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460
Democritus 460BC (Greece)
Democritus formulated the atomic theory for the universe; proposed that all matter is made of infinite indivisible particles which differ from each other in form, position & arrangement -
Isaac Newton (England)
Isaac Newton proposed the laws of gravitation and proposed a mechanical universe with small solid masses in motion. He also suggested that atoms were held together by attractions, now called forces. -
John Dalton (England)
John Dalton first suggested the existance of an atom. His original theories provided us with the weight of atoms which can distinguish one atom from another. Dalton also showed that there are 3 types of atoms existed: simple, compound & complex. -
George Johnstone Stoney (Ireland)
George Johnstone Stoney proposed the concept of the electron, that electricity was made of discrete negative particles called electrons, and calculated the electric charge of an atom. -
Joseph John Thomson (England)
Joseph John Thompson showed us the existance of subatomic particles through cathrode rays. The research on rays led to a means of separating atoms & molecules according to their atomic weights. Joseph discovered the electron and the isotype and also introduced the Plum Pudding model.
He postulated that the negatively charged electrons, he had discovered, were scattered throughout a cloud of positive charge, like the plums in plum pudding. -
Max Planck (Germany)
Max Planck was the founder of the Quantum theory. The Quantum theory has revolutionised our understanding of atomic and sub-atomic processes. Planck also created Planck’s Law of Black-body Radiation ( the intensity spectrum of electromagnetic radiation from a black body at temperature). -
Hantora Nagaoka (Japan)
Hantora Nagaoka created a ‘Saturnian‘ model of an atom with flat rings of electrons revolving around a positively charged atom based on the solar system analogy which helped us understand the structure of the atom. The model was the first to postulate a dense atomic central core. -
Robert Andrews Millikan (America)
Robert Andrews Millikan measured the charge of an electron using the oil drop experiment which allowed us to measure the charge to mass ratio of an electron. -
Ernest Rutherford (New Zealand)
Ernest Rutherford established that the nucleus was very dense, small and positively charged and assumed that the electrons were located outside the nucleus. The Rutherford model, or planetary, model of the atom, was pioneered.He is widely credited with first splitting the atom. -
Henry Gwyn-Jeffreys Moseley (England)
Henry Gwyn-Jeffreys Moseley arranged the periodic table by their atomic numbers and used X-ray tubes to determine the charges in the nuclei of most atoms. He experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and established the relationship between atomic number and the charge of the atomic nucleus. -
Neils Bohr (Denmark)
Niels Bohr developed an explanation of atomic structure that underlies regularities of the periodic table of elements. He also published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain consecutively larger orbits. -
James Chadwick (England)
James Chadwick used the alpha particles to discover a neutral atom particle with a mass close to a proton – thus discovered the neutron.. His discovery formed the base for the investigation of the tougher questions of nuclear physics: the nature of the nucleus and its forces.
