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History of atomic theory. The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons. Atomic theory is the scientific theory that matter is composed of particles called atoms. The definition of the word "atom" has changed over the years in response to scientific discoveries.
Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. [1] Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed. A transmutation can be achieved either by nuclear reactions (in which an outside particle reacts with a nucleus ...
A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 Da), but this number will not be exactly an integer except (by definition) in the case of carbon-12. [65] The heaviest stable atom is lead-208, [57] with a mass of 207.976 6521 Da. [66]
Atomic electron transition. Change of an electron between energy levels within an atom. An electron in a Bohr model atom, moving from quantum level n = 3 to n = 2 and releasing a photon. The energy of an electron is determined by its orbit around the atom. The n = 0 orbit, commonly referred to as the ground state, has the lowest energy of all ...
3D animation of an atom incorporating the Rutherford model. The atomic nucleus shown expanded more than 10,000 times its size relative to the atom; electrons have no measurable diameter. The Rutherford model was devised by Ernest Rutherford to describe an atom. Rutherford directed the Geiger–Marsden experiment in 1909, which suggested, upon ...
Nuclear fission was discovered in December 1938 by chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch. Fission is a nuclear reaction or radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei and often other particles. The fission process often produces ...
An image from John Dalton's A New System of Chemical Philosophy, the first modern explanation of atomic theory.. This timeline of chemistry lists important works, discoveries, ideas, inventions, and experiments that significantly changed humanity's understanding of the modern science known as chemistry, defined as the scientific study of the composition of matter and of its interactions.
Rutherford scattering or Coulomb scattering is the elastic scattering of charged particles by the Coulomb interaction. The paper also initiated the development of the planetary Rutherford model of the atom and eventually the Bohr model. Rutherford scattering is now exploited by the materials science community in an analytical technique called ...