From the flames that smelted bronze to molecules designed by AI
Chemistry began as craft before it became theory. People extracted metals from ore and made alloys, glass and dyes, but no one explained why any of it worked.
Drawing metal out of stone.
People learned that heating ores such as malachite in a charcoal fire made copper run out. It is a reduction reaction in which carbon strips oxygen from the ore, but another 6,000 years would pass before anyone understood the principle.
Mix copper with tin and it gets harder.
Bronze, copper alloyed with tin, is far harder than pure copper. It transformed weapons and tools and gave its name to an age. It was alloying learned by experience: the proportions change the properties.
Preserving a body for thousands of years.
The Egyptians made mummies by drying bodies with natron, a natural sodium carbonate, and treating them with resins and spices. In the same era, Mesopotamia and Egypt produced glass, glazes, pigments and perfumes. All of it was chemistry built on experience.
Higher temperatures, a more common metal.
Iron needs much higher temperatures than copper and was harder to work, but its ore is plentiful, and once smelting spread it became the material for tools and weapons. People also learned by experience that adding a little carbon makes harder steel.
In Greece, by contrast, people speculated about the nature of matter without experiments. The four-element theory established in this period became the theoretical basis of alchemy for 2,000 years.
Earth, water, air and fire.
Empedocles argued that all matter in the world is four elements mixed and separated by the forces of Love and Strife.
Grains that cannot be divided further.
Leucippus and Democritus argued that all matter consists of indivisible atoms and empty space. Overshadowed by Aristotle's authority, the idea slept for 2,000 years until Dalton revived it.
Change the qualities, and the element changes.
Aristotle explained the four elements as combinations of the qualities hot and cold, dry and wet. The idea that changing these qualities could turn one element into another became the theoretical basis for alchemy's attempts to turn lead into gold.
Alchemy is often dismissed as superstition, but it developed the techniques and apparatus, such as distillation and crystallization, that make it chemistry's direct ancestor. It began in Alexandria and passed through the Islamic world to Europe, while in China the search for immortality produced gunpowder.
Greek philosophy meets Egyptian craft.
In Alexandria, Greek element theory met Egyptian metalworking and dyeing, and alchemy was born. Zosimos of Panopolis was an early alchemist who left written records of distillation apparatus and experimental procedures.
The name of Islamic alchemy.
A vast body of writings attributed to Jabir dealt systematically with techniques such as distillation, crystallization and sublimation. Many scholars think the texts were written by several authors and gathered under his name. Alcohol, alkali and alchemy all come from Arabic.
Classifying substances and organizing lab equipment.
Al-Razi, a Persian physician and alchemist, classified substances as mineral, vegetable or animal and carefully recorded laboratory apparatus and procedures. He treated alchemy as experimental technique rather than mysticism.
An explosive found while searching for an elixir of life.
Chinese alchemy sought an elixir of immortality more than gold, and along the way people found that saltpeter, sulfur and charcoal mixed together burn violently. The Song dynasty military encyclopedia Wujing Zongyao contains the world's first written formula for gunpowder.
Acids that dissolve metal.
European alchemists of the 13th and 14th centuries produced strong acids such as nitric and sulfuric acid, and found that aqua regia, a mixture of nitric and hydrochloric acid, could dissolve even gold. These records survive in writings attributed to "pseudo-Geber," who borrowed Jabir's name.
Alchemy's goal shifted from making gold to making medicines and improving mining, and the first chemistry textbook appeared. Boyle proposed defining elements by experiment.
"The dose makes the poison."
Paracelsus turned alchemy from making gold toward making medicine and used mineral remedies such as mercury and antimony. His idea that the same substance can be a medicine or a poison depending on the amount became the starting point of toxicology.
An encyclopedia of mining and smelting.
Georgius Agricola of Germany documented mining, ore assaying and smelting, illustrated with hundreds of woodcuts. It remained the standard textbook of mining and metallurgy for 200 years.
The first chemistry textbook.
Libavius stripped away the mysticism and published a textbook that systematically organized chemical knowledge, experimental procedures and even laboratory design.
An element is a substance experiments can break down no further.
Boyle criticized the four-element theory and the vague explanations of alchemy, and proposed defining elements by experiment. He is the same Boyle of Boyle's law, which says a gas's pressure and volume are inversely proportional.
A glowing substance from urine.
Hennig Brand, a German alchemist trying to make gold, boiled down urine and obtained a substance that glowed in the dark. It was the first element whose discoverer is known.
The phlogiston theory of combustion dominated chemistry, and it began to emerge that air is not a single substance but a mixture of several gases.
Something escapes when things burn.
Stahl explained that a substance called "phlogiston" escapes when something burns. Since burning wood leaves only ash, it sounded plausible. The problem was that metals actually get heavier when burned, which led to contortions such as giving phlogiston negative mass.
A "fixed air" unlike ordinary air.
Joseph Black showed quantitatively that the gas released by heating limestone differs from ordinary air and called it "fixed air." It was carbon dioxide. He is the same Black who discovered latent heat.
Inflammable air.
Cavendish isolated a very light, highly flammable gas produced by pouring acid on metal: hydrogen. He is the same Cavendish who later weighed the Earth.
With a precise balance, Lavoisier turned chemistry into a quantitative science. He was to chemistry what Newton was to physics.
Dephlogisticated air.
Scheele in Sweden and Priestley in England each discovered a new gas that made things burn vigorously. But Priestley, a believer in phlogiston, called it "dephlogisticated air." They saw the same gas and read it through different theories.
Burning is combining with oxygen.
By weighing reactions precisely in sealed vessels before and after, Lavoisier established the law of conservation of mass and showed that combustion is combination with oxygen. Why metals get heavier when burned was explained, and the phlogiston theory collapsed.
Splitting it into hydrogen and oxygen, then putting it back together.
Lavoisier broke water down into hydrogen and oxygen and synthesized it again, proving that water, considered an element for 2,000 years, is a compound.
Names that tell you what's inside.
Lavoisier and his colleagues created a systematic nomenclature in which a name such as "sulfuric acid" or "iron oxide" reveals the composition. Before that, chemists used alchemical names like "oil of vitriol" and "salt of Jupiter."
A list of 33 elements.
In a textbook that set out the new chemistry systematically, Lavoisier presented a list of 33 elements, though light and heat (caloric) were still on it. His wife, Marie-Anne Lavoisier, who handled experiments and illustrations, was an important partner in this revolution.
"A hundred years may not produce another head like it."
Because he had invested in a tax-collecting firm, Lavoisier was guillotined during the Reign of Terror. Lagrange is said to have lamented that it took only a moment to cut off that head, and a hundred years might not produce another like it.
The same compound always comes in the same ratio.
Proust showed that, however it is made, a given compound always contains its elements in the same proportions by mass. It was a clue that would bring atomic theory back.
Dalton revived atomic theory quantitatively, and the voltaic pile became a new tool for breaking substances apart with electricity. Organic substances, thought to be made only by living things, began to be synthesized in the laboratory.
Within weeks of the battery's invention.
As soon as the voltaic pile was announced, Nicholson and Carlisle used an electric current to split water into hydrogen and oxygen. Electricity became a powerful tool for driving chemical reactions.
Every element has atoms of its own weight.
Dalton proposed that each element has atoms with a characteristic weight and that compounds are atoms combined in simple whole-number ratios, and he made the first table of atomic weights. Democritus's atom returned after 2,000 years as a quantitative scientific theory.
Pulling new elements out with electricity.
Humphry Davy used a powerful current to decompose potassium hydroxide and sodium hydroxide, isolating potassium and sodium for the first time. Over the next few years he found several more elements, including calcium and magnesium, the same way.
Equal volumes of gas hold equal numbers of molecules.
When Gay-Lussac found that gases react in simple whole-number ratios by volume, Avogadro explained it with the hypothesis that equal volumes of gas at the same temperature and pressure contain the same number of molecules. The hypothesis was ignored for nearly 50 years.
H, O, Fe.
Berzelius introduced symbols for the elements based on the first letters of their Latin names. Replacing alchemy's pictorial signs, they became the basis of today's chemical formulas. He also contributed greatly to precise measurement of atomic weights.
A university where students do the experiments.
At the University of Giessen in Germany, Justus von Liebig introduced laboratory-centered chemistry teaching in which students learned by doing experiments systematically themselves. Students came from all over the world, laying the foundation for German chemistry's world leadership.
A substance of life, without a life force.
Vitalism held that substances made by living things required a special "vital force." Wöhler synthesized urea, a component of urine, from the inorganic compound ammonium cyanate. Vitalism did not collapse overnight, but this became the symbolic starting point of organic chemistry.
Does electricity come in units?
Faraday, who had been Davy's assistant, established that the amount of substance produced by electrolysis is proportional to the electric charge passed. It was the first hint that electricity exists in fixed units, and he coined terms such as electrolyte, electrode and ion.
Crystals shaped like left and right hands.
Pasteur discovered that crystals of tartaric acid come in two mirror-image forms, and that solutions of each rotate light in opposite directions. It was the discovery of chirality: molecules have "handedness."
It became clear that the arrangement of atoms matters, not just their kinds and numbers, and synthetic dyes launched the chemical industry. Mendeleev's periodic table brought order to the world of the elements.
A purple found while trying to make a malaria drug.
Eighteen-year-old William Perkin was trying to synthesize the malaria drug quinine from coal tar when he accidentally made a purple synthetic dye. Its huge success created the synthetic dye industry, and companies such as BASF and Bayer grew up, especially in Germany, later expanding into pharmaceuticals.
Carbon has four hands.
Kekulé proposed that carbon atoms form four bonds and link to one another in chains. The same year Couper independently reached a similar idea, and the structural formula, which draws bonds between atoms as lines, was born.
Sorting out the chaos of atomic weights.
With every chemist using different atomic weights and formulas, the first international chemistry conference was held. Italy's Cannizzaro revived the forgotten hypothesis of Avogadro, atomic weights were put in order, and Mendeleev, who attended, was deeply influenced.
A snake biting its own tail.
Kekulé proposed that benzene's six carbon atoms are joined in a ring. The story that it came to him in a dream of a snake biting its tail is famous, but since he told it himself years later, its truth is uncertain.
An element discovered on the Sun before the Earth.
After Bunsen and Kirchhoff's spectroscopy revealed cesium and rubidium, an unknown yellow line was seen in the Sun's spectrum during an eclipse. It was named helium, after the Greek word for the Sun, and was found on Earth only 27 years later.
Predicting elements that did not yet exist.
Mendeleev made a table showing that when the elements are arranged by atomic weight, their properties repeat periodically. Lothar Meyer independently arrived at a similar table at almost the same time. Mendeleev's genius was to leave gaps where the pattern didn't fit and predict the properties of elements not yet discovered. No one knew why periodicity arose.
Carbon's four hands point to the corners of a tetrahedron.
Van 't Hoff and Le Bel each explained that carbon's four bonds point toward the corners of a tetrahedron. The mystery of Pasteur's mirror-image molecules was solved, and stereochemistry, thinking of molecules in three dimensions, began.
The prediction was right.
The element Mendeleev had called "eka-aluminium," predicting its properties, was discovered as gallium. Scandium (1879) and germanium (1886) followed, with properties close to his predictions. It was a moment like the discovery of Neptune for Newtonian mechanics.
Calculating whether a reaction will happen on its own.
America's Josiah Willard Gibbs used the concept of free energy to establish how to predict whether chemical reactions and phase changes occur spontaneously. Published in an obscure journal, his papers were appreciated only belatedly in Europe.
Salt splits into ions in water.
Arrhenius proposed that substances like salt split into charged ions when dissolved in water, and in 1889 introduced activation energy, the energy barrier a reaction must cross. Together with van 't Hoff's theories of equilibrium and osmotic pressure and Ostwald's work on catalysis, physical chemistry became a field of its own.
A new column on the periodic table.
Rayleigh and Ramsay tracked down a tiny discrepancy, nitrogen from air was slightly heavier than nitrogen made chemically, and discovered argon. Ramsay went on to find helium, neon, krypton and xenon, adding an entirely new group to the periodic table.
A drug made by a dye company.
Felix Hoffmann at Bayer improved on salicylic acid, derived from a compound in willow bark, and synthesized acetylsalicylic acid, which was gentler on the stomach. It symbolized the transformation of dye companies into drug companies.
The atomic structure and quantum mechanics revealed by physics answered chemistry's old questions: why periodicity arises and why atoms bond. At the same time chemistry sustained and threatened civilization with fertilizers, poison gas and plastics.
Bread from air, and explosives too.
Haber developed a way to synthesize ammonia from nitrogen in the air and hydrogen, and Bosch turned it into a large-scale process in 1913. Nitrogen fertilizer now feeds a large share of the world's population. But the same technology let Germany produce explosives in World War I, and Haber personally directed the development of poison gas.
The true order of the elements.
By measuring the frequencies of X-rays each element emits, Moseley showed that the true order of the elements is not atomic weight but atomic number, the charge of the nucleus. Several anomalies in the periodic table were resolved, and the number of gaps became exactly known. Two years later, at 27, he was killed in World War I.
A covalent bond is a shared pair of electrons.
Gilbert Lewis proposed that atoms bond by sharing a pair of electrons, and introduced structures that draw electrons as dots around atoms. They are still the first diagrams students learn in chemistry class.
Rubber and cellulose are giant chains.
Staudinger argued that rubber and cellulose are not clumps of small molecules but giant molecules of thousands of atoms joined by covalent bonds. He met resistance for years, but his idea became the foundation of polymer chemistry.
Calculating the bond in a hydrogen molecule.
Using the brand-new quantum mechanics, Heitler and London calculated for the first time why two hydrogen atoms bond. In 1929 Dirac remarked, in effect, that the physical laws underlying most of chemistry were now known; the only problem was that the equations were too complicated to solve.
Hybrid orbitals and electronegativity.
Linus Pauling used hybrid orbitals and electronegativity to turn the quantum theory of bonding into something chemists could use, while Mulliken developed molecular orbital theory, with orbitals spread across the whole molecule. Pauling's The Nature of the Chemical Bond became one of the most cited science books of the 20th century.
A fiber made from coal, water and air.
Building on macromolecule theory, Wallace Carothers at DuPont created nylon, the first fully synthetic fiber. Used in everything from stockings to parachutes, it opened the age of plastics and synthetic materials.
Nuclear fission, discovered by a chemist.
The chemist Otto Hahn used chemical analysis to confirm that light barium appears in uranium hit by neutrons, and Meitner and Frisch explained it as nuclear fission. In the 1940s McMillan and Seaborg created elements heavier than uranium, such as neptunium and plutonium, extending the periodic table.
A magnet that sees inside molecules.
Bloch and Purcell each observed nuclear magnetic resonance: atomic nuclei in a strong magnetic field absorb radio waves at specific frequencies. NMR became chemists' key tool for working out molecular structures and led to medical MRI.
Chemistry looked directly at the molecules of life and began to recognize its effects on the planet. Molecules were calculated by computer, and new forms of carbon were discovered.
The structure of life's molecule, and the chemical origin of life.
Watson and Crick revealed that DNA is a double helix of two twisted strands. The decisive evidence was Rosalind Franklin's X-ray diffraction photograph. The same year Miller and Urey sent electric sparks through a flask imitating the early Earth and showed that amino acids form on their own.
The first protein seen with X-rays.
Using X-ray crystallography, Kendrew revealed for the first time the 3D structure of myoglobin, a muscle protein, and Perutz solved hemoglobin. In the same period Dorothy Hodgkin determined the structures of penicillin and vitamin B12.
Pesticides silence the birds.
Rachel Carson exposed the harm that synthetic pesticides such as DDT do to ecosystems and people. The book launched the environmental movement and led to regulation of chemicals.
Spray-can gases punch a hole in the sky.
Molina and Rowland warned that chlorofluorocarbons (CFCs), used in refrigerators and spray cans, could rise to the stratosphere and destroy the ozone layer. After the Antarctic ozone hole was observed in 1985, the world cut CFC production under the 1987 Montreal Protocol, often called the most successful international environmental agreement.
A carbon molecule shaped like a soccer ball.
Kroto, Curl and Smalley discovered a molecule of 60 carbon atoms joined in the shape of a soccer ball and named it after Buckminster Fuller, the architect who designed domes of similar structure. A new form of carbon beyond diamond and graphite opened the door to nanomaterials research.
Portable energy you can recharge.
Building on the work of Goodenough, Whittingham and Yoshino, Sony commercialized the lithium-ion battery. The battery that made laptops, smartphones and electric cars possible won the 2019 Nobel Prize in Chemistry.
Solving Dirac's equations by computer.
When Walter Kohn, creator of density functional theory, and John Pople, who developed molecular calculation software, received the Nobel Prize in Chemistry, computational chemistry, predicting molecular properties by computer without experiments, entered the mainstream. The same year Anastas and Warner set out the "12 Principles of Green Chemistry" for using and producing fewer hazardous substances from the start.
Chemistry blends ever more deeply with biology, materials science and computer science. It edits genes, snaps molecules together like Lego and designs proteins with AI.
A single layer of atoms peeled off with sticky tape.
Geim and Novoselov isolated graphene, a sheet of carbon one atom thick, with a simple trick: pressing sticky tape onto graphite and peeling it off. The thinnest material known, yet strong and highly conductive, it earned them the 2010 Nobel Prize in Physics.
Editing DNA with a bacterial immune system.
Doudna and Charpentier showed that CRISPR-Cas9, the system bacteria use to fend off viruses, could be turned into a tool for cutting DNA at any chosen location. They received the 2020 Nobel Prize in Chemistry.
Nihonium, moscovium, tennessine, oganesson.
With names confirmed for elements 113, 115, 117 and 118, the seventh row of the periodic table was completely filled. Only a handful of atoms of these elements have been made in particle accelerators, and they decay almost instantly. Element 118, oganesson, was named after Yuri Oganessian, who was alive when the name was given.
Snapping molecules together like Lego.
Sharpless and Meldal developed click reactions that join chosen molecular pieces quickly and reliably, and Bertozzi extended them to bioorthogonal chemistry that works even inside living cells.
Computers predict and design proteins.
Hassabis and Jumper, who created AlphaFold to predict protein structures, and Baker, who designed new proteins computationally, received the Nobel Prize in Chemistry. AI had entered the territory of what Dirac called equations too complex to solve.
Porous buildings made of molecules.
Kitagawa, Robson and Yaghi received the Nobel Prize in Chemistry for developing metal–organic frameworks, crystal structures that link metal ions and organic molecules around vast internal spaces. Applications under study range from harvesting water from desert air to capturing carbon dioxide.