Types of Covalent Structures

• Atoms can share electrons to form covalent bonds.

  Covalent substances that only contain a few atoms are called simple molecular substances. 

  On the other hand, covalent substances with millions of atoms are called giant covalent structures.
• • In simple molecular substances, the individual molecules are held together by intermolecular forces that exist between the molecules. 
  • These intermolecular forces are weak and so don't require very much energy to break.
  • This means that they can be broken at relatively low temperatures. As a result most simple molecular substances exist in the gaseous state at room temperature.
• Diamond and graphite are both made from the element carbon, and are examples of giant covalent structures.

  Their atoms are arranged in a regular repeating lattice structure with many multiple covalent bonds between each atom. 
• properties of diamond:

  • does not conduct electricity
  • strong
  • high melting and boiling points
• Chlorine is a gas at room temperature
• Bromine is a liquid at room temperature.
• Iodine is a solid at room temperature and gives off purple fumes. 
• • The reason different halogens are in different states at room temperature is that they have different melting and boiling points.
  • As you go down group 7, the atoms (and thus molecules) get larger. This means there will be more intermolecular forces, and so more energy (and a higher temperature) will be required to break them
•  properties of simple molecular substances:

  • Unable to conduct electricity
  • low boiling points
• Giant covalent structures have high melting points, as the atoms are all held together by strong covalent bonds which require a large amount of energy to break