S-Cool Revision Summary

S-Cool Revision Summary

Atoms are made up of:

  • protons;
  • electrons;
  • neutrons.

Protons and neutrons are in the nucleus and the electrons orbit the nucleus. Protons have a positive charge, electrons have a negative charge and neutrons have no charge. The shape of the atom was discovered using the alpha-scattering experiment. This showed the original plum-pudding model to be wrong!

Atomic notation is used to describe atoms. The top number is the mass or nucleon number. It tells us how many protons and neutrons there are in the nucleus. The bottom number is the proton or atomic number, which tells us how many protons are in the nucleus. During reactions the total number of protons and neutrons must stay the same.

Isotopes of an element have the same number of protons but a different number of neutrons in the nucleus. It is this different number of neutrons that makes some isotopes unstable and radioactive. These isotopes are called radioisotopes.

Ionisation is where an electron is removed from a neutral atom, leaving the atom with a positive charge.

Radiation causes ionisation. This can be used to detect radiation, as the amount of ionisation can be measured with a Geiger-Muller tube.

Ionisation can damage or kill living cells, this can cause cancer to develop.

Alpha particles, beta particles and gamma waves are the three main types of radiation emitted during radioactive decay. All three types of radiation are emitted from the nucleus of the atom.

When radiation is emitted the unstable atom loses energy to become more stable. If alpha or beta particles are emitted, new elements are formed because of the change in the number of protons in the nucleus.

Alpha, beta and gamma radiation all behave slightly differently due to the way they are made up. Alpha ionises the most over a small distance but is not very penetrating. Gamma is the most penetrating but ionises less over the same distance.

Decay equations can be used to work out what new daughter element will be produced when radioactive decay takes place.

Safety precautions must be taken when handling radioactive substances. These include, using long handled tongs, pointing sources away from people, wearing lead lined clothing, not inhaling or eating sources.

The half-life of a substance is the time it takes for half of the original parent atoms to decay. It is also the time it takes for the count rate of a substance to fall to half the original value.

Radiation is used in medicine to cure cancer, in industry to detect the thickness of materials and in dating.

Background radiation is radiation that is produced around us all of the time. Sources include certain rocks, cosmic radiation, radon gas in the air, nuclear waste and experiments, medical uses and some foods. The background radiation needs to be subtracted from experiment results on radioactivity.