Covalent bonding

• Covalent compounds contain covalent bonds(which is a shared pair of electrons between atoms which are non-metals)
• When there are 2 or more atoms in a substance it is called a molecule. A diatomic molecule is when there are two atoms in that molecule. The elements involved in the bond may be the same e.g. Cl2 or different e.g. CO
• One single covalent bond is a sharing of 1 pair of electrons, two pairs of shared electrons between the same two atoms gives a double bond and it is possible for two atoms to share 3 pairs of electrons and give a triple bond
• Covalent compounds can be divided into two groups: Simple covalent molecules (Simple molecular), or Giant covalent molecules(Macromolecular/Giant molecular)
• Examples of simple covalent molecules are Cl2, H2, NH3, and H2O
• Examples of giant covalent molecules are diamond and graphite
• Many covalent substances exist as small separate molecules, with strong covalent bonds within the molecule, but weak Van der Waals' forces between them.
• Properties of small covalent molecules are:

  • Low melting and boiling point, they often exist as gases
  • They are poor conductors of electricity
  • Some will dissolve in water e.g. CO2 and NH3, while others will not e.g. iodine and sulphur
• Some covalent compounds exist as very large molecules. It is possible for many atoms to link up to form a giant covalent structure or lattice. The atoms are usually non-metals. This produces a very strong 3-dimensional covalent bond network or lattice
• Each carbon atom in diamond is covalent bonded to four other carbon atoms in a giant covalent structure. This symmetrical, tetrahedral arrangement of carbon atoms along with the covalent bond in all directions makes the structure very difficult to break.
• Properties of diamond:

  • One of the hardest naturally occurring substances, due to the large number of strong covalent bonds, which take a large amount of energy to break.
  • Very high melting point(3550°C) and boiling point(4827°C)
  • Insoluble in water
  • does not conduct electricity as there are no free electrons to carry charge
• Carbon can occur in the form of graphite. The carbon atoms form joined hexagonal rings forming layers 1 atom thick.

  There are 3 strong covalent bonds per carbon (3 C-C bonds in a planar arrangement from 3 or 4 of its 4 outer electrons)But, the fourth outer electron is delocalised or shared between all the carbon atoms

  The layers are only held together by weak intermolecular Van der Waals' forces, not by strong covalent bonds
• The properties of graphite are:

  • Very high melting(3696°C) and boiling(4827°C) point due to the many strong covalent bonds
  • Slippery with a soft feel due to the weak Van der Waals' forces between layers between layers
  • Conducts electricity due to to the carbon atoms having 1 delocalised electron that can move and carry charge
  • Insoluble in water
• The properties of graphene are:

  • High melting and boiling point, due to many strong covalent bonds, which take a lot of energy to break
  • Good conductor of electricity, 1 electron per carbon is delocalised and so is free to move and carry charge
  • Very strong, 100 times stronger than steel, due to the strong covalent bonds in the layers. It is also very light, the thinnest material possible and transparent, due to the layer being only one atom thick.
• Graphene is a third allotrope of carbon. It also has giant covalent structure. It is a very strong structure and it conducts electricity very well.
• Graphene is used for solar panels and batteries due to it being light, strong and a relatively inexpensive electrical conductor.
• Allotropes are different forms of the same state of an element