Chemistry · Fundamentals of chemistry · Year 1

From alchemy to the periodic law

Alchemists thought they had “turned” iron into copper — what had really changed on the scales?

The situation

In a cell of a madrasa in Bukhara, an alchemist dips an iron nail into a solution of blue vitriol — the nail turns red and “becomes copper”. Eight centuries later in Paris, Lavoisier heats tin in a sealed retort and weighs it on a balance; in Manchester, Dalton measures the proportions of gases; and in St Petersburg, Mendeleev lays out cards on a table and leaves gaps for elements that nobody has yet seen. Why did the alchemists’ dream not come true, how did chemistry become an exact science, and which experiments opened the way?

Topic

History of chemistry: from alchemy to the periodic law. Four rooms — four eras. An alembic in a Bukhara madrasa cell (al-Razi's distillation apparatus, Ibn Sina's rose water, al-Biruni's balance for relative densities of minerals and metals)…

Key ideas

Conservation of mass
Multiple and volume ratios
The periodic law and predictions

Formulas

Fe + Cu^{2 +} \overset{}{\to} Fe^{2 +} + Cu

Iron displaces copper from blue vitriol — this is not transmutation but displacement: the copper comes from the solution.

\sum m_{init.} = \sum m_{fin.}

The law of conservation of mass (Lomonosov 1748/1756, Lavoisier 1774–1789): in a closed vessel the mass does not change.

2 H_{2} + O_{2} \overset{}{\to} 2 H_{2} O V (H_{2}) : V (O_{2}) : V (H_{2} O) = 2 : 1 : 2

Gay-Lussac’s law of combining volumes; Avogadro (1811): equal volumes contain equal numbers of molecules.

M = 2 D_{H_{2}}, A (El) = \min m {(El)}_{1 mol}

Cannizzaro’s method: the molar mass from the vapour density, the atomic weight as the smallest mass of the element in 1 mol of its compounds.

A (eka-silicon) \approx \frac{1}{4} (A_{Si} + A_{Sn} + A_{eka-Al} + A_{As})

Mendeleev’s “atomic analogy” method: the properties of an unknown element are close to the average of its neighbours.

Theory

The beginnings of chemistry: craft practice, atomism, alchemy

Chemistry began with practical craft: in the Stone Age and Neolithic, fire and pottery (firing clay), then the copper, bronze (Cu + Sn) and iron ages — each of which required smelting metal from ore; in the 2nd millennium BCE glass vessels were made in Mesopotamia and Egypt. In the 5th century BCE Leucippus and Democritus held that matter consists of indivisible particles — atoms; Aristotle developed the idea of four elements (earth, water, air, fire) and four qualities: by exchanging qualities, one substance could be turned into another. In the Hellenistic period, in Alexandria, this idea merged with the experience of craftsmen, and alchemy was born. The chief aim of Greco-Egyptian alchemy was transmutation — turning base metals into gold. Its representatives include Bolus of Mendes (around the 2nd century BCE), Mary the Jewess (the water bath and distillation apparatus are attributed to her) and Zosimos of Panopolis (c. 300 CE). Along this path much practical knowledge was gathered about distillation, sublimation, crystallisation, alloys and dyes.

Eastern alchemy and the scholars of Central Asia

In the 8th–11th centuries Greek works were translated into Arabic (the “House of Wisdom” in Baghdad), and alchemy began to rely on experiment. The works linked with the name of Jabir ibn Hayyan (c. 721–813; historians dispute their authorship) set out the sulfur–mercury theory: all metals form underground from mercury and sulfur, depending on their purity and proportion — so, by changing the proportion, gold could be made. Al-Kindi (c. 801–873) wrote about perfumes and distillation and rejected the claims of making gold. Abu Bakr al-Razi (865–925), in the “Book of Secrets”, divided substances into mineral, plant and animal, and the minerals into “spirits” (mercury, sal ammoniac, sulfur, arsenic sulfides), metals, stones, vitriols, borates and salts, and described laboratory apparatus — the alembic, cauldron, crucible and mortar. Abu Nasr al-Farabi (c. 872–950) defended the possibility of alchemy. Abu Rayhan al-Biruni (973–1048), in “Mineralogy”, measured the relative densities of metals and precious stones (his method is in the “History of physics: al-Biruni, Ulugh Beg” experiment). Abu Ali ibn Sina (980–1037), in “The Book of Healing”, wrote that alchemists cannot change the kind of a metal, only dye it to look like another. The algebra of al-Khwarizmi and the astronomy of al-Farghani show this era’s tradition of exact calculation. The apparatus and the dates of the scholars are also covered in the “The chemistry lab and safety” experiment.

Western alchemy, technical chemistry and iatrochemistry

In the 12th–13th centuries Arabic works were translated into Latin. Albertus Magnus (c. 1200–1280) wrote about minerals, and Roger Bacon (c. 1219–1292) regarded experiment as the basis of science; many alchemical treatises circulated under the names of Arnaldus de Villanova and Raymond Lull. In the Latin texts of “Pseudo-Geber” (late 13th century) there are descriptions of mineral acids — “strong water” (nitric acid) and aqua regia. Works under the name of “Basil Valentine” (early 1600s) describe antimony compounds. In the 16th–17th centuries technical chemistry flourished: V. Biringuccio’s “Pirotechnia” (1540) and G. Agricola’s “On Metals” (1556) were handbooks of ores and metallurgy; there were Venetian glass, porcelain (Meissen in Europe, 1708–1710), ceramics, salts, paper, and later the production of soda from table salt (N. Leblanc, 1791). Iatrochemistry (Paracelsus, 1493–1541) directed chemistry towards preparing medicines: the three principles — sulfur, mercury, salt; Van Helmont introduced the word “gas”. In this period of convergence practical knowledge and theory came closer together.

Scientific chemistry: Boyle, phlogiston, pneumatic chemistry, Lavoisier and Lomonosov

In “The Sceptical Chemist” (1661) R. Boyle criticised, by experiment, Aristotle’s four elements and Paracelsus’s three principles; he understood an element as a simple, “unmingled” body not made up of other bodies, and linked the corpuscular (atomistic) view with experiment. The practical definition of an element — a substance that cannot be broken down by analysis — is Lavoisier’s (1789). G. Stahl (building on the idea of J. Becher) created the phlogiston theory: when a combustible substance burns, “phlogiston” escapes from it. But a metal gets heavier when it is burnt! The pneumatic trough (S. Hales, 1727) made it possible to collect gases over water: J. Black — CO₂ (“fixed air”, 1754–1756), H. Cavendish — H₂ (“inflammable air”, 1766), D. Rutherford — N₂ (1772), J. Priestley — O₂ (1774, by heating HgO with a lens; C. Scheele had obtained it slightly earlier, published 1777). A. Lavoisier (1743–1794) heated tin in a sealed retort and showed that when weighed unopened the mass does not change, and when it is opened air rushes in and the mass increases; in the 12-day mercury experiment he proved that about 1/6 of the air is absorbed and a red calx forms, and that when the calx is heated the same gas returns — the oxygen theory of combustion. He created chemical nomenclature (1787) and the “Elementary Treatise on Chemistry” (1789). M. V. Lomonosov (1711–1765) built a chemical laboratory in St Petersburg (1748), set out the conservation of matter and motion in a letter to Euler (1748), and in 1756 burnt a metal in a closed vessel and observed that the mass did not change. Safety: mercury and its vapour, and the SO₂ released when mercury sulfide is heated, are poisonous — these experiments are only a historical reconstruction and are not done in a school laboratory.

Quantitative laws and atomic–molecular theory

J. Richter (1792–1794) found that substances react in exact equivalent proportions (“stoichiometry”); J. Proust (1799) — the law of definite proportions. J. Dalton (1803–1808): each element consists of atoms with their own weight; if the same elements form several compounds, the masses of the second element per unit mass of the first are in ratios of small whole numbers (multiple proportions: 1 : 2 : 3 : 4 : 5 for N₂O : NO : N₂O₃ : NO₂ : N₂O₅); he drew up the first table of atomic weights and circular symbols (taking water to be HO, he got O = 7). J. Gay-Lussac (1808) — gases react in small whole-number ratios of volumes; A. Avogadro (1811) explained this with molecules: equal volumes contain equal numbers of molecules, and H₂ and O₂ are diatomic. J. Berzelius introduced letter symbols (1813–1814) and accurate atomic weights, and developed chemical analysis. Electrochemistry: the voltaic pile of A. Volta (1800); H. Davy isolated K and Na by electrolysis (1807), then Ca, Mg, Ba and Sr (1808); M. Faraday introduced the laws of electrolysis (1833–1834, $m = M I t / (z F)$ ) and the terms “electrode, anode, cathode, ion” (the “Electrolysis, Faraday's laws” experiment). Avogadro’s idea was revived by S. Cannizzaro (1858); the Karlsruhe Congress (1860) ended without a decision, but Cannizzaro’s pamphlet distributed there led in the following years to a single system of atomic weights.

Organic chemistry, the periodic law, atomic structure, the 20th–21st centuries and Uzbekistan

Vitalism (only a living organism can make organic matter) was shaken by F. Wöhler’s synthesis of urea (1828); the syntheses of H. Kolbe (ethanoic acid, 1845), N. N. Zinin (aniline, 1842) and M. Berthelot refuted it completely. After the theories of radicals and types, A. Kekulé and A. Couper (1857–1858) established the tetravalence of carbon, A. M. Butlerov (1861) created the theory of chemical structure, and van ’t Hoff and Le Bel (1874) — stereochemistry. The periodic law: J. Döbereiner’s triads (1829), J. Newlands’s “law of octaves” (1865), L. Meyer’s tables (1864, 1870), D. I. Mendeleev’s table (1869) and “Principles of Chemistry” (1868–1871): he left gaps and predicted eka-boron, eka-aluminium and eka-silicon — Ga (1875), Sc (1879) and Ge (1886) were discovered; for the pair Te and I he put properties ahead of mass order. Atomic structure: radioactivity (A. Becquerel 1896, the Curies 1898), the electron and Thomson’s model (1897, 1904), Rutherford’s nucleus (1911), Bohr’s model, F. Soddy’s isotopes and H. Moseley’s law (1913), the bonding theories of Lewis and Kossel (1916), then the valence-bond and molecular-orbital methods; quantum mechanics (Planck 1900, Einstein 1905, de Broglie 1924, Heisenberg, Schrödinger 1926, Dirac 1928) gave birth to quantum chemistry. The 20th century: X-ray structure analysis, chromatography (M. Tswett), NMR (1946), gas chromatography–mass spectrometry, “labelled atoms” (G. Hevesy), polymers (H. Staudinger) and bioorganic chemistry. The 21st century: supramolecular chemistry, nanomaterials, photocatalysis, femtochemistry, biochemistry and “chemical medicine”; the benefits of pesticides, herbicides and fungicides together with their danger to the environment. In Uzbekistan: Academician S. Yu. Yunusov (1909–1995) founded the Institute of the Chemistry of Plant Substances (1956) — more than 800 alkaloids were isolated; O. S. Sodiqov (1913–1987) was President of the Academy of Sciences, and the Institute of Bioorganic Chemistry bears his name; industry: Chirchik (Maxam-Chirchik), Navoiyazot and Fergana Azot — nitrogen fertilisers, the Almalyk and Navoi Mining and Metallurgical Combines, and the Shurtan and Ustyurt gas chemical complexes. About the model: the scene is a reconstruction; the historical numbers are from sources, the reaction rates are shortened in time, and the masses are calculated with today’s atomic masses.

Did you know?

The drawings of apparatus in Lavoisier’s “Elementary Treatise on Chemistry” (1789) — 13 engravings — were drawn by his wife, Marie-Anne Paulze-Lavoisier; she also translated the works of English chemists into French.
Germanium was isolated in 1886 by C. Winkler from the mineral argyrodite and named in honour of Germany; its atomic weight (72.6) and density (5.32 g/cm³) turned out to be very close to the 72 and 5.5 that Mendeleev had predicted in 1871 for “eka-silicon”.

Inside the experiment

The experiment starts from a real-life situation: you predict the result, change the controls, run the experiment and draw a conclusion. Inside are missions, theory, a quiz and a guided tour in which the camera moves and explains the key points.