Simple Molecular Substances

• Hydrogen

  • hydrogen atoms have just one electron
  • they only need one more to complete the first shell
  • so they often form single covalent bonds with another element or another hydrogen atom
• Oxygen

  • each oxygen atom needs two or more electrons to complete its outer shell
  • in oxygen gas two oxygen atoms share two pairs of electrons with each other making a double covalent bond
• methane

  • carbon has four outer electrons which is half a full shell
  • it can form four covalent bonds with hydrogen atoms to fill up its outer shell
• chlorine

  • each chlorine atom needs just one more electron to complete the outer shell
  • two chlorine atoms can share one pair of electrons and form a single covalent bond
• nitrogen

  • Nitrogen atoms need three more electrons
  • two nitrogen atoms share three pairs of electrons to fill their outer shells
  • this creates a triple bond
• water

  • the oxygen shares a pair of electrons with two H atoms to from two single covalent bonds
• hydrogen chloride

  • both atoms only need one more electron to complete their outer shell
• substances with covalent bonds usually have a simple molecular structure

  • molecules are held together by very strong covalent bonds but the forces of attraction between is very weak
  • to melt or boil - break these feeble intermolecular forces
  • gas or liquid at room temperature
  • as the molecule gets bigger the force increases therefore more energy is needed to break it
  • do not conduct electricity