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Democritus
Democritus adopted the atomic theory. It stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” He thought that atoms were small amounts of matter. He believed atoms cannot be destroyed, be different in size and shape, and are always moving. -
Joseph Louis Proust
He published 'The Law of Constant Compisition' in 1794. This law states that compounds are composed of elements exact proportions by mass no matter how the compound was created. -
John Dalton
He was an English chemist and made Dalton's Atomic Theory, which consitsted of four things. It stated that all matter is made of atoms. Atoms are indivisible and indestructible, all atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, and a chemical reaction is a rearrangement of atoms. -
Antoine Lavoisier
He found out that mass was reserved in a chemical reaction and that the mass of the products of a chemical reaction is the same as the starting materials consumed in a reaction. His research led to the law of conservation of matter. -
Michael Faraday
Studied the effect of electricity on solutions, created "electrolysis" which is splitting of molecules with electricity. Also developed laws of electrolysis. -
Henri Becquerel
He discovered that a piece of mineral that contains uranium could produce its image on a photographic plate in the absence of light. It led to the discovery of radioactivity. -
J.J. Thomson
He created better equiment and methods using rays and a vacuum. He also determined that all matter is made of tiny particles and discovered that atoms are the smallest fundamental unit. He proved the existance of isotopes. -
Max Planck
Max Planck proposed the quantum of action, now known as Planck's constant h, which states the pattern of light intensity emitted from a black body at any given frequency. This means that energy is not continious and energy is equal to the frequency of radiation multiplied by the universal constant -
Mrie and Perre Crie
They discovered new spontaneously radiating elements known as Polonium and Radium. They began to isolate the elements to find there chemical properties. -
Robert Milikan
He measured the charge of an electron with an oil-drop apparatus. The mass of an electron is at least 1000 times smaller then the lightest atom. -
Lisa Meitner
Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction. -
Albert Einstein
He published the Special Theory of Relativity and he created evidence for the atomic hypothesis. -
Niels Bohr
Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. He was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -
Erwin Schrödinger
He used math equations to describe the probability of finding an electron in a certain position. The atomic model is also known as The Quantum Mechanical Model of the Atom. -
James Chadwick
Discovered that Joiliot's Beam was not delfected by either electric or magnetic fields. This means it contains neutral paritcles, a neutron. -
Louis DeBroglie
He discovered that similar to light, elctrons could act as both particles and waves. -
Plum Pudding Model
-J.J. Thompson
An atom made of thousands of electrons would have a very high, negative electric charge. This was not observed, as atoms are usually uncharged. Thomson suggested that atoms contained far fewer electrons, a number roughly equal to the atomic number. This is only one electron in the case of hydrogen, far fewer than the thousands originally suggested. These electrons must have been balanced by some sort of positive charge. The distribution of charge and mass in the atom was unknown. -
Ernest Rutherford
Created the Rutherford Atomic Model and it described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. -
The Planetary Model
-Niels Bohr
Atom illustrated in the adjacent figure that is used as a symbol for atomic energy. The neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. -
Electron Cloud Model
-John Dalton
Electrons swarm around the nucleus of an atom in unpredictable movements. Scientists can make guesses about where electrons are likely to be at any given time. -
Quantum Mechanical Model
-Erwin Schrödinger
Took the Bohr atom model one step further. 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. -
Otto Hahn
Famous for the discvering the fission of uranium. This discovery actually directly led to the development of the atomic bomb. Also used beta-rays to test radioactivity. -
Glen T. Seaborg
Most famous for discovering the elements, Plutonium and Califronium. Also discovered 9 transuranic elements and was against atomic and nucleur wars. -
Aristotle
He did not believe in the atomic theory; he taught against it saying that everything was made of the four elements, fire, water, air, and earth. They were proved incorrect.
