Atomic number 3

Lithium

Li
+ phase
− phase

Shells Orbitals 2s

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3 electrons in 2 shells: 2, 1.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Alkali metal
Period: 2
Group: 1
Block: s
Standard atomic weight: 6.94(6) Da
Electron configuration: [He] 2s¹
Phase at 25 °C: solid
Melting point: 180.5 °C
Boiling point: 1330 °C
Density: 0.534 g/cm³
Electronegativity (Pauling): 0.98
Discovered: 1817, Johan August Arfwedson

Neighbours in the table

He Be

Lithium is the point where the periodic table opens a second shell. Its first two electrons fill the 1s orbital as helium’s do. The third, OpenStax says, must take the next orbital up, 2s, giving [He] 2s¹ and shells of 2 and 1. Sodium and potassium repeat the arrangement, one electron outside a filled core, and that shared count of valence electrons is why the group reacts alike.

Alkali metals have the largest atoms of their periods and the lowest first ionisation energy, the energy needed to remove one electron. OpenStax says that pairing makes the outer electron easy to remove. What remains is Li⁺, an ion with helium’s two electrons and no more; the next electron sits in the core and costs far more. Reactivity climbs down the group, OpenStax says, so lithium, the first member, is the least reactive.

At 0.534 g/cm³ it has the lowest density of any metal on OpenStax’s and Los Alamos’s pages, and floats in paraffin oil because the oil is denser. It melts at 180.50 °C; OpenStax reads the group’s low melting points as weaker metallic bonding, the hold a metal’s nuclei keep on their shared electrons. Nitrogen gas, held shut by a triple bond, reacts with almost nothing at room temperature. Lithium is an exception, OpenStax notes: it makes the nitride Li₃N.

Where it is found

Free lithium metal does not exist in nature; OpenStax puts that down to the group’s reactivity. Jefferson Lab, in PubChem’s record, gives the crust 20 milligrams per kilogram and seawater 0.18 milligrams per litre. Los Alamos finds traces in almost every igneous rock and in many mineral springs; its main minerals are lepidolite, spodumene, petalite and amblygonite.

Today’s supply comes from minerals and from brine, salt-laden groundwater. The US Geological Survey’s main producers of 2024 are nine mineral operations in Australia, two brine operations in Chile, four in Argentina and twelve in China, seven of them mineral. Australia mined 88,000 metric tons of lithium content, Chile 49,000 and China 41,000; world output outside the United States rose 18 per cent to about 240,000 tons.

The only commercial-scale US producer, a Nevada brine operation, has its output withheld; imports, almost all from Chile and Argentina, cover over half of US use. Los Alamos and Jefferson Lab both have the metal made by electrolysis of molten lithium chloride. Group 1 ions are very hard to reduce, to hand an electron back to, which OpenStax says is why electrolysis is needed.

Why it matters

Johan August Arfwedson found lithium in the mineral petalite in 1817, the year Los Alamos and Jefferson Lab give; the CIAAW history in PubChem’s record says 1818. The name comes from lithos, stone, because, CIAAW says, lithium was then thought to exist only in minerals. The same record tells the isolation two ways. Jefferson Lab credits William Brande and Humphry Davy, by electrolysis of the oxide, and CIAAW names Robert Bunsen and Augustus Matthiessen, in 1855.

Batteries took 87 per cent of the world’s lithium in 2024 by the US Geological Survey’s estimate. In a lithium-ion cell the element travels as ions. OpenStax writes the charged anode as LiC₆, lithium held in carbon, and the cathode as lithium cobalt oxide. On discharge Li⁺ leaves the carbon for the oxide, and the cell gives about 3.7 V. That is one cathode chemistry of several; the survey’s cobalt summary has cobalt-free iron and phosphorus cathodes holding a significant share in China.

A pacemaker is the other end of the scale: PubChem’s isotope notes record that nuclear batteries powered pacemakers until the mid-1980s, when long-lasting lithium batteries took over. Los Alamos lists lithium in the glass of the 200-inch Palomar telescope and lithium carbonate as a prescribed medicine for bipolar disorder. Jefferson Lab adds lithium hydroxide scrubbing carbon dioxide from spacecraft air.

Properties

Properties of lithium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	3
Standard atomic weight	6.94(6) Da	Da	IUPAC/CIAAW 2024
Melting point	180.5 °C	°C	Los Alamos: 180.5 °C
Boiling point	1330 °C	°C	Los Alamos: 1330 °C
Density	0.534 g/cm³	g/cm³
Electronegativity (Pauling)	0.98
Electron configuration	1s² 2s¹
Phase at 25 °C	solid

The standard atomic weight of this element is an interval in nature, from 6.938 to 6.997 Da; the value shown is IUPAC's conventional abridged value.

Safety

Lithium metal, the element on its own, carries the signal word Danger in PubChem’s GHS classification. Water, even the moisture on skin, reacts with it to give hydrogen gas that may ignite by itself and caustic lithium hydroxide, so contact burns skin and eyes. Once alight the metal is hard to put out, since it burns in nitrogen and carbon dioxide as well as in oxygen. The hazard belongs to those who handle the bare metal, and the PubChem Laboratory Chemical Safety Summary is the sheet for them.

Questions

Why is lithium used in batteries?

OpenStax gives four reasons a lithium-ion cell is popular: it can supply a large current, it weighs less than a comparable battery of another type, its voltage stays nearly constant while it discharges, and it loses its charge only slowly in storage. Los Alamos adds its own: a high electrochemical potential makes lithium a leading contender as an anode material. The US Geological Survey traces the growth in demand to electric vehicles, portable electronics, electric tools and grid storage.

Does lithium react with water?

Yes. Every alkali metal reacts with water to give hydrogen gas and a basic solution of its hydroxide, which OpenStax reads as the metal being easier to oxidise than hydrogen; for lithium the hydroxide is LiOH. Los Alamos and Jefferson Lab both call the reaction milder than sodium's, but the form of the metal matters: the safety summary has powdered lithium reacting explosively, shavings violently in hot water and vigorously in cold.

Why does lithium burn with a red flame?

Lithium and its salts colour a flame bright crimson, where sodium gives yellow and the rest of the group a pale violet, as OpenStax describes it. The colour is part of the element's emission spectrum, the set of wavelengths its atoms give out. Los Alamos adds a distinction: when the metal itself burns strongly, the flame turns a dazzling white rather than red.

Is lithium radioactive?

Natural lithium is not. It is a mix of two stable isotopes, lithium-6 at 7.59 per cent and lithium-7 at 92.41 per cent, the NIST figures in PubChem's record. The other lithium isotopes in that record are short-lived. The longest-lived with a stated half-life, lithium-8, lasts 838.7 milliseconds and decays by beta emission followed every time by an alpha particle; lithium-9 lasts 178.2 milliseconds, and about half its beta decays throw out a neutron as well.

Why does lithium's atomic weight have a range?

Atoms and ions of lithium's two stable isotopes differ slightly in physical and chemical behaviour, so physical, chemical and biological processes sort them, and natural materials end up with different isotope ratios and therefore different atomic weights. CIAAW's history in the same record shows the value moving over a century, 7.03 in 1902, 6.94 in 1911, 6.941 in 1969, until in 2009 a single number gave way to an interval.

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