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Democritus
The famous Greek thinker Democritus proposed a few points to his theory of atoms.
All matter is composed of atoms, which are bits of matter too small to be seen.
These atoms cannot be further split into smaller portions.
There is a void, which is empty space between atoms.
Atoms are completely solid and
are different in: their sizes, their shapes, and their weights. -
Isaac Newton
English Physicist Sir Isaac Newton theorized that the universe was made up of small, solid masses in motion and stated of some definite size which combine in many ways to produce substance. -
John Dalton Model
in the early 1800s John Dalton stated that elements consisted of tiny particles called atoms. He said that all atoms of an element were identical and that they had the same mass. He also said that compounds consisted of atoms of different elements combined together. -
James Clerk Maxwell
James Clerk Maxwell's principal contribution to the atomic concept had to do with his theory of electromagnetism. Maxwell's laws predict that any system in which a charged particle orbits about an oppositely charged particle (for example, an electron orbiting about the nucleus) should emit light at a frequency related to the radius of the orbiting particle. -
Dmitri Mendeleev
Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869. -
G.J Stoney
A famous Anglo-Irish physicist theorized that electricity was comprised of negative particles he called electrons. Stoney's most important scientific work was the conception and calculation of the magnitude of the atom or particle of electricity, for which he created the term "electron". -
J.J Thompson Model
The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model. In this model, the atom is composed of electrons surrounded by a pool of positive charge to balance the electrons' negative charges. -
Alpha particles
Discovered and named by Ernest Rutherford, alpha particles are positively charged particles emitted by some radioactive substances, consisting of two protons and two neutrons bound together, thus having a mass of four units and a positive charge of two. alpha particles were used by Rutherford and coworkers in experiments to probe the structure of atoms in thin metallic foils. -
Gold Foil Experiment
The diagram shows a simplified plan of his gold foil experiment. A radioactive source capable of emitting alpha particles was enclosed within a protective lead shield. The radiation was focused into a narrow beam after passing through a slit in a lead screen. A thin section of gold foil was placed in front of the slit, and a screen coated with zinc sulfide to render it fluorescent served as a counter to detect alpha particles. Rutherford found that although the vast majority of particles passed -
Ernest Rutherford Model
Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons.This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. -
Niels Bohr Model
Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit. He applied quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. -
James Chadwick
Chadwick proofs the existence of the neutron in 1932 what accelerated the research in nuclear physics inmensely. He was able to determine that the neutron did exist and that its mass was about 0.1 percent more than the proton's. He published his findings with characteristic modesty in a first paper entitled "Possible Existence of Neutron." In 1935 he received the Nobel Prize for his discovery.
