Covalent Bonding

• Covalent bonds are formed when atoms share electrons
• Dot and cross diagram

  Diagram showing shared electrons in a covalent bond, with dots representing electrons from one atom and crosses representing electrons from another atom
• Tetrahedron shape


  • The shape of the CH4 (methane) molecule, important in organic chemistry
• Double bond


  A covalent bond where 4 electrons are shared between two atoms
• Triple bond


  A covalent bond where 6 electrons are shared between two atoms
• Dative covalent bond


  A covalent bond where both shared electrons come from the same atom, resulting in a positive charge
• Dative covalent bonds are not very common, the example of NH4+
• Factors affecting covalent bond strength

  • Bond length - shorter bonds are stronger
  • Number of bonds - multiple bonds are stronger than single bonds
• Dative bond


  Also known as a coordinate bond
• Electronegativity


  The tendency of an atom to attract a bonding pair of electrons
• Fluorine has the highest electronegativity
• Electronegativity trends


  • Increases across a period from left to right
  • Decreases down a group
• Polar molecule


  A molecule where one end is slightly negative and the other slightly positive due to unequal sharing of electrons
• H2O is an example of a polar molecule
• Electronegativity difference


  • 0 - pure covalent bond
  • 0.4 - 2 - polar molecule
  • Greater than 2 - ionic bond