Lithium

Lithium is the lightest metal in the world and the lightest solid element on the periodic table. It is soft enough to cut with a kitchen knife, floats on both water and oil, and is found inside almost every rechargeable battery you own, from your phone to electric cars.

• Atomic Number33 protons, 3 electrons
• Atomic Mass7.0 uLightest of all solid elements
• State at Room TempSolidsoft enough to cut with a knife
• Density0.534 g/cm³floats on water (0.53 g/cm³)
• Melting / Boiling180.5°C / 1341.8°Cmelts at just 180°C
• Discovered1817Arfwedson, 1817

What is lithium?

Lithium is an alkali metal sitting at the top of Group 1 on the periodic table. Like all alkali metals, it has just one electron in its outer shell, which it gives away very easily. That makes it highly reactive, it hisses and fizzes when dropped in water, and must be stored under oil to stop it reacting with the air. Pure lithium is a silver-white metal with a shiny surface that tarnishes quickly.

Lithium gets its name from the ancient Greek word lithos, meaning stone. It was named this because it was first discovered inside a mineral rock, petalite, rather than in a plant or animal, as the alkali metals sodium and potassium had been. The symbol Li comes directly from the name.

Where you find lithium

On Earth

Lithium is never found as a pure metal in nature because it is too reactive. Instead, it is locked up inside minerals and dissolved in salty underground water called brine. The world's largest lithium reserves are in a triangle of desert between Chile, Argentina and Bolivia.

• Brine lakes. The Atacama Desert in South America contains vast underground pools of lithium-rich brine. Chile and Argentina together hold more than half the world's known lithium reserves.
• Hard-rock mines. Australia mines lithium from a mineral called spodumene. The Greenbushes mine in Western Australia is one of the world's largest single lithium mines.
• Seawater. The oceans contain dissolved lithium, but it is too dilute to be worth extracting economically today, though scientists are actively working on it.

How we use lithium

Lithium has become one of the most important metals of the 21st century, largely because of the electric vehicle revolution:

• Rechargeable batteries. Lithium-ion batteries power smartphones, laptops, electric cars and power tools. Lithium is chosen because it is very light and can store an enormous amount of energy for its size.
• Mental health medicine. Lithium carbonate is one of the most effective medicines for bipolar disorder, and has been prescribed by doctors since the 1950s.
• Lightweight alloys. Adding lithium to aluminium makes an alloy that is lighter and stronger, useful in aircraft, spacecraft and high-performance sports equipment.
• Special glass and ceramics. Lithium gives glass very low thermal expansion, so it does not crack when rapidly heated or cooled. This is used in telescope mirrors and ceramic hobs.

How it was discovered

Lithium was discovered in 1817 by the Swedish chemist Johan August Arfwedson while he was analysing a mineral called petalite found on a Swedish island. He noticed that when he burned the mineral it produced a distinctive crimson-red flame, a sign of a new element. His mentor Jöns Jacob Berzelius named it lithium from the Greek for stone.

Isolating the pure metal proved harder. It was first achieved by Humphry Davy and William Thomas Brande in 1821 using electrolysis. For much of the 19th century lithium was little more than a laboratory curiosity. Its extraordinary importance for energy storage was not recognised until the late 20th century.

Lithium is the lightest of all the alkali metals and the lightest solid element. Moving one step to the right on the same period brings you to beryllium, a harder and more toxic metal with very different properties.