Atomic Structure

• Dalton agreed with Democritus that matter was made up of atoms and that atoms were indivisible
• JJ Thompson discovered the electron in 1897 and created the plum pudding model
• Rutherford fired alpha particles at gold foil called the alpha scattering experiment
• Rutherford discovered the nucleus of the atom when the alpha particles scattered
• Rutherford also proved that the nucleus was positive and most of the atom was empty space
• Neils Bohr said that electrons orbited the nucleus in shells or energy levels
• Chadwick proved the existence of the neutron
• If electrons absorb EM radiation, they can move between energy levels
• If electrons give out EM radiation, they move down an energy level
• Isotopes have the same number of protons but a different number of neutrons
• Unstable isotopes tend to decay to become more stable
• Alpha particles are a helium nucleus with 2 protons and 2 neutrons
• Alpha particles can be stopped by paper and are highly ionising
• Beta particles are high speed electrons that are emitted from the nucleus of an atom
• Beta can be stopped by aluminium and are moderately ionising
• Beta particles are used in medical tracers'
• Alpha particles are used in smoke detectors
• Gamma rays are EM waves with a short wavelength
• Gamma is stopped by concrete or lead and are weakly ionising
• Gamma rays are used in medical imaging and in the treatment of cancer.
• Gamma does not change the mass of a nucleus
• Radioactivity is random
• A half-life is the time it takes for a radioactive substance to half
• Background radiation is the radiation that is naturally present in the environment.
• Exposure to radiation is called irradiation
• Contamination is where the object is in direct contact with something
• The seriousness of Irradiation and contamination depends on the source
• Alpha and Beta sources cannot be detected from within the body so are dangerous if swallowed
• Radiation dose is measured in sieverts (Sv)
• Radioactivity is measured in Becquerels (Bq)
• Radiation can ionise cells and cause tissue damage
• Gamma sources can be used in medical tracers so that the tracer causes no harm to the person
• Radiotherapy uses radiation to kill cancer cells
• Nuclear Fission is splitting up of a large unstable nucleus into two smaller nuclei usually in plutonium and uranium
• Spontaneous fission is rare and usually the nucleus has to absorb a neutron before it will split
• Two or three neutrons are released when an atom splits
• Uncontrolled fission results in an explosion which sets of nuclear bombs
• Nuclear Fusion is where two light nuclei collide and fuse together to form a heavier nucleus
• Some of the mass of the lighter nuclei are converted to energy and released
• Fusion releases lots of energy but the temperature and pressure needed makes fusion reactors expensive and difficult to build