Basic Ideas about Atoms

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  • Created by: Becky
  • Created on: 20-04-13 09:45

Atomic Structure

Each atom contains protons, neutrons and electrons

Protons are positive, neutrons have no charge and electrons are negative

Atomic number - tells you the number of protons in the nucleus

Mass number - tells you the number of protons and neutrons in the nucleus

Isotope - an element with the same number of protons and electrons and a different number of neutrons


Lead is the largest stable nucleus, anything with a larger nucleus then lead are not stable

There are 3 types of radiation:

  • Alpha - consists of 2 protons and 2 neutrons. It has a low penetrating power (is stopped by paper), it has a small deflection towards the the negative plate in a field and its ionising power is high.
  • Beta - consists of an electron from the nucleus. It has medium penetrating power (is stopped by an aluminium plate), in a field it has a large deflection towards the positive plate and its ionising power is medium.
  • Gamma - is a high energy electromagnetic wave. It has a high penetrating power ( is stopped by a thick lead plate), in a field it has no deflection and its ionising power is low.


Definition - one element turns into another by emitting alpha and/or beta particles

  • Emits alpha - lose 2 protons and 2 neutrons from the nucleus. The atomic number goes down 2 and the atomic mass goes down 4
  • Emits beta - lose 1 electron from nucleus but a neutron turns into a proton. The atomic number goes up 1 and the atomic mass stays the same

Half life

Definition - time taken for half the mass of the material to decay.

Questions are either about the time taken for the radioactivity of a sample to fall to a certain amount or to find the mass of a substance remaining after a certain amount of time.


The high energy break chemical bonds in cells giving rise to changes in DNA which causes mutations. This leads to cancer at lower dose of radiation or death at higher doses of radiation.


  • Medicine : Cobalt - 60 in radiotherapy. Iodine - 131 acts a tracer in patients with


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