Development of the Model of the Atom

• Democritus - 500 BC

  Atomic theory is the idea that all matter is made up of tiny particles that can't be broken down any further.
• John Dalton - 1800's

  Described atoms as solid spheres and different types of spheres made up different elements.
• J.J Thompson - 1897

  Came up with the plum pudding model which proved that atoms could not be solid sphere and instead must've contained negatively charged particles (electrons)

  With this new theory the atoms was now seen as a general ball of positive charge with discrete electrons stuck in it.
• Ernest Rutherford - 1909

  took part in an experiment which fired alpha particles into a thin sheet of gold foil, however some particles where deflected to the side or even on small occasion back the way they had come.

  He then proposed the nuclear model of the atom which was a compact nucleus which contained all of the positive charge and the negative charge existed in a sort of cloud around the central nucleus, however if that were true nothing would stop the negative charge from rushing into the positive nucleus which would make the atom automatically collapse.
• Niels Bohr - 1913

  suggested that the electrons orbited the nucleus which were held in shells (orbiting of electrons is what prevents the atom from collapsing)
• Further experiments by Ernest Rutherford - 1917

  found that the positive charge of the nucleus is made up of small discreet particles known as protons
• James Chadwick - 1932

  provided evidence of neutral particles in the nucleus known as neutrons.
• Democritus 500 BC - Atomic Theory

  John Dalton 1800's - Solid Spheres

  J.J Thompson 1897 - Plum Pudding Model

  Ernest Rutherford 1909 - Nucleur Model

  Niels Bohr 1913 - Electron Shells

  Ernest Rutherford 1917 - Protons

  James Chadwick 1932 - Neutrons
• In Rutherford's experiments,  particles were fired at a thin sheet of gold foil. Most particles passed through, but some were  off course. 

  This caused him to hypothesise that there was a dense region of  charge at the centre of the atom that repelled the alpha particles.

  As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surround by  electrons. 
• One issue with Rutherford's nuclear model was that the atom should collapse as the negative electrons would be attracted to the positive nucleus, causing them to rush inwards.