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500 BCE
Aristotle
Aristotle disagreed with Democritus' theory. .His ideas were not contradicted and agreed with by anyone until the 17th century. He greatly slowed down the evolution of the atomic theory by saying it didn't exist. -
400 BCE
Democritus
According to Democritus’ atomic theory, the universe and all matter obey the following principles:
Everything is composed of “atoms”, which are physically, but not geometrically, indivisible
Between atoms, there lies empty space
Atoms are indestructible
Atoms have always been, and always will be, in motion
There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. -
400
Leucippus
Proposed the same thing with Democritus -
1530
Paracelsus
He picked up the principle that metals were the key elements which made up the universe. Paracelsus argued that the body was a chemical system which had to be balanced not only internally, but which also had to be in harmony with its environment. On the basis of this idea, Paracelsus introduced new chemical substances into medicine, for instance the use of the metal mercury for the treatment of syphilis. -
1556
George Bauer (Georgious Agricola)
laid foundations of modern chemistry; developed systematic metallurgy and medicinal application of minerals. -
Alchemy
Alchemy is the art of understanding, deconstructing, and reconstruction of matter. It is composed of the 4 basic elements, Fire, Wind, Water, and Earth. Through the study of alchemy, Alchemists have succeeded in obtaining real world elements. -
Robert Boyle
It is Boyle's Law for which he remains most famous. This states that if the volume of a gas is decreased, the pressure increases proportionally. Understanding that his results could be explained if all gases were made of tiny particles, Boyle tried to construct a universal 'corpuscular theory' of chemistry. -
Antoine Lavoisier
Found that mass is conserved in a chemical reaction, but the number of hydrogen and oxygen atoms before and after the reaction is the same. -
Joseph Proust
He first published his Law of Definite Proportions. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created -
Jons Jakob Berzelius
He compiled a table of relative atomic weights, where oxygen was set to 100, and which included all of the elements known at the time. This work provided evidence in favor of the atomic theory proposed by John Dalton: that inorganic chemical compounds are composed of atoms combined in whole number amounts. -
Joseph Gay-Lussac
He proposed two fundamental laws of gases in the early 19th century. he concluded that equal volumes of all gases expand equally with the same increase in temperature: this conclusion is usually called “Charles's law." from his own and others' experiments he deduced that gases at constant temperature and pressure combine in simple numerical proportions by volume, and the resulting product or products—if gases—also bear a simple proportion by volume to the volumes of the reactants. -
Amadeo Avogadro
He is best known for his hypothesis that equal volumes of different gases contain an equal number of molecules, provided they are at the same temperature and pressure. His hypothesis was rejected by other scientists. It only gained acceptance after his death. It is now called Avogadro's law. He also clarified the distinction between atoms and molecules. Oxygen, Hydrogen, and nitrogen through elements, form diatomic molecules. -
J.J. Thomson
Discovered the electron, proved his theory using the cathode ray tube. The lights glowing inside the tube were in a straight line, and he could not explain why they did this. Soon after, he realized the glowing lights were smaller particles-smaller then the atom. He called those particles electrons. -
Atomic Models over time
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Atomic Models through time
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John Dalton
His theory stated that elements consisted of tiny particles called atoms. He combined oxygen and carbon and made two compounds, thus leading him to explain why elements would combine with one another in fixed ratios as combinations of these ratios -
Henri Becquerel
He was studying the fluorescent properties of uranium salts and placed a piece of the uranium salt on top of a photographic plate wrapped in black paper. He discovered, upon development, that the plate was exposed in the shape of the uranium sample. This discovered radioactivity.The radiation emitted by the uranium shared certain properties with x-rays and light. He and two students of his , Marie and Pierre Curie, shared the 1903 Nobel Prize in Physics for their studies in spontaneous radiation -
Max Planck
Revolutionized the field of physics by discovering that energy does not flow evenly but is instead released in discrete packets. Called this the Quantum Theory, which won him a Nobel Prize in 1918. -
Robert Millikan
He used Thomsons electron results, conducted his own experiment, called the oil drop method. He confirmed Thomsons theory. -
Niels Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Ernest Rutherford
He described the atom as having a central positive nucleus surrounded by negative orbiting electrons. His conclusion was gathered from using the gold and foil experiment, which included the firing and radioactive particles through thin metal foils and seeing them by using screens coated with zinc sulfide.He found out that most of the particles passed through the foil, 1 in 8000 bounced off, which lead him to believe that most of an atom is made up of empty space. -
Arthur Compton
Discovered the Compton effect which demonstrated the particle of nature of electromagnetic radiation -
Louis de Broglie
French physicist best known for his research on quantum theory and for predicting the wave nature of electrons. He gained worldwide acclaim for his groundbreaking work on quantum theory. In his 1924 thesis, he discovered the wave nature of electrons and suggested that all matter have wave properties. In 1929 he was awarded the Nobel Prize for Physics. -
Werner Heisenberg
Best known for his uncertainty principle and theory of quantum mechanics, which he published at the age of twenty-three in 1925. He was awarded the Nobel Prize for Physics in 1932 for his subsequent research and application of this principle. -
Erwin Schrodinger
He took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. -
Murray Gell-Mann
He introduced the concept of a quantum property and the force that holds the components of the atomic nucleus. He suggested a scheme for the classification of previously discovered strongly interacting particles into a basic and proper arrangement of families. He hypothesized it should be achievable to elaborate on the specific properties of known particles in terms of even more fundamental particles. He termed these particles of matter as “quarks”, later led to the discovery of omega-minus. -
Peter Higgs
He began in the Quantum field theory. He wrote what describes what later became known as the Higgs mechanism, in which a scalar field (that is, a field present at all points in space) gives particles mass.In the late 1960s American physicist Steven Weinberg and Pakistani physicist Abdus Salam independently incorporated Higgs’s ideas into what later became known as electroweak theory to describe the origin of particle masses. -
Carlo Rubbia
Rubbia provided one of the experimental clues that led to the formulation of the electroweak theory by observing neutral weak currents. These interactions differ from those previously observed and are direct analogues of electromagnetic interactions. The electroweak theory embodied the idea that the weak force can be transmitted by any of three particles called intermediate vector bosons. it indicated that these particles (W+, W-, and Z0) should have masses nearly 100 times that of the proton.
