Atomic Structure

• Atom


  Smallest part of an element
• Molecule


  Made of a fixed number of atoms covalently bonded together
• Atomic number


  Number of protons in atom
• Mass number


  The number of protons and neutrons in an atom
• Isotopes


  Atoms of the same element (same number of protons) but with a different number of neutrons
• Relative atomic mass


  Average mass of an atoms compared to 1/12th the mass of carbon-12
• Structure of atom


  • Central nucleus, composed of protons and neutrons
  • Surrounded by electrons, orbiting in shells (energy levels)
  • Atoms are neutral because the numbers of electrons and protons are equal
• Particle


  • Proton
  • Neutron
  • Electron
• Charge


  • 1
  • 0
  • 0 or 1/1836
• Calculation of relative atomic mass

  1. Multiply the mass of each isotope by its relative abundance

  2. Add them together

  3. Divide by the sum of the relative abundances (usually 100)
• Why some atoms are less reactive (e.g. lithium less reactive than potassium)

  lithium contains less outer shells than potassium

  outer shell of lithium is more strongly attracted to the nucleus

  therefore the electron is less easily lost