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400
Democritus- 400 B.C.
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.
->Solids are made of small, pointy atoms.
->Liquids are made of large, round atoms.
->Oils are made of very fine, small atoms that can easily slip past each other. -
Period: 400 to
History of the Atom
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Antoine Lavoiser
The first breakthrough in the study of chemical reactions resulted from the work of the French chemist Antoine Lavoisier between 1772 and 1794. Lavoisier found that mass is conserved in a chemical reaction. The total mass of the products of a chemical reaction is always the same as the total mass of the starting materials consumed in the reaction. His results led to one of the fundamental laws of chemical behavior: the law of conservation of matter, which states that matter is conserved in conve -
Dmitri Mendeleev
Wrote 65 know elements and their atomic weight. And made the Periodic table based on their behavior. -
John Dalton
He was seriously interested in meteorology for the longest time. His interest in meteorology led him to his view of atomism. Once he got into atomism, he calculated atomic weights and came up with his Atomic Theory. John’s atomic theory said that elements consisted of tiny particles called atoms. It states an element is one of a kind (aka pure) because all atoms of an element are identical. All the atoms that make up the element have the same mass. Elements are different from other due to matter -
Eugen Goldstein
He noted that cathode-ray tubes with a perforated cathode emit a glow from the end of the tube near the cathode. Goldstein concluded that in addition to the electrons, or cathode rays, that travel from the negatively charged cathode toward the positively charged anode, there is another ray that travels in channels, in the cathode, Goldstein called them canal rays. -
J.J. Thomson
Discovered electrons and shown that they can be divided. Also that atoms are made of positively charged core and negatively charged particles. He developed the Plum Pudding Model before the atomic nucleus was discovered. -
Period: to
History of the Atom
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Max Planck
Planck made many contributions to theoretical physics, but his fame rests primarily on his role as originator of the quantum theory. This theory revolutionized our understanding of atomic and subatomic processes, just as Albert Einstein’s theory of relativity revolutionized our understanding of space and time. -
Ernest Rutherford
He discovered alpha and beta rays, Set the law for radioactive decay Most important, he suggested the nuclear structure of the atom: experiments done in his lab showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass. -
Niels Bohr
He passed on the study of the structure of atoms on the basis of Rutherford’s discovery of the atomic nucleus. By introducing conceptions borrowed from the Quantum theory as established by planck, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements, still fitly serves as an elucidation of the physical and chemical properties of the elements. -
Henry Moseley
He published the results of his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number. -
Robert Millikan
He discovered that electrons are 1000 times lighter than the smallest atom. In his experiments, A source of x-rays was then used to ionize the air in the chamber by removing electrons from the molecules in the air. Droplets that did not capture one of these electrons fell to the bottom of the chamber due to the force of gravity. Droplets that captured one or more electrons were attracted to the positive plate at the top of the viewing chamber and either fell more slowly or rose toward the top. -
Werner Heisenberg
He was a german theoretical physicist who made foundational contributions to quantum theory. He is best known for the development of the matrix mechanics formulation of quantum mechanics and for asserting the uncertainty principle, although he also made important contributions to nuclear physics, quantum field theory and particle physics. -
Erwin Schrodinger
He began to think about explaining the movement of an electron in a n atom as a wave. He then published his work, providing a theoretical basis for the atomic model that Niels Bohr had proposed based on laboratory evidence. The equation at the heart of his publication became known as Schrodinger’s wave equation. -
James Chadwick
Sent alpha particles of helium nuclei against beryllium and in 1932 discovered that there were neutrally charged particles that weigh as much as a proton were emitted.
