What Is The Lightest Metal? - Science Notes

Can you name the lightest metal? Most metals are heavy or dense, yet some metals can float on water while others are nearly as light as air. Learn about the lightest elemental metal and the lightest alloy.

Key Points: Lightest Metal

• Being light is the same as having low density.
• The lightest metal is lithium, which is a pure element with a density of 0.534 g/cm3. Lithium is so light that it can float on water.
• The 5 lightest metals that are elements are lithium, potassium, sodium, rubidium, and calcium. Of these, only lithium, potassium, and sodium have low enough density to float on water.
• Some alloys are also light, either because of the way their atoms pack or because of their manufactured structure. Light alloys include magnesium alloy (~1.8 g/cm3) and aluminum-lithium alloy (2.58 g/cm3).
• Microlattice has a density of only 0.0009 g/cm3. Even though it consists of a relatively heavy nickel-phosphorus alloy (9.0 g/cm3), it consists of hollow tubes that minimize its mass per volume.

Light Means Low Density

When we talk about a material being lightweight, what we’re really discussing is density. Density is the amount of matter per unit of volume. The less matter there is in a space, the lighter the substance is. So, metals with high density are heavy. For example, the density of lead is 11.34 g/cm3. Metals with low density are light. These metals include lithium, beryllium, sodium, magnesium, and aluminum.

Lightest Metal That Is an Element

So, the lightest metallic element is the one with the lowest density. The lightest or least dense element that is a metal is lithium. Lithium is atomic number 3 on the periodic table, with a density of 0.534 g/cm3. This is comparable to the density of pine wood. The density of water is about 1 g/cm3, so lithium floats on water. But, like other alkali metals, lithium is highly reactive, so it rapidly reacts to release heat and form lithium hydroxide and hydrogen gas. It also burns in air, so the pure metal is stored under oil (where it also floats) or in an inert atmosphere.

Under ordinary conditions, only two other metallic elements are light enough to float on water: potassium and sodium. The density of potassium is 0.862 g/cm3, while the density of sodium is 0.971 g/cm3. Lithium, potassium, and sodium are all alkali metals. The reason they are so light is because these elements are the first atoms in their period on the periodic table to gain an additional electron shell. The shell makes the atoms large for their mass.

What about hydrogen? It’s in the alkali metal group and is even lighter than lithium. Normally, hydrogen behaves as a nonmetallic gas. However, under certain conditions hydrogen forms a solid metal with a density of 0.0763 g/cm3. It would be the lightest metal if it existed naturally on Earth!

Lightest Metal Table of Values

Here is a table of the lightest metal density values. The light includes both pure elements and alloys. Note that density is not a fixed value. Density varies according to temperature, purity, composition, and structure.

In industry, “light metal” typically references metals with low density and practical applications. Many of the lightest metals burn in air or water, so in practical terms, light metals are magnesium and its alloys, aluminum and its alloys, and the other metals below it on the list.

Lightest Metal Alloy

Even a relatively dense material can be light. For example, an aluminum boat floats on water, even though aluminum is a metal that is more dense than water. So, the lightest metal in the world is not actually made of the least dense material!

The lightest metal on Earth is an alloy rather than an element. It is a lattice of nickel phosphorus tubes (Microlattice) that was invented by researchers at the University of California at Irvine. The density of Microlattice is 0.0009 g/cm3 or 9 mg/cm3. With the air removed, the density of the metal structure is only 2.1 mg/cm3. It is one hundred times lighter than polystyrene foam and about 1.76 times heavier than air at 25 °C. A piece of the alloy can rest on a dandelion without bending it.

A chunk of nickel phosphorus has a density of 9.0 g/cm3. The reason the lattice is so light is because it consists of hollow tubes in a lattice that is 99.99% air and only 0.01% metal. Researchers coated a template with alloy and then etched away the template, leaving hollow tubes only around 100 nanometers thick (a thousand times thinner than a human hair). Microlattices show tremendous promise as thermal insulators and acoustic and vibration dampeners.

References

• Brandes, E.A.; Brook, G.B. (eds) (1998). Light Metals Handbook. Butterworth Heinemann. Oxford. ISBN 0-7506-3625-4.
• Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
• Polmear, I. (2006). Light Alloys: From Traditional Alloys to Nanocrystals (4th ed.). Butterworth Heinemann. Oxford. ISBN 0-7506-6371-5.
• Schaedler, T. A.; Jacobsen, A. J.; Torrents, A.; Sorensen, A. E.; Lian, J.; Greer, J. R.; Valdevit, L.; Carter, W. B. (October 12, 2011). “Ultralight Metallic Microlattices”. Science. 334 (6058): 962–5. doi:10.1126/science.1211649

Related Posts