Atomic Structure

Atomic Structure

1. Isotopes are Different forms of the same element

   • All atoms of each element have a set number of protons (each nucleus has a given positive charge). The number of protons in an atom is its atomic number.
     • The mass number of an atom ( the mass of the nucleus) is number of protons + the number of neutrons in its nucleus.
       • Isotopes of an element are atoms with the same number of protons ( the same atomic number, and so the same charge on the nucleus) but a different number of neutrons ( a different mass number).
         • All elements have different isotopes, but there are usually only one or two stable ones.
           • The other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable (they try to balance the number of protons and neutrons in their nucleus or get rid of any excess energy). This process is called radioactive decay.
             • Radioactive give out one or more types of ionising radiation for their nucleus- these are alpha, beta and gamma radiation.
               • They can also release neutrons when they decay to rebalance the number of protons and neutrons.
                 • Ionising radiation is radiation that knocks electrons off atoms, creating positive ions.

2. Alpha Particle

   • Alpha radiation is where an alpha particle is emitted from the nucleus.
     • An alpha particle is two neutrons and two protons ( like a helium nucleus).
       • 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. Also because of their size they are strongly ioninsig.

3. Beta Particle

   • A beta particle is simply a fast-moving electron released by the nucleus . Beta particles have virtually no mass and a charge of -1.
     • They are moderately ionising. They penetrate moderatley far into materials before colliding and have a range in air of a few metres. They are abosorbed by a sheet of aluminium (around 5mm).
       • For every beta particle emitted, a neutron in the nucleus has turned into a proton.

4. Gamma Particle

   • Gamma rays are waves of electromagnetic radiation released by the nucleus.
     • They penetrate far into materials without being stopped and will travel a long distance through air.
       • This means they are weakly ionising because they tend to pass thriugh rather than collide with atoms. Eventually hit something and do damage.
         • They can be absorbed by thick sheets of lead or metres of concrete.