Atomic structure

  • Created by: holly6901
  • Created on: 10-05-19 12:28
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  • Atomic structure
    • Atomic model
      • An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.
      • Atoms are very small and have a radius of about 1 × 10-10 metres.
      • The electrons are arranged at different distances from the nucleus (different energy levels).
      • The radius of a nucleus is less than 1/10 000 of the radius of an atom.
      • Most of the mass of an atom is concentrated in the nucleus.
    • Subatomic particles
      • Protons have a relative charge of +1.They are found in the nucleus.
        • An element’s atomic number is the number of protons it possesses.All atoms of the same element have the same number of protons.
      • Electrons have a relative charge of -1.They are found in fixed orbits around the nucleus.
        • In any atom, the total number of negative electrons equals the number of positive protons, meaning atoms have no overall electric charge.
      • Neutrons have a relative charge of 0 - they are neutral.Like protons, they are found in the nucleus.
    • Rutherford's experiment
      • Most alpha particles passed straight through the foil.This suggested that most of the atom is made up of empty space.
        • However, some particles bounced back towards the source.
      • The large deflections suggested that some positively charged mass in the atom was repelling the particles.
      • This led to the model of the atom with negatively charged electrons orbiting a positively charged nucleus.
    • Models of the atom
      • In 1897, an English physicist called J. J. Thomson discovered electrons.
        • He modelled the atom as a 'plum pudding' - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the 'dough'.
      • In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
        • He concluded that an atom's mass is concentrated in the atom's centre. This was called the "nucleus" and it contained positively charged particles called protons.
      • Neils Bohr discovered that electrons orbit (fly around) the nucleus at fixed distances.
      • In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.
    • Electron arrangements
      • When atoms absorb electromagnetic radiation, electrons move to a higher energy level further away from the nucleus.
      • When atoms emit electromagnetic radiation, electrons can drop to a lower energy level, closer to the nucleus.
    • Ions
      • Atoms turn into positive ions if they lose one or more outer electrons.
      • In an atom, the number of electrons is equal to the number of protons in the nucleus.Atoms have no overall electrical charge
      • Atoms turn into negative ions if they gain one or more electrons.
    • Isotopes
      • Protium is a hydrogen atom with 1 proton and 0 neutrons.99.98% of hydrogen atoms are protium.
        • It is used in hydrogen fuel cells and the production of plastics.
      • Deuterium is a hydrogen atom with 1 proton and 1 neutron.Around 0.02% of hydrogen atoms are deuterium.
        • It is used in nuclear fusion.
      • Tritium is a hydrogen atom with 1 proton and 2 neutrons.It is very rare.
        • It is used in thermonuclear fusion weapons.
      • Isotopes are forms of an element that have the same number of protons, but a different number of neutrons.
      • A nuclide is a type of isotope.A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons.


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