atomic structure physics

• who came up with the idea that all matter was made up of identical lumps ?

  Democritus
• what century did Democritus come up with this idea?

  5th century
• Did John Dalton agree with Democritus?

  Yes he did - he believed all matter was made up up of tiny spheres called atoms that couldn't be broken apart
• what did John Dalton also believe?

  He reckoned that elements are made up of different type of atom
• what year did John Dalton discover this?

  1804
• What did JJ Thomson discover?

  He discovered electrons - that could be removed from the atom

  So, Johns theory wasn't quite right!
• What was model he discovered?

  Plum Pudding Model - He suggested that atoms were spheres of positive charge with negative electrons stuck in it
• why is it called the plum pudding model?

  the sphere of positive charge with negative electrons are like fruit in a plum pudding
• what happened in 1909?

  scientists in Rutherford's lab conducted the alpha scattering experiment
• what is the alpha scattering experiment?

  a beam of alpha particles were fired at a thin sheet of gold foil
• what did they expect to happen from the alpha scattering experiment?

  they expected all the particles to go straight through due to the Plum pudding Model, or only be slightly deflected.
• what actually happened?

  most of the particles did go straight through, but some were deflected more than expected, some were deflected back the way they had come - something the plum pudding model couldn't explain
• what were the conclusions based on the results from the alpha scattering experiment?

  most of the mass is concentrated in the centre of the atom in a tiny nucleus - because a few particles were deflected back

  then nucleus was positive charge - it repelled the positive alpha particles

  most of the atom is empty space - most of the particles went straight through
• what was the nuclear model that resulted from the alpha scattering experiment look like?

  a positive charged nucleus surrounded by a cloud of negative electrons
• What did Niel Bohr do find?

  he said electrons orbiting the nucleus do so at certain distances
• how was this proved?

  by his theoretical calculations
• what was the further evidence that changed the model?

  further experiments changed the model to have a nucleus made up of group of particles (protons) that all have the same positive charge that added up to the overall charge of the nucleus
• what did james chadwick do?

  20 yrs later he proved the existence of the neutron - this explained the imbalance between the atomic and mass numbers
• how can electrons in the energy levels move within the atom?

  if they gain energy by absorbing EM radiation - they move to a higher energy level , further from the nucleus

  if they release EM radiation they move close to the nucleus

  if one or more outer electrons leave the atom - the atom become a positive charged ion