Lithium – facts and properties
- Symbol
- Li
- Atomic number
- 3
- Atomic mass
- 6.94 u
- Period
- 2
- Group
- 1
- Category
- alkali metal
- Electron configuration
- [He] 2s¹
- Electronegativity
- 0.98
- Atomic radius
- 167 pm
- Valence electrons
- 1
- State at standard conditions
- solid
- Melting point
- 180.5 °C
- Boiling point
- 1342 °C
- Density
- 0.534 g/cm³
- Discovered
- 1817
Lithium is the lightest metal in the periodic table and so soft that it can be cut with a knife. With atomic number 3 it heads the alkali metals, the most reactive group of metals. For most of the twentieth century lithium was a niche material for glass, grease and ceramics. The rechargeable battery changed that: today lithium powers phones, laptops and electric cars, and demand for it has reshaped mining in South America and Australia.
Position in the periodic table
Sources and extraction
Lithium never occurs as a free metal because it reacts with air and water. It is widely distributed in the Earth's crust but rarely concentrated. Hard-rock deposits contain it in minerals such as spodumene, petalite and lepidolite, which occur in coarse-grained granites called pegmatites; Australia is the largest producer from this type of source. The second major source is brine. Beneath the salt flats of the Andes, in the so-called lithium triangle of Bolivia, Chile and Argentina, groundwater rich in dissolved lithium salts lies just below the surface. Seawater also contains lithium, but at concentrations too low to be worth extracting so far. In Germany, projects are testing whether lithium can be recovered from hot geothermal brines in the Upper Rhine valley.
Brine is pumped into shallow ponds, where the desert sun evaporates the water over many months until lithium carbonate can be precipitated from the concentrated solution. Ore is crushed, roasted and leached with acid to produce the same compound. Lithium carbonate and lithium hydroxide are the forms traded for battery production. The metal itself is obtained by electrolysing a molten mixture of lithium chloride and potassium chloride. Lithium was discovered in 1817 by Johan August Arfwedson while analysing the mineral petalite from a Swedish mine. Its name comes from the Greek lithos, meaning stone, because unlike sodium and potassium it was first found in a rock rather than in plant ashes.
Properties and reactions
Lithium has the electron configuration [He] 2s¹: a filled inner shell and one outer electron that it gives up easily to form the Li⁺ ion. Its electronegativity of 0.98 is low, as expected for an alkali metal. The metal is silvery white and so light, with a density of 0.534 g/cm³, that it floats on water and on oil. It melts at 180.5 °C and boils at 1342 °C, both higher than for any other alkali metal. In the periodic table it occupies period 2 and group 1.
A freshly cut surface tarnishes within minutes because lithium reacts with oxygen to form the oxide and, unusually among alkali metals, with nitrogen to form lithium nitride. Dropped into water it fizzes steadily, producing lithium hydroxide and hydrogen gas. The reaction is much gentler than with sodium or potassium and the metal does not melt, but the solution becomes strongly alkaline and the hydrogen can ignite. Lithium colours a flame a deep crimson, which is the classic flame test for the element. It is stored under mineral oil or argon to keep it away from air and moisture. In several respects lithium resembles magnesium, its diagonal neighbour in the periodic table: both form carbonates and phosphates of low solubility and both combine directly with nitrogen. This diagonal relationship is a useful pattern to remember when comparing the lighter elements.
Uses in everyday life and technology
Batteries now consume most of the world's lithium. In a lithium-ion cell, lithium ions shuttle between a graphite electrode and a metal-oxide electrode as the battery charges and discharges. Because lithium is so light and gives up its electron so readily (chemists say it has a strongly negative electrode potential), these cells store more energy per kilogram than any other commercial rechargeable type. They sit inside smartphones, laptops, e-bikes and electric vehicles, and increasingly in home and grid storage for solar power.
Lithium had many uses before the battery boom and still does. Lithium carbonate and lithium oxide lower the melting point of glass and ceramics and make them resistant to sudden temperature changes, which is why glass-ceramic hobs contain lithium. Lithium stearate thickens lubricating greases that stay stable from freezing cold to engine heat. Aluminium-lithium alloys are lighter than ordinary aluminium and are used in aircraft structures. Lithium hydroxide absorbs carbon dioxide from the air in submarines and spacecraft. In medicine, lithium salts have been prescribed for decades to stabilise mood in bipolar disorder. The isotope lithium-6 is the raw material for tritium, which fusion research requires. With electric mobility driving demand, recycling of spent batteries is becoming an industry in its own right.
Molecules containing this element
- Lithium hydride LiH
- Lithium hydroxide LiOH
- Lithium bromide LiBr
Quick question
Which element has the smaller atomic radius in period 2?
FAQ
Why are lithium-ion batteries so powerful?
Lithium is the lightest metal and gives up its outer electron very readily, so a cell delivers a high voltage for little weight. Its ions are small enough to slip in and out of layered graphite and metal-oxide structures without damaging them, which allows the battery to be recharged hundreds or thousands of times.
Is lithium dangerous?
The metal reacts with water and moist air and can start fires that water will not put out. Lithium salts are far less reactive, but in larger doses they are toxic, which is why patients taking lithium medication have their blood levels monitored. Damaged or overheated lithium-ion batteries can catch fire, so they must never be thrown into household waste.
Where does the lithium in batteries come from?
Most of it is mined in Australia from the mineral spodumene or pumped from brines beneath the salt flats of Chile and Argentina. Much of the refining takes place in China. Europe is developing its own sources, including geothermal brines and hard-rock deposits, and building up battery recycling to reduce its dependence on imports.