History of the atom

• John dalton

  • Tiny solid spheres
  • different spheres made different elements
• J.J thompson

  • Pum pudding model
  • contained negatively charged electrons
  • Positively charged atom with negatively charged electrons dotted on it
• Rutherford + Geiger and Marsden

  • fired positively charged alpha particles at a thin sheet of gold foil
  • Some alpha particles went straight through
  • Some reflected
  • Theory of nuclear atoms
  • Tiny positively charged nucleus
  • Most of the atom was empty space
• Bohr

  • discovery of electron shells
  • Each shell had a fixed energy
  • Electrons existed in fixed orbits or shells
• Mendeleev's Periodic table arrangement

  • rows of increasing atomic mass
  • Elements with lower atomic mass on the left
  • All the elements in column had similar properties
• Size of an atom

  1 x 10$^-10$m