C2.1.4 - Covalent Bonding

• Describe Covalent Bonding

  A covalent bond is formed when two atoms share a pair of electrons. Covalent bonding occurs in most non-metal elements, and in compounds formed between non-metals.

  These shared electrons are found in the outer shells of the atoms. Usually each atom contributes one electron to the shared pair of electrons.

  The slideshow shows how a covalent bond forms between a hydrogen atom and a chlorine atom, making hydrogen chloride.

  
• Properties of Covalent Bonds

  • Covalent bonds between atoms are very strong
  • When two or more atoms are chemically bonded together, they form ‘molecules’
  • Covalently bonded substances may consist of small molecules or giant structures
  • Weak intermolecular forces exist between individual molecules
  • Shared electrons are called bonding electrons and occur in pairs
  • Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons (or lone pairs)
  • Simple covalent molecules do not conduct electricity as they do not contain free electrons
• Limitations of Models for Simple Covalent Molecules

  • Dot and Cross Diagrams
  • Advantages:
  • Useful for illustrating the transfer of electrons
  • Indicates from which atom the bonding electrons come from
  • Disadvantages:Fails to illustrate the 3D arrangements of the atoms and electron shells
  • Doesn’t indicate the relative sizes of the atoms

  
• • Ball and Stick Model
  • Advantages:
  • Useful for illustrating the arrangement of atoms in 3D space
  • Especially useful for visualizing the shape of a molecule
  • Disadvantages:
  • Fails at indicating the movement of electrons
  • The atoms are placed far apart from each other, which in reality is not the case as the gaps between atoms are much smaller

  
• • 2D Representations of MoleculesAdvantages:
  • Displayed formulae are 2D representations and are basically simpler versions of the ball and stick model
  • Adequately indicate what atoms are in a molecule and how they are connected
  • Disadvantages:
  • Fail to illustrate the relative sizes of the atoms and bonds
  • Cannot give you an idea of the shape of a molecule and what it looks like in 3D space