is lithium, but the lightest metal overall is an alloy that consists of metal and air.
The lightest elemental metal is lithium, but the lightest metal overall is an alloy that consists of metal and air. Huw Jones / Getty Images

You may think of metals as heavy or dense. This is true of most metals, but there are some that are lighter than water and even some that are nearly as light as air. Here's a look at the world's lightest metal.

Lightest Elemental Metal

The lightest or least dense metal that is a pure element is lithium, which has a density of 0.534 g/cm3. This makes lithium nearly half as dense as water, so if lithium was not so reactive, a chunk of the metal would float on water.

Two other metallic elements are less dense than water. Potassium has a density of 0.862 g/cm3 while sodium has a density of 0.971 g/cm3.  All of the other metals on the periodic table are denser than water.

While lithium, potassium, and sodium are all light enough to float on water, they are also highly reactive. When placed in water, they burn or explode.

Hydrogen is the lightest element because it consists simply of a single proton and sometimes a neutron (deuterium). Under certain conditions, it forms a solid metal, which has a density of 0.0763 g/cm3. This makes hydrogen the least dense metal, but it isn't generally considered a contender for "lightest" because it doesn't exist as a metal naturally on Earth.

Lightest Metal Alloy

Although the elemental metals may be lighter than water, they are heavier than some alloys. The lightest metal is a lattice of nickel phosphorous tubes (Microlattice) that was developed by researchers at the University of California Irvine.

This metallic micro-lattice is 100x lighter than a piece of polystyrene foam (e.g., Styrofoam). One famous photograph shows the lattice resting on top of a dandelion that has gone to seed.

Even though the alloy consists of metals that possess ordinary density (nickel and phosphorus), the material is extremely light.

This is because the alloy is arranged in a cellular structure, consisting of 99.9% open air space. The matrix is made of hollow metal tubes, each only about 100 nanometers thick or around a thousand times thinner than a human hair. The arrangement of tubules gives the alloy an appearance sort of light a mattress box spring. Although the structure is mostly open space, it's very strong because of how it can distribute weight. Sophie Spang, one of the research scientists who helped design Microlattice, compares the alloy to human bones. Bones are strong because they are mainly hollow rather than solid.

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Helmenstine, Anne Marie, Ph.D. "What Is the Lightest Metal?" ThoughtCo, Jan. 25, 2018, thoughtco.com/what-is-the-lightest-metal-608450. Helmenstine, Anne Marie, Ph.D. (2018, January 25). What Is the Lightest Metal? Retrieved from https://www.thoughtco.com/what-is-the-lightest-metal-608450 Helmenstine, Anne Marie, Ph.D. "What Is the Lightest Metal?" ThoughtCo. https://www.thoughtco.com/what-is-the-lightest-metal-608450 (accessed March 20, 2018).