History of atoms

• John Dalton


  Thought atoms were tiny spheres that could not be divided. 1804
• JJ Thomson


  discovered the electron, plum pudding model. 1898
• Ernest Rutherford

  Discovered the nucleus, gold foil experiment, nuclear model. 1909
• Neils Bohr

  Said that electrons are in energy levels, the further an electron was from the nucleus, the higher its energy -developed the planetary model. 1912
• James Chadwick 


  Discovered the neutron. 1934
• Alpha scattering experiment

  Alpha particles are fired at a thin gold foil.

  Alpha particles are He nuclei and consists of 2 protons and 2 neutrons. They are positively charged and fired at high speed.
• Order of discovery of subatomic particles

  electron-1897

  proton-1922

  neutron-1934
• subatomic particles

  
• Why is the atom neutral has no overall charge?

  Atom contains same number of protons(+) and electrons(-), which cancel eachother out hence it has no overall charge.