Atomic structure

• gold and carbon are two different elements
• an atom is the smallest particle of an element that still has its chemical properties
• a molecule is made from two or more atoms joined together, they are joined by attractive forces called chemical bonds
• example of a molecule?

  a carbon atom + two oxygen atoms = carbon dioxide molecule
• a size of an atom is given by its atomic radius (half its diameter)
• a bond length is the distance between the centres of two joined atoms
• Atomic radius and bond lengths are typically 10^−10m
• What is inside an atom?

  • protons and neutrons joined together as the nucleus at the centre
  • electrons, surrounding the nucleus in the shells
• subatomic particle relative mass relative charge

  proton 1 +1

  neutron 1 0

  electron 0.0005 -1
• The atomic number tells you the number of protons in its nucleus
• Each atom has an equal number or protons and electrons
• The mass number is the total number of protons and neutrons in an atom
• mass number = number of protons (atomic number) + number of neutrons
• number of neutrons = mass number - atomic number
• What are Isotopes?


  Atoms with the same number of protons and electrons but different number of neutrons, isotopes have the same atomic number but different mass number
• What are Ions?


  charged particles, they are formed when atoms or groups of atoms lose or gain electrons, this can happen during chemical reactions
• What did John Dalton do?

  • in 1803 he suggested all matter is made of atoms
  • discovered all atoms of an element are identical
  • different elements contain different types of atom
• What did J.J. Thomson discover?

  • in 1897 he discovered the electron
  • atoms are neutral overall
  • in his plum-pudding model he suggested atoms are spheres of positive charge with electrons dotted around
• Alpha particles

  • in 1909 Rutherford and two other scientists pointed beams of positively charged particles, called alpha particles at thin gold foil. They expected all the particles to go straight through the foil and not all did, some came straight back or changed direction slightly.
  • explanation - an atom has a positively charged nucleus contains most of its mass he also suggested that outside the nucleus, electrons orbit like planets
• What did Niels Bohr discover?

  In 1919 he used mathematical models to improve Rutherford's model. Bohr showed that electrons occupy fixed energy levels, or shells around the nucleus
• Development of the atomic model

  • Dalton - electron discovered
  • Thomson - nucleus discovered
  • Rutherford - mathematical model
  • Bohr - proton, then neutron discovered