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469 BCE
Greece's Democritus
Democritus hypothesized that atoms are indivisible, exactly alike, make up all matter, and are eternal. He based these hypotheses from his learning and traveling in his life. -
384 BCE
Greece's Aristotle
Aristotle hypothesized that all matter was made up of some basic particles and how elements are transformed. He also created a criteria of purity to describe elements. -
721
Persia's Abu Musa Jabir ibn Hayyan
The Father of Arabic Chemistry created a system of quantitative analysis of substances in the 8th century. This system is called the method of balance. He also discovered sulfuric acid and developed the technique of distillation. -
1245
Germany's Albertus Magnus
Seperated the natural sciences from religion? He found out that movable bodies can be sperated into three groups: de mineralibus, de vegetabilibus, and de animalibus. -
1436
Printing Press
The printing press was invented during the Renaissance. It has helped with mass producing the papers of discoveries of scientists. -
Ireland's Robert Boyle
In 1662, Boyle experimented and calculated his results leading to a discovery. This discovery was named Boyle's law where the volume of the gas varies inversely with pressure. -
France's Lavoisier
Through experiments, Lavoisier established the law of conservation of mass. In his experiments, he used weights of elements in order to make sure his belief wasn't violated. He also believed that mass is neither created or destroyed. -
England's Henry Cavendish
Realized that there was something heavier than common air. He recognize hydrogen gas as a distinct substance. He had to calculate air and hydrogen density, as well as other gases. He made the first accurate measurement of density. -
England's Henry Cavendish
He was the first to describe the composition of water, which was hydrogen and oxygen. He did this by measuring heats of fusion and evaporation as well as specific heats and those of the mixing of solutions in water. As well as measuring freezing points of various solutions showed the existence of compositions that yield maximum and minimum freezing points. -
England's Dalton
Dalton's Atomic Theory consists of statements about particles: all matter is made of particles; particles are identical in mass and properties; compounds are combos of different atoms; and chemical reactions cannot create or destroy particles. -
Italy's Amedeo Avogadro
Avogadro's law: Is when equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules. 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. Simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms
His hypothesis was neglected, because of many problems, mainly theoretical. -
Mendeleev
Mendeleev found the expansions of liquids and defined critical temperatures of gases. He also found the formula for the expansion of liquids with heat. He defined critical temperature of a substance as the temperature at which cohesion and heat of vaporization become equal to zero and the liquid changes to vapor, irrespective of the pressure and volume. -
Period: to
Mendeleev
Mendeleev wrote the Principles of Chemistry. He did this because while he was teaching inorganic chemistry there wasn't a textbook that was meeting his needs. The book became a classic and ran through editing many times, as well was translating many times. The book is split into two volumes. -
Mendeleev
While Mendeleev was correcting and improving the periodic table he discovered the Periodic Law. Which is when elements are ordered according to their atomic weights, but certain properties of elements repeat periodically. The periodic table organized all known elements according to their atomic weights and was a visual representation of the periodic law. -
Russia's Dimitri Mendeleev
Improved the periodic table, by correctly calculating incorrect masses, arranged by atomic number, not by atomic mass. He also correctly predicted unknown elements, and their places in the table, by leaving gaps in the table, of which elements weren’t found yet, and predicted some properties and compounds of unknown elements. -
Scotland's William Ramsay
He discovered agron, while he was trying to find something that was heavier than air. Agron then was used in light bulbs. While trying to find agron in uranium-bearing mineral, he found helium. Helium was only found on the sun, until he discovered it. Helium was then used to inflate aircrafts, to make them lighter than air. He then found out that there was another group to the periodic table of elements, the noble gases. He co-workers then added neon, krypton, and xenon from the atmosphere. -
England's JJ Thomson
Thomas created better equipment in order to study cathode rays. Because of this, he was able to calculate the ratio of the electrical charge to the mass of particles. -
New Zealand's Rutherford
Rutherford's studies on ion-producing radiations was based on a discovery and led to a discovery. His experiments led to the discovery of alpha and beta particles. He also developed the categories of radioactive elements called the decay series. -
Poland's Marie Curie
Discovered polonium and radium -
England's JJ Thomson
Thomson started another experiment where he channeled a stream of ionized neon through a magnetic and an electrical field. He used deflection techniques to measure the charge to mass ratio. -
Denmark's Niels Bohr
He proposed that the atom was contained of neutrons and protons on the center, while the electrons orbited around them. The electrons have a fixed distance from the nucleus. If an electron received more energy it could move up a step, and if it lost energy, it went down a step. -
Austria's Lise Meitner
Meitner and Otto Hahn studied radioactivity, leading to the discovery of protactinium. -
Germany's Heisenberg
Heisenberg studied and observed the spectrum of intensities of the electron taken as an anharmonic oscillator. His studies led to the development of the Uncertainty Principle and the Theory of Quantum Mechanics. -
England's Irene Joliot-Curie
Her and her husband bombard a thin piece of aluminum with alpha particles, a new kind of radiation was discovered that left traces of apparatus known as a cloud chamber. The radiation continued even after the source was removed. They created the first artificial radioactivity -
Italy's Erwin Schrödinger
He found the Quantum Mechanical Theory which is a significant probability of finding an electron in an atom at any position within a spherical volume surrounding the nucleus and it can have discrete energy levels. He also suggested that the movement of electrons are like waves. His theory was more liked than Heisenberg's, because it could be seen more visually. -
America's Linus Pauling
During his investigation of molecular structures, Pauling came up with a rule that dealt with the atomic arrangements in crystals with ionic bonding. He came up with this rule by using new techniques and mathematics. This helps scientists accurately predict and determine crystal structures. -
England's Chadwick
James Chadwick discovered neutrons during an investigation of beryllium. The goal of the investigation was the atomic disintegration which was only achieved with the discovery. He had found out that neutrons were the only particle able to pass electrical barriers because of its neutrality. -
England's Irene Joliot-Curie
Shs found the actions of neutrons in heavy elements, was a helpful step in the discovery of uranium fission -
Austria's Lise Meitner
After Otto Hahn took all the credit for the discovery of nuclear fission, Meitner wrote a paper explaining the observations of the experiment. -
England's Rosalind Franklin
She found the basic dimensions of DNA strands, and that the phosphates were on the outside of what was probably a helical structure, using X-ray crystallography.
