Atoms

Atoms

Atomic Structure
1. Rutherford scattering and the demise of the plum pudding
  1. In 1909 Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil. They expected that the positively charged alpha particles would be slightly deflected by the electrons in the plum pudding model.
    1. However most of the alpha particles just went straight through but the odd one came straight back at them. They realised this meant most of the mass that most of the mass of the atom was concentrated at the center in a tiny nucleus. They also realised the nucleus must have a large positive charge since it repelled the positive alpha particles by large angles. It also showed that most of an atom is just empty space
2. Rutherford and Marsden came up with the nuclear model of an atom
  1. The nucleus is tiny but makes up most of the mass of the atom. It contains protons (which are positively charged) and neutrons (which are neutral) which gives an overall positive charge. The rest of the atom is just empty space. The negative electrons move round the outside of the nucleus really fast. They give the atom its overall size
  2. Proton mass: 1
  3. Neutron mass: 1
  4. Electron mass: 1/2000
3. Number of protons equals number of electrons
  1. Atoms have no overall charge
  2. The charge on an electron is the same size as the charge on a proton but opposite
    1. This means the number of protons always equals the number of electrons in a neutral atom
  3. If some electrons are added or removed the atom becomes a charged particle called an ion
Atoms and radiation
1. Isotopes are different forms of the same element
  1. Isotopes are atoms with the same number of protons but a different number of neutrons
    1. They have the same atomic numbers but different mass numbers
  2. Atomic number is the number of protons + number of neutrons in an atom
  3. Most elements have different isotopes but theres usually only one or two stable ones
    1. The other isotopes tend to be radioactive which means they decay into other elements and give out radiation
2. Radioactivity is a Totally random process
  1. Radioactive substances give out radiation from the nuclei of their atoms. This process is entirely random. This means that if you have 1000 unstable nuclei you cant say when any one of them is going to decay and neither can you do anything at all to make a decay happen
  2. Radioactive substances spit out one or more of the three types of radiation
    1. alpha
    2. beta
    3. gamma
3. Background radiation comes from many sources
  1. This is radiation that is present at all times
  2. It comes from:
    1. Radioactivity of naturally occurring unstable isotopes which are all around us in the air, food, rocks etc
    2. Radiation comes from space which is known as cosmic rays. These are mostly from the sun
    3. Radiation due to man-made sources e.g. fallout from nuclear weapons tests etc
4. Radiation dose depends on location and occupation
  1. Radiation dose depends on the type and amount of radiation youve been exposed to. The higher the radiation dose the more at risk you are of developing cancer
  2. The amount of radiation youre exposed to can be affected by your location and occupation
    1. Certain underground rocks (e.g. granite) can cause higher levels at the surface especially if they release radioactive radon gas which tends to get trapped inside peoples houses
    2. At high altitudes (e.g. jet planes) the background radiation increases because of more exposure to cosmic rays
    3. Underground (e.g. mines) it increases because of the rocks all around
    4. Nuclear industry workers and uranium miners are typically exposed to 10 times the normal amount of radiation. They wear protective clothing and face masks to stop them touching or inhaling the radioactive material and monitor their radiation doses with special radiation badges and regular check ups
    5. Radiographers work in hospitals using ionising radiation and so have a higher risk of radiation exposure. They wear lead aprons and stand behind lead screens to protect them from prolonged exposure

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	Created by sian.allison almost 12 years ago