Atomic Structure

• Atoms

  • Incomplete outer shell of electrons
  • Need a full outer shell to be stable
  • Gain or lose electrons to achieve a full outer shell
• Arranging electrons in atoms

  1. Draw nucleus

  2. Add electrons to shells in order

  3. Fill shells clockwise

  4. Outer shell needs to be full for stability
• Stable atom


  Has a full outer shell of electrons
• Unstable atom


  Does not have a full outer shell of electrons
• Noble gases have completely full outer shells and do not react
• Determining electron arrangement


  1. Find atomic number

  2. Draw shells

  3. Fill shells with electrons
• Ion


  Atom that has lost or gained electrons, resulting in an overall charge
• Calcium ion


  • 2,8,8
• Fluoride ion


  • 2,7
• Ions are drawn with square brackets around them and the charge in the top right
• Group seven elements


  • Fluorine
  • Chlorine
  • Bromine
  • Iodine
  • Astatine
  • Tennessine
• Halogens


  • Fluorine is a poisonous yellow gas and very reactive
  • Chlorine is less reactive and a poisonous green gas
  • Bromine is a ready brown volatile liquid and poisonous
  • Iodine is a dark gray solid that can form poisonous purple vapors, but is also an antiseptic
• Astatine and Tennessine can be ignored as they don't really come up in the course
• Diatomic molecules


  Two atom molecules formed by halogens sharing electrons and forming covalent bonds
• Simple molecular structures


  Compounds formed by halogens forming covalent bonds with other non-metals such as hydrogen or carbon
• As you go down the halogen group

  Melting and boiling points increase, reactivity decreases
• Halides


  The name given to halogen ions when they gain an electron to form a 1- ion
• Halides


  • Fluoride
  • Chloride
  • Bromide
  • Iodide
• Displacement reactions


  More reactive halogens displace less reactive ones
• Noble gases


  • Colorless gases
  • Inert (don't react)
  • Exist as single atoms
  • Non-flammable
• As you go down the noble gas group


  Boiling points increase
• For questions involving halogen displacement reactions, you will often be asked about the colour changes that take place. 

  The key information to remember is:

  • Halide salts (e.g. KCl, KBr, KI) are colourless
  • Bromine water is orange
  • Chlorine water is colourless
  • Iodine water is brown