History of Development of the Model of Atom

Table below shows the scientists that contribute to the development of the Model of Atom.

John Dalton

  • Five main points of Dalton's Atomic Theory
  • All matter is composed of extremely small particles called atoms.
  • All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of a specific element are different from those of any other element.
  • Atoms cannot be created, divided into smaller particles, or destroyed.
  • Different atoms combine in simple whole-number ratios to form compounds.
  • In a chemical reaction, atoms are separated, combined, or rearranged.
Weakness
  • Atoms consist of even smaller particles called electrons, protons and neutrons.
  • Atoms can be created and destroyed in the nuclear reactions such as nuclear fusion and nuclear fission..
  • Atoms of the same element can have different physical properties, for example, isotopes of hydrogen.
J.J. Thomson The electrons were positioned uniformly throughout the atom.
Ernest Rutherford
  • the atom is mostly empty space,
  • most of the atom's mass concentrated in a tiny center, the nucleus and electrons being held in orbit around it by electrostatic attraction.
  • The nucleus was around 10-15 meters in diameter, in the centre of a 10-10 metre diameter atom.
  • Those alpha particles that had come into close proximity with the nucleus had been strongly deflected whereas the majority had passed at a relatively great distance to it.
Neils Bohr
  • Electrons in an atom of an element are not randomly distributed around the atomic nucleus.
  • Electrons move around the nucleus in fixed orbits.
  • Each orbit forms a circle and has a fixed distance from the nucleus.
James Chadwick
  • Chadwick discovered the presence of neutrons in the nucleus.
  • He concluded that the nucleus contains another tiny particle known as a neutron that has no charge.
  • The neutron mass is almost similar to the proton mass.
  • All nuclei contain protons and neutrons, except for the hydrogen which contains protons. only


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