particle model

• 1800 - John Dalton


  he said everything was made out of solid spheres called atoms, which could not be divided.
• 1897 - JJ Thomson


  discovered that atoms must contain something smaller and negatively charged - electrons. he made the plum pudding model --> a sphere of positive charge with electrons embedded inside
• 1909 - gold foil experiment


  ernest rutherford working with ernest marsden and hans geiger, they conducted the gold foil experiment.

  the launched positively charged alpha particles at an extremely thin sheet of gold. most particles went straight through, some were slightly deflected but a few were deflected back.
• nuclear atom - rutherford


  a small, positive nucleus in the centre, with a cloud of electrons around it. but most of the atom was empty space
• neils bohr 


  nuclear model --> the electrons are in shells, orbiting the nucleus
• radius of the atomic nucleus is 1 x 10 -15 m. the diameter of an atom is about 1 x 10 -10 m
• sub atomic structures

  A) proton

  B) 1

  C) 0

  D) -1

  E) electron

  
• electrons lie at different distances from the nucleus, in different energy shells. this can vary based on the interactions with EM radiation.
• density = mass / volume
• p = m / v
• density depends on the spacing of atoms, how much volume they take up.
• solids and liquids have similar and higher densities, as the space between particles doesn't change that much.
• the average density of an object determines whether it floats or sinks. a solid object with float on a fluid if the average density [of the object] is less than that of the fluid.
• gases have much lower densities as the space between particles is greater. gas particles have lots of kinetic energy to move, so they occupy a greater volume, decreasing their density compared to solids and liquids.
• PAG - finding the density


  1. fill the eureka can so the level is just below the spout.
  2. place a measuring cylinder under the spout and gently lower the object in using a thin, strong thread. [the displaced water will come out of the spout].
  3. wait for the spout to stop dripping and measure the volume of water collected in the cylinder. --> volume of water displaced by the object = volume of the object
  4. repeat 3 times and calculate a mean.
• PAG - finding the density

  A) eureka

  B) displaced

  C) cylinder

  D) object