2.3 Simple Molecules & Covalent Bonds

• Covalent bonds

  Formed when pairs of electrons are shared between atoms
• Covalent compounds

  • Only non-metal elements participate in covalent bonding
  • Each atom gains a full outer shell of electrons, giving them a noble gas electronic configuration

  
• Molecules

  When two or more atoms are covalently bonded together
• Dot-and-cross diagrams

  • Used to show the electronic configurations in simple molecules
  • Electrons from one atom are represented by a dot, and the electrons of the other atom are represented by a cross
  • The electron shells of each atom in the molecule overlap and the shared electrons are shown in the area of overlap
  • The dot-and-cross diagram of the molecule shows clearly which atom each electron originated from

  
• When drawing dot-and-cross diagrams for covalent compounds, make sure that the electron shell for each atom is full (remember that the 1st shell can only hold 2 electrons)

  
• Single covalent bond (or single bond)

  Two adjacent atoms share one pair of electrons
• Common examples of simple molecules

  • Hydrogen
  • Chlorine
  • Water
  • Methane
  • Ammonia
  • Hydrogen chloride
• Double bond

  Two adjacent atoms share two pairs of electrons
• Triple bond

  Two adjacent atoms share three pairs of electrons
• Molecules with double and triple bonds

  • Nitrogen
  • Ethene
  • Methanol
  • Carbon dioxide