Bonding

• Ion


  An electrically charged atom or group of atoms formed by the loss or gain of electrons
• Negative ions (anions)


  Form when atoms gain electrons, meaning they have more electrons than protons
• Positive ions (cations)


  Form when atoms lose electrons, meaning they have more protons than electrons
• Ionic bonds


  The positive and negative charges are held together by the strong electrostatic forces of attraction between oppositely charged ions
• Dot and cross diagrams


  • A simple and quick way to show the formation of an ionic compound
  • The electrons from each atom should be represented by using solid dots and crosses
  • If there are more than two atoms, then hollow circles or other symbols / colours may be used to make it clear
  • The large square brackets should encompass each atom and the charge should be in superscript and on the right-hand side, outside the brackets
  • For larger atoms with more electron shells, only the valence shell needs to be drawn
• Lattice structure


  Formed by ionic compounds, consisting of a regular arrangement of alternating positive and negative ions tightly packed together
• Ionic compounds


  • Strong electrostatic forces of attraction present between oppositely charged ions, holding the lattice together
  • Electrostatic forces are strong, acting in all directions - they form the basis of ionic bonding
  • As a result of so many electrostatic forces existing in this lattice structure, ionic compounds have high melting and boiling points
• Ionic lattice structure


  • Exists in three dimensions which allows solid ionic compounds to form regular shapes
  • Solid ionic crystals contain huge numbers of ions and so are referred to as giant ionic lattices
  • Ions are incredibly small - a single grain of sodium chloride contains trillions of sodium and chloride ions - so models are used to represent the structure of the ionic compound