P4-Atomic Structure

• Rutherford replaced the plum pudding model with the nuclear model
• Rutherford tried firing a beam of alpha particles at thin gold foil. from the plum pudding model they expected the particles to pass straight through the sheet , some were deflected more than expected and a few were deflected back the way they had come something the plum pudding model couldn`t explain. from this they realised the mass was concentrated at the centre in a tiny nucleus and must have a positive charge and also the atom must be mostly empty space
• nuclear model that resulted from the alpha particle scattering experiment was a positively charged nuclease surrounded by a cloud of negative electrons
• current model of atom

  A) tiny

  B) protons

  C) neutrons

  D) 10000

  E) empty space

  F) no overall charge

  G) higher

  H) closer

  
• alpha radiation is when an alpha particle is emitted from the nuclease an a-particle is two neutrons and two protons. they don`t penetrate very far into materials and are stopped quickly they can only travel a few cm in air and are absorbed by a sheet of paper
• beta particle is simply a fast moving electron released by the nuclease beta particles have virtually no mass and a charge -1. they are moderately ionising and they penetrate moderately far into materials before colliding and have a range in air of a few metres they are absorbed by a sheet of aluminium around 5mm
• gamma rays are waves of electromagnetic radiation released by the nuclease they penetrate far into materials without being stopped and will travel a long distance through the air this means they are weakly ionising because they tend to pass through rather than collide with atoms eventually hitting something and do damage. they can be absorbed by thick sheets of lead of metres of concrete
• mass and atomic number have to balance
• alpha decay decreases the charge and mass of the nucleas
• beta decay increases the charge of the nucleus
• gamma rays don`t change the charge or mass of nucleus
• half life. radio active decay is entirely random however you can find out the time taken for the amount of radiation emitted by a source to halve

  A) half life

  B) activity

  
• exposure to radiation is called irradiation
• ionising radiation can enter living cells and ionise atoms within them which can cause cancer
• contamination is radioactive particles getting onto objects and you can avoid this by wearing gloves or using tongs or using a protective suit
• beta and gamma are the most dangerous and once on the skin can get onto organs
• alpha is less penetrating and cant penetrate the skin