covalent bonding

• covalent bonds form between non metallic atoms
• covalent substances with millions of atoms are called giant covalent structures.
• silicon dioxide (silica) is an example of a giant molevular structure
• 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.
• 1. Chlorine is a gas at room temperature.
  2. Bromine is a liquid at room temperature.
  3. Iodine is a solid at room temperature and gives off purple fumes. 
• why are different halogens different states at room temperature?

  The reason they 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. 
• state two properties of simple molecular substances.

  1. unable to conduct electricity
  2. low boiling points
• 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 multiple covalent bonds between each atom. 
• giant covalent structure have high melting points because all the atoms are held together by strong covalent bonds which require a lot of energy to break
• giant covalent structure

  
• summary of giant covalent structure

  1. Every atom is connected by strong covalent bonds 
  2. No weak intermolecular forces as there is only one structure
  3. High melting and boiling points
  4. Cannot conduct electricity (except graphite)
• summary of simple molecular structure

  1. Strong covalent bonds between the atoms of each molecule. 
  2. Weak intermolecular forces between molecules. 
  3. Low melting and boiling points (so normally gaseous as room temperature).
  4. Cannot conduct electricity. 
• properties of diamond


  1. strong
  2. high m and b points
  3. does not conduct electricity