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Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small “atoms.” Aristotle famously rejected atomism in On Generation and Corruption. -
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Dalton assigned atomic weights to the atoms of the 20 elements he knew of at the time. -
He defined an atom to be a ball-like structure, as the concepts of atomic nucleus and electrons were unknown at the time. If you asked Dalton to draw the diagram of an atom, he would've simply drawn a circle! -
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Faraday continued his electrical experiments. In 1832 he proved that the electricity induced from a magnet, voltaic electricity produced by a battery, and static electricity were all the same. -
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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 the opposite direction, from the anode toward the cathode. -
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The gold-foil experiment showed that the atom consists of a small, massive, positively charged nucleus with the negatively charged electrons being at a great distance from the centre. -
The atom, as described by Ernest Rutherford, has a tiny, massive core called the nucleus. The nucleus has a positive charge. Electrons are particles with a negative charge. Electrons orbit the nucleus. -
Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
The plum pudding model depicts the electrons as negatively-charged particles embedded in a sea of positive charge. -
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the revolution that ended the Portuguese Monarchy. It was caused by a coup d'état organized by the Portuguese Republican Party. End of the monarchy and start of the republic. King Manuel II flees to England. -
His oil drop experiment confirmed the existence of the electron and accurately determined its charge. -
Niels Bohr change the atomic theory by realizing that the electrons did not crash into the nucleus as would be expected in classical physics. Classical physics says that opposites attract and likes repel, so the negative electrons should be attracted to the positive nucleus. -
The perspective that the morphology of the atom is similar in many ways to the structure of the solar system was proposed by Niels Bohr in 1915 and has become known as the “planetary model” of the atom. The atom has a central body, the nucleus, around which the electrons orbit -
The Polish–Soviet War (14 February 1919 – 18 March 1921) was fought primarily between the Second Polish Republic and the Russian Soviet Federative Socialist Republic, following World War I and the Russian Revolution, over territories previously controlled by the Russian Empire and the Habsburg monarchy. -
Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly. -
The electron cloud model shows a particular area in which an electron is likely to be. In a simple atom like Helium for instance, the probability field is a sphere surrounding the nucleus, and the electron is more likely to be closer to the nucleus than far away from it. -
Erwin Schrödinger showed that the quantization of the hydrogen atom's energy levels that appeared in Niels Bohr's atomic model could be calculated from the Schrödinger equation, which describes how the wave function of a quantum mechanical system (in this case, a hydrogen atom's electron) evolves. -
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The electron cloud model best represents our current understanding of the atomic structure. The electron cloud model describes the atom as containing a dense nucleus of protons and neutrons surrounded by regions of space (clouds) where electrons are most likely to be found. -
James Chadwick's contribution to the atomic model was his discovery of the neutron. The neutron is a neutrally charged subatomic particle that is about the same mass as the proton. Both protons and neutrons occupy the nucleus of the atom. -
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