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400
Democritus
Democritus was an influential Ancient Greek pre-Socratic philosopher. Democritus made many very important discoveries in the span of his lifetime but the greatest was that of the atom. Democritus called his discovery "Atom" because he believed that the atom was unbreakable into smaller parts. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
400
Aristole
Aristotle was a Greek philosopher . He did not believe in the atomic theory . He thought that all materials on Earth were not made of atoms, but of the four elements : Earth,Water , Fire and Air. Aristotle started his own school called the Lyceum. His school had a broad range of subject, but showed emphasis on the study of nature. He believed that the element earth would be the center of the universe. He, even,developed the scientific method. -
John Daltn
John Dalton was a English chemist, physicist, and meteorologist. His atomic theory said that elements consisted of tiny particles called atoms. It states an element is pure because all atoms of an element are identical. All the atoms that make up the element have the same mass. All elements are different from each other due to differing masses. A compound is a pure substance due to different elements bonded together.Each atom has its own characteristic. Everything is made of atoms. -
J.J Thomson
J.J. Thomson discovered the electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges.The Cathode Ray Tube Experiment was also conducted by him and this experiment had majorly helped to discover the electrons ,too. -
Robert Millikan
Robert Millikan was an experimental physicist. J J Thompson came up with the charge to mass ratio of an electron already, but did not discover the actual charge or mass of one electron. Using and oil-drop experiment he found the charge of one single electron. He made it possible to measure the charge of an electron. -
Ernest Rutherford
Ernest Ruthford was a British physicist who became known as the father of nuclear physics. He proposed that the nucleus was dense and positively charged and Rutherford's Gold Foil Experiment showed exactly that. He also proved that most of the atom was made of empty space. Moreover, he assumed that the electrons were located outside the nucleus. -
Neils Bohr
Neils Bohr was a danish physicist. He proposed an atomic theory that stated an orbit of an atom could hold more electrons than the inner orbit.The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr 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.The element Bohrium , No. 107 on the Periodic Table is named after him. -
Sir James Chadwick
Sir James Chadwick was a english phsicist.He proved the existence of neutrons in 1932. He discovered the fourth subatomic particle,the neutron. He established that atomic number is determined by the numbers of protons in an atom. As uncharged particles in atoms, neutrons play a key role in the splitting of atoms - Chadwick prepared the way towards the fission of uranium-235 and towards the creation of the atomic bomb.
