Scientific models of the atom

• Isotope


  A form of an element that has the same number of protons but a different number of neutrons
• Electron configuration


  Work out the electron configuration of the first 20 elements
• Scientific Models of the Atom


  • Early models: atoms were thought to be tiny spheres that could not be divided into simpler particles
  • Thomson model: atoms contained tiny, negative electrons surrounded by a sea of positive charge ('plum-pudding' model)
  • Rutherford model: positive charge in an atom must be concentrated in a very small area (the 'nucleus')
  • Bohr model: electrons must orbit the nucleus at specific distances, otherwise they would spiral inwards
  • Chadwick model: evidence of neutrons within the nucleus
• In 1898, Thomson discovered electrons and the representation of the atom had to be changed
• Overall, an atom is neutral, i.e. it has no charge
• Geiger and Marsden carried out an experiment in which they bombarded a thin sheet of gold with alpha particles, and a tiny number were deflected back towards the source
• Rutherford looked at these results and concluded that the positive charge in an atom must be concentrated in a very small area
• About 20 years after the nucleus became an accepted scientific idea, James Chadwick provided evidence of neutrons within the nucleus
• Later experiments led to the idea that the positive charge of a nucleus could be subdivided into a whole number of smaller particles, each with the same amount of positive charge. These particles are protons
• Atoms are very, very small and typically have an atomic radius about 0.1nm or 1 x 10-10m