models of atoms

• In the 1800's John Dalton described atoms as solid spheres, and suggested that different types of spheres make up the different elements.
• plum pudding model - atom consists of a ball of positive charge with negative electrons embedded
• In Rutherford's experiments, alpha particles were fired at a thin sheet of gold foil.

  Most particles passed through, but some were deflected off course. 

  This caused him to hypothesise that there was a dense region of positive 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 negative electrons. 
• neils bohr discovered the electrons orbit the nucleus in shells
• james chadwick discovered the neutrons