Atomic Structure

• The plum pudding model 


  Cloud of positive with negative electrons stuck in it

  
• Atoms are very small, they have a radius of around 1 × 10-10 metres.
• Relative charge of protons is +1 and the relative mass is 1
• The Neutron has a charge of 0 and a relative mass of 1
• the electron has a charge of -1 and a relative mass of 0
• The total number of protons and neutrons is called the mass number and the number of protons is called the atomic number.
• Isotopes are forms of an element that have the same number of protons but different numbers of neutrons.
• • if the atom loses one or more electrons, it becomes a positively-charged ion
• • if the atom gains one or more electrons, it becomes a negatively-charged ion
• Normally, atoms are neutral. They have the same number of protons in the nucleus as they have electrons orbiting in the energy levels around the nucleus.
• An atom’s nucleus can only be stable if it has a certain amount of neutrons for the amount of protons it has.
• If the nucleus has too few neutrons, it will emit a ‘package’ of two protons and two neutrons called an alpha particle.
• If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron. This electron is called a beta (β) particle - this process is known as beta radiation.
• Alpha particles

   2 charge - 4 mass
• Beta particles

  0 mass - -1 charge
• Alpha penetrating power


  low - stopped by skin or paper
• Alpha particle range in air

  less than 5 cm
• Alpha particle ionising power


  high
• Beta particles penetrating power


  medium - stopped by 3mm aliminium
• Beta particles range in air


  1 meter
• Beta particle ionising power


  Low
• Gamma particle penetrating power

  high - stopped by lead / concrete
• Gamma particle range in air


  more than 1 kilometer
• Gamma particle ionising power


  Very low
• Half Life


  The time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
• irradiation

  exposing objects to radiation
• Uses for irradiation


  Sterilisation and beams of gamma rays kill tumours
• Contamination

  Occurs if an object has a radioactive material introduced to it
• Uses of contamination

  To check for leaks and tracers in medical settings
• Effects if radiation on the human body

  Can cause cancer and cause cataracts in eyes
• Backround radiation

  Radioactive materials occur naturally and, as a result, everyone is exposed to a low-level of radiation every day. This exposure comes from a mixture of natural and man-made sources.
• Nuclear fission


  The splitting of large nucleus into smaller nuclei
• The entire nucleus splits into two large fragments called 'daughter nuclei'. In addition to the 'daughter' products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions.
• Nuclear fusion


  Is when two small, light nuclei join together to make one heavy nucleus. Fusion reactions occur in stars where two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium isotope.