Just my Opinion....
1.Dmitri Mendeleyev - Russian - Devised the Periodic table of elements. Predicted that several more elements would be discovered.
2.Antoine Lavoisier - French - Showed that air is a mixture of oxygen and nitrogen. Disproved the old Theory of phlogiston and determined the nature of combustion. Lavoisier wrote the first modern book on chemistry and explained the law of conservation of matter.
3.Henry Cavendish - English - Showed that water could be produced from two gases. Discovered hydrogen.
4. Amedeo Avogadro - Italian - First to distinguish molecules from atoms. Developed Avogadro's Constant (The number of particles of a substance in a mole). Studied the effect of combining volumes.
5. Jons Jakob Berzelius - Swedish - Developed the symbols for many of the chemicals. Calculated the atomic weights accurately of many of them and discovered Selenium, Silicon and Thorium.
6. John Dalton - English - Developed an atomic theory of matter and explained the laws of partial pressure.
7. Robert Boyle - Irish - Studied gases and showed how Pressure and volume at constant mass were indirectly proportional to one another.
8. Joseph-Louis Gay-Lussac and Jacques Charles - Both French - Studied gases. Showed that gas volume at constant pressure increases with Temperature.
9. Friederich Wöhler - German - Father of Organic Chemistry. He was the first chemist to synthesize an organic compound, Urea.
10. Carl Scheele - Swedish - Co-discover of oxygen with Joseph Priestley. Also discovered chlorine, manganese and molybdenum.
11. Marie Curie - Polish - Isolated radioactive elements radium and polonium.
12. Josiah Gibbs - American - Founder of Chemical Thermodynamics.
13. Jacobus van't Hoff - Dutch - Thermodynamicist. He was one of the earlier chemists to speak about the 3-D nature of molecules.
14. Frederick Sanger - English - Biochemist. Revealed the Amino sequence for insulin. Worked out methods for determining the molecular structure of nucleic acids. Two time Nobel Prize winner.
15. Humphry Davy - English - Showed the connection between electrochemistry and the elements. Discovered the elements Potassium, Sodium, Barium, Calcium and Magnesium amongst others.
16. Joseph Priestley - English - Oxygen co-discoverer. See Scheele.
17. Henri Le Chatelier - French - Developed principle that every change in a stable chemical equilibrium will result in a shift in the direction of the equilibrium to reduce the effects of the change.
18. Frederick Soddy - English - Introduced the isotope theory of elements.
19. Svante Arrhenius - Sweden - Established modern electrochemistry.
20. Germain Hess - Swiss/Russian - Introduced Hess's Law for determining the heat of reactions.
21.Wilhelm Ostwald - Latvian - Discovered Dilution law. Invented process to make nitric acid by oxidizing ammonia. He also developed a theory of colour.
22. Daniel Rutherford - Scottish - Discoverer of Nitrogen.
23. Friederich Kekulé - German - Organic Chemist. Described the ring structure of benzene.
24. Stanislao Cannizzaro - Italian - Established the use of Atomic weights in Chemical formulas and calculations.
25. Linus Pauling - American - Applied Quantum Theory to determine Chemical Structure (especially of proteins). Showed how electrons effect the formation of molecules.
26. Johannes Brønsted - Danish and Thomas Lowry - English - Independently introduced the Brønsted - Lowry definition of an acid as something that donates a proton and a base as something that accepts a proton.
27. Leo Baekland - Belgian/American - Father of the Plastics Industry.
28. William Ramsay - Scottish - Co-discovered Argon with Lord Rayleigh. Was first to identify, helium, neon, krypton and xenon.
29. Henri Moissan - French - Isolated fluorine. Invented the electric furnace. Discovered carborundum and produced artificial diamonds in a laboratory.
30. Theodore Richards - American - Performed extensive work on atomic weights to reveal the existence of isotopes.
31. Dorothy Hodgkin - English - Crystallographer. Used x-ray crystallography to reveal the structure of such molecules as penicillin and insulin.
32. Thomas Graham - Scottish - Developed Graham's Law of Diffusion. Founder of Colloidal Chemistry.
33. Fritz Haber - German - Invented the process to make ammonia from nitrogen in the air. Known as the Haber process. Invention allowed Germany to continue making explosives after World War I ban in spite of the blockade on the importation of nitrates.
34. Irving Langmuir - American. High Temperature chemist. Work lead to the development of the tungsten lamp. Also studied gases. Research in this field would have practical implications with respect to the use of atomic hydrogen in welding torches.
35. Peter Debye - Dutch - Worked as well on molecular structure. Pioneered x-ray powder photography.
36. Harold Urey - American - Isolated Heavy water and discovered deuterium.
37. Paul Flory - American - Leading figure in the field of Polymerization. Studied properties of plastics, ribbers and fibers.
38. William Perkin - English - Chemist noted for his work on dyes. Invented mauve.
39. George Washington Carver - American - Agricultural chemist. Research involved the synthesis of products from peanuts, sweet potatoes and soybeans.
40. François Raoult - French - Developed law which relates vapor pressure of a solution to the number of molecules of solute dissolved in it.