atoms

• neutron has the same mass a

  proton

  
• electron has a

  negative charge
• electron has a mass

  of nearly nothing

  
• proton has the mass as

  neutrons
• protons have what type of charge

  positive
• isotope are different forms of the same element with same number of protons ad electrons


  but different numbers of neutrons
• when an atom is neutral it has the

  same number of protons and electron
• Dalton believes that atoms where thought to be

  tiny spheres that could not be divided

  
• Thompsons model was

  the discovery of the electron

  
• the discovery of the electron led to the

  plum pudding model
• the plum pudding model suggested that the atom is a

  ball of positive charge with negative electrons embedded in it
• Ernest Rutherford's experiment led to 3 conclusions which include

  the mass of an atom was concentrated at the center.

  the nucleus was charged.

  the discovery of the nucleus.

  
• Ernest Rutherford did an experiment to test the

  plum pudding model.
• His two students directed a beam of alpha particles at a

  very thin gold leaf suspended in a vacuum.

  
• label the items

  in Rutherford's experiment

  A) alpha particle

  B) scintillation screen

  C) gold foil

  
• Neils Bohr adapted the nuclear model by

  suggesting that electrons orbit the nucleus at specific distances

  
• Ernest Rutherford's model

  The vacuum is important because any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections off anything else.

  
• in Ernest Rutherford's model ,gold was used because

  
  

  
  

  it was the only metal that could be rolled out to be very, very thin without cracking.
• in Ernest Rutherford's model it was thought that the

  alpha particles could pass straight through the thin foil, or possibly puncture it.

  
• If the plum pudding model had been correct then all of the fast, highly charged alpha particles

  would have whizzed straight through undeflected. 
• in Ernest Rutherford's model the following happened

  • most of the alpha particles did pass straight through the foil
  • a small number of alpha particles were deflected by large angles as they passed through the foil
  • a very small number of alpha particles came straight back off the foil

  
• he fact that most alpha particles went straight through the foil is evidence for

  the atom being mostly empty space

  
• A small number of alpha particles being deflected at large angles suggested that there is a

  -concentration of positive charge in the atom

  • like charges repel,
  • so the positive alpha particles were being repelled by positive charges

  
• • the very small number of alpha particles coming straight back suggested that the 'target' being aimed at had to be equally tiny

  Positive charge and mass are concentrated in a tiny volume in the atom (the nucleus)

  The tiny number doing this means the chance of being on that exact collision course was very small,

  And so the 'target' being aimed at had to be equally tiny.
• Rutherford had discovered the nuclear atom, a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.
• later experiments led to the idea of a what charge

  positive

  
• positive charge was given what name

  proton

  
• the experimental work of who led to discovery of neutrons within the nucleus

  James Chadwick

  
• what James Chadwick find

  neutrons

  
• in a plum pudding model electrons are embedded but the recent model shows

  electrons orbiting the nucleus
• in the plum pudding model the nucleus has a

  positive charge