Detailed

• Atoms


  The smallest part of an element that can exist
• Chemical symbols


  Represent an atom of an element e.g. Na represents an atom of sodium
• Compounds


  Formed from elements by chemical reactions, contain two or more elements chemically combined in fixed proportions, can be represented by formulae
• Mixtures


  Consist of two or more elements or compounds not chemically combined, can be separated by physical processes
• Development of the model of the atom

  1. First thought to be tiny spheres

  2. Discovery of electron led to plum pudding model

  3. Alpha particle scattering experiment led to conclusion mass concentrated in nucleus

  4. Bohr suggested electrons orbit nucleus at specific distances

  5. Later experiments showed positive charge subdivided into protons

  6. Chadwick's work provided evidence for neutrons
• Atomic number


  The number of protons in an atom of an element
• All atoms of a particular element have the same number of protons
• Atoms of different elements have different numbers of protons
• Relative charge of subatomic particles

  • Proton: +1
  • Neutron: 0
  • Electron: -1
• An atom has an overall charge of 0, so number of protons = number of electrons
• Size and mass of atoms

  • Atoms are very small, radius about 0.1 nm, nucleus radius less than 1/10,000 of atom but holds almost all mass
  • Relative mass: Proton 1, Neutron 1, Electron very small
• Mass number


  Sum of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Calculating relative atomic mass

  1. Take account of abundance of isotopes

  2. Example: ((14 x 20) + (12 x 80)) / 100 = 12.4
• Electronic structure


  • Electrons occupy lowest available energy levels (shells closest to nucleus)
  • Example for sodium: 2,8,1