---
title: "History of chemistry"
chunk: 9/20
source: "https://en.wikipedia.org/wiki/History_of_chemistry"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:59:28.102404+00:00"
instance: "kb-cron"
---

After Dalton published his atomic theory in 1808, certain of his central ideas were soon adopted by most chemists. However, uncertainty persisted for half a century about how atomic theory was to be configured and applied to concrete situations; chemists in different countries developed several different incompatible atomistic systems. A paper that suggested a way out of this difficult situation was published as early as 1811 by the Italian physicist Amedeo Avogadro (1776–1856), who hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules, from which it followed that relative molecular weights of any two gases are the same as the ratio of the densities of the two gases under the same conditions of temperature and pressure. Avogadro also reasoned that simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms. Thus Avogadro was able to overcome the difficulty that Dalton and others had encountered when Gay-Lussac reported that above 100 °C the volume of water vapor was twice the volume of the oxygen used to form it. According to Avogadro, the molecule of oxygen had split into two atoms in the course of forming water vapor.
Avogadro's hypothesis was neglected for half a century after it was first published. Many reasons for this neglect have been cited, including some theoretical problems, such as Jöns Jacob Berzelius's "dualism", which asserted that compounds are held together by the attraction of positive and negative electrical charges, making it inconceivable that a molecule composed of two electrically similar atoms—as in oxygen—could exist. An additional barrier to acceptance was the fact that many chemists were reluctant to adopt physical methods (such as vapour-density determinations) to solve their problems. By mid-century, however, some leading figures had begun to view the chaotic multiplicity of competing systems of atomic weights and molecular formulas as intolerable. Moreover, purely chemical evidence began to mount that suggested Avogadro's approach might be right after all. During the 1850s, younger chemists, such as Alexander Williamson in England, Charles Gerhardt and Charles-Adolphe Wurtz in France, and August Kekulé in Germany, began to advocate reforming theoretical chemistry to make it consistent with Avogadrian theory.

=== Wöhler, von Liebig, organic chemistry and the vitalism debate ===

In 1825, Friedrich Wöhler and Justus von Liebig performed the first confirmed discovery and explanation of isomers, earlier named by Berzelius. Working with cyanic acid and fulminic acid, they correctly deduced that isomerism was caused by differing arrangements of atoms within a molecular structure. In 1827, William Prout classified biomolecules into their modern groupings: carbohydrates, proteins and lipids. After the nature of combustion was settled, a dispute about vitalism and the essential distinction between organic and inorganic substances began. The vitalism question was revolutionized in 1828 when Friedrich Wöhler synthesized urea, thereby establishing that organic compounds could be produced from inorganic starting materials and disproving the theory of vitalism.
This opened a new research field in chemistry, and by the end of the 19th century, scientists were able to synthesize hundreds of organic compounds. The most important among them are mauve, magenta, and other synthetic dyes, as well as the widely used drug aspirin. The discovery of the artificial synthesis of urea contributed greatly to the theory of isomerism, as the empirical chemical formulas for urea and ammonium cyanate are identical (see Wöhler synthesis). In 1832, Friedrich Wöhler and Justus von Liebig discovered and explained functional groups and radicals in relation to organic chemistry, as well as first synthesizing benzaldehyde. Liebig, a German chemist, made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry, being considered one of its principal founders. Liebig is also considered the "father of the fertilizer industry" for his discovery of nitrogen as an essential plant nutrient, and his formulation of the Law of the Minimum which described the effect of individual nutrients on crops.

=== Vladimir Markovnikov ===

Vladimir Markovnikov, born in 1838, was a Russian scientist who did most of his work at Kazan University in Russia. At Kazan, he studied under Butlerov in a laboratory better known as "the cradle of Russian organic chemistry", after which he also studied chemistry in Germany for two years. Markovnikov's contributions to the fields of organic chemistry included the development of the eponymous Markovnikov's rule, which states that hydrogen halides when added to alkenes and alkynes would add in a way that hydrogens would bond to the side of the carbon with the most hydrogen substituents. Products in chemistry that follow this rule are considered Markovnikov products and those that did not are considered anti-Markovnikov products. Markovnikov's rule was an early example of regioselectivity in organic synthesis and the modern understanding of it continues to be important in the chemical industry, where catalysts have been developed to produce anti-Markovnikov products. A significant aspect of Markovnikov's rule is that it explains reactivity based on the structural arrangement of atoms, as many chemists at the time did not consider chemical formulas as representing physical arrangement of atoms (see also radical theory).