As discussed in an earlier answer 18th century Chemistry could call on such notable figures as Carl Wilhelm Scheele, Henry Cavendish, Antoine Lavoisier, Robert Boyle, Jacques Charles, Joseph Proust and Alessandro Volta. They set a high standard for Chemistry as a science. Lavoisier himself is often regarded as the father of Modern Chemistry.
The 19th century would be even more of a productive period. Englishman John Dalton (1808) , an earlier developer of a periodic table of elements, formulated his law of partial pressures to describe the relationship between components in a gas mixture. He also advanced the notion of multiple proportions.
John Dalton source: Leonardo Newtonic
Swede Jöns Jacob Berzelius (1808) started popularizing the modern use of symbols and notation that we use today.
Frenchman Joseph Louis Gay-Lussac (1805) showed that water is composed of two parts hydrogen to one part oxygen and added to the Gas law work carried out by Charles and Boyle in the previous century.
Italian Amedeo Avogadro (1811) proposed the Law that now bears his name in 1811, which states that equal volumes of gas under the same temperature and pressure contain the same number of particles. The Chemistry concept of the mole (the curse of every high school student), used to define the amount of a substance, follows from his work and was developed later by Johann Lofschmidt (1865).
Advances in Organic Chemistry were highlighted by Frederick Wohler’s synthesis of urea in 1825 (the birth of Organic Chemistry), and his additional endeavours together with Justus von Liebig on Isomers. Both chemists would stress the importance of functional groups in Organic Chemistry as well as the notion of chemical radicals (1832).
Germain Hess in 1840 provided an early version of the concept of Conservation of Energy and this was followed by other advances in physical chemistry around Absolute Zero (Lord Kelvin - 1848), Mass action (Cato Maximilian Goldberg and Peter Wage - 1864), Entropy (Ludwig Boltzmann - 1877), Chemical Equilibrium shifts (Henri Le Chatelier - 1884), Free Energy (Josiah Gibbs - 1876) and Kinetics (Jacobus van't Hoff- 1884 ).
Hess's Law (named after German Hess - useful in determining energy associated with chemical reactions) source: Socratic
Beer's Law (Named after August Beer - shows how the concentration of a solution is related to its light absorbance factor) source: Thoughtco.com
Models highlighting the nature of chemical bonding became more sophisticated in the 19th century. Friedrich August Kekulé (1857) showed how carbon has a tetravalent nature. Soon afterwards Alexandre-Émile Béguyer de Chancourtois (1862), John Newlands (1864) and Julius Lothar Meyer provided earlier versions of the Periodic table (1864). The German Meyer is particularly well known for his organization of the elements around valencies (bonding capacities).
In 1869 Russian Dmitri Mendeleev would publish the
First modern Periodic Table containing within it gaps of elements that were
awaiting discovery. Much of his efforts were aided by the earlier work of Stanislao Cannizzaro and his organization of the elements by atomic weight in 1860.
Dmitri Mendeleev source: New Scientist
Between 1894-98 Mendeleev’s missing
element hypothesis was given credence by William Ramsay’s discovery of the Noble gases.
Kekulé (1865) also showed how it was
possible that Benzene has a six ring carbon structure, ensuring its stability
as the base molecular for the Aromatic hydrocarbons. There was a more
sophisticated understanding of chemical reactions overall thanks to Alfred
Werner’s work on chemical coordination (1893). Svante Arrhenius ion theory (1883) also helped explain conductivity in electrolytes.
Chemical advances were often driven by the practical needs associated with the industrial revolution. Alexander Parkes' (1862) development of the one of the earliest polymers falls into this category as were the use of dyes (such as indigo) that formed the basis of the work of Adolf von Baeyer (1865) and William Perkin (mauve - 1856). Benjamin Stillman Jr. was a trendsetter for his ingenuity with respect to petroleum cracking (1855).
William Perkin source: sciencehistory.org However it is important to note that many chemical breakthroughs were driven by advances in Physics. JJ Thomson’s discovery of the electron in 1897 was one such event and this was followed by Ernest Rutherford and Pierre and Marie Curie’s work on radioactivity. The development of devices such as the Mass Spectrometer by Wilhelm Wien (1898) helped Chemists immensely.
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