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420 BCE
Democritus (Ancient Atomic Theory)
One of the first atomic theorists was Democritus, a Greek philosopher who lived in the fifth century BC. Democritus knew that if a stone was divided in half, the two halves would have essentially the same properties as the whole.Therefore, he reasoned that if the stone were to be continually cut into smaller and smaller pieces then; at some point, there would be a piece which would be so small as to be indivisible. He called these small pieces of matter "atomos," the Greek word for indivisible. -
John Dalton (Billard Ball Model)
John Dalton's atomic theory was generally accepted because it explained the laws of conservation of mass, definite proportions, multiple proportions, and other observations. Dalton proposes that the indivisible unit of life is the atom. Dalton's failure consists in that he didn't represent the different electronic charges in the atom and he represented it as a completely full sphere -
Billard Ball Model
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J. J. Thomson (Plum Pudding Model)
In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio. His failure was that he didn't represent well the elecric charges distribution and the orbital movements of the atom elements. -
Plum Pudding Model
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Ernest Rutherford (Nuclear Model)
Rutherford's model shows that an atom is mostly empty space, with electrons orbiting a fixed, positively charged nucleus in set, predictable paths. His representation was almost correct, in fact, it is used as the common representation of the atom, but the energical distribution isn't very exact though. -
Nuclear Model
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Rutherford's Experiment
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. -
Niels Bohr (Planetary Model)
In atomic physics, the Rutherford–Bohr model or Bohr model or Bohr diagram, presented by Niels Bohr and Ernest Rutherford in 1913, is a system consisting of a small, dense nucleus surrounded by revolving electrons similar to the structure of the Solar System, but with attraction provided by electrostatic forces. He didn´t represent the proportions of every charge. -
Planetary Model
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Erwin Schrodinger (Quantum Model)
In 1926 Erwin Schrödinger, an Austrian physicist, 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. This is the most accepted model by actual scientists. -
Quantum Model
