Unit 4 - Atomic Structure

• John Dalton


  agreed that matter was made up of tiny spheres, called atoms, that couldn't be broken up but believed each element was made from different atoms.
• John Dalton year of discovery

  1804
• JJ Thomson


  Discovered particles called electrons, and that atoms where spheres of positive charge with tiny electrons stuck in it, like a plum in a pudding.
• J.J. Thomson year of discovery:

  1897 (nearly 100 years later to John Dalton)
• Rutherford


  1909, discovered the positively charged nucleus
• Alpha particle scattering experiment


  occurred in 1909, where in Rutherford's lab, alpha particles were shot at a thin gold foil of paper. Students expected the particles to pass right through and for some to be deflected by the electrons IF THE PP MODEL WAS TRUE, and many of them did, however some were deflected and a few came straight back. These results showed that there was a positively charged nuclei at the centre of the atom.
• Why is it said that the nucleus small in the atom?


  Because very few positively charged alpha particles were deflected straight back.
• Why are some alpha particles deflected at large angles?

  Due to the large positive charge of the nucleus
• The alpha particle scattering experiment led to the existence of


  the nuclear model
• Bohr concluded (1913)


  That electrons rotate around the nucleus in fixed distances (called energy levels)
• 1932 James Chadwick


  Discovered the neutron, providing the understanding of the imbalance between the atomic and mass number
• the number of protons always equals


  the number of neutrons

  
• atomic mass


  Number of protons and neutrons
• atomic number


  number of protons
• ionisation


  when an atom seems to have lost or gained electrons and so it seems to have become an ion, it has become ionised
• isotopes


  different forms of the same element which have the same number of protons but different number of neutrons.
• radioactive decay


  unstable ions decay into other elements and give out radiation as they tend to be more stable
• ionising radiation


  emitted by radioactive substances and is radiation that knocks electrons of atoms, creating POSITIVE IONS.
• Alpha particles


  dont penetrate far into materials and are stopped quickly, as they travel only a few cm in air and are absorbed by a sheet of apper. they are relatively big and heavy, and due to their size are extremely iosnising as they bash into other elements.
• alpha radiation is used in


  smoke detectors. the alpha particles ionise the air particles creating a current. if smoke is present it will bind onto the air and so less air will flow, closing down a current, detecting smoke.
• beta particles


  they move quite fast and are quite small, so they can move in air for about 5metres and absorbed by a sheet of aluminium. moderately ionising and travel moderately far before ionising other objects (knocking electrons off and so creating positive ions)
• gamma particles


  gamma rays are small and fast, which makes them weakly ionising as they quickly pass through air and materials without touching other atoms. they travel quite far until touching another material, where they will do damage. absorbed by thick lead or metres of concrete.
• when are beta particles used


  used to test the thickness of thin sheets of metal as they are not absorbed as quickly as alpha particles but not as penetrating as gamma rays.
• when are gamma particles used?


  when a source needs to be detected in a thick material, for example a crack in pipes.
• Activity


  radioactive substances will give off radiation from the nuceli forever. the amount of radiation given off can be measure using a Geiger-Müller rube, recording the count rate
• count rate


  amount of radiation emitted for it to halve
• half-life


  the time it takes for the number of radioactive nuclei in an isotope to halve
• a short half-life means


  a lot of radiation being emitted in a short period of time as the nuclei decays.
• activity in a short half-life


  falls quickly
• objects with a short half-life


  are dangerous as in the beginning they will emit a lot of radiation as the nuclei decays.
• long half-life means


  activity falls slower as the amount it takes for the nuclei to decay is slower, it doesn't decay fully for a long time
• objects with a long half-life


  are dangerous as they keep emitting radiation into the environment for a very long period of time
• activity in a long half-life


  falls slower
• irradiation


  when objects are exposed to radiation. it doesnt make an object radioactive, but irradiation to living things can be harmful
• contamination


  when unwanted radioactive atoms get onto or into a material
• contamination is especially dangerous because

  radioactive particles could get inside your body
• Outside of the body, which radiation is the most dangerous?

  beta and gamma. this is because they can penetrate into the skin and organs, whereas alpha particles cannot penetrate skin and are blocked by air gaos.
• Inside of the body, which radiation is the most dangerous?


  Alpha particles as when travelling through, it can bash with many atoms inside the body whereas beta and gamma are likely to pass through quickly and may not touch many atoms.
• why is it important that research is published on radioactive particles?


  so that we can protect ourselves against harmful particles to enter out body.
• radiation dose


  amount of ionising radiation a person receives