2. Covalent bonding

• Molecules form when 2 or more atoms bond together. E.g. Cl2 , CO , H2O Molecules are held together by strong covalent bonds. Covalent bonds can be single, double or triple bonds.
• In covalent bonding, 2 atoms share electrons, so they’re both got full outer shell of electrons. Single covalent bond contains shred pair of electrons. Both positive nuclei are attracted electrostatically to shared electrons
• compounds that are made up of lots of individual molecules are called simple covalent compounds.
• Atoms in molecules are held together by strong covalent bonds, but molecules within simple covalent compound are held together by much weaker forces called intermolecular forces. They determine properties of simple covalent compounds. Have low melting and boiling points and are electrical insulators
• Giant covalent structures are type of crystal structure. Have huge network of covalently bonded atoms. (Sometimes called macromolecules structures )
• Carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with 3 bonds each. 4th outer electron of each carbon atom is delocalised. Sheets of hexagons are bonded together by weak van der Waals forces
• Graphites structure means it has certain properties:

  • Weak bonds between layers in graphite are easily broken, so sheets can slide over each other - graphite feels slippery and is used as dry lubricant and in pencils
  • Delocalised electrons in graphite are free to move along sheets, so an electric current can flow
  • Layers are quite far aware compared to length of Covalent bonds, so graphite has low density and is used to make strong lightweight sport equipment
  • Insoluble in any solvent. Covalent bonds in sheets are difficult to break
• Diamond is also made up of carbon atoms. Each carbon atom is covalently bonded to 4 other carbon atoms. Atoms arrange themselves in tetrahedral shape
• Because diamonds has its strong covalent bonds:

  • Diamond has very high melting point - sublimes at over 3800 K
  • Diamond Is extremely hard - used in diamond- tripped drills and saws
  • cant conduct electricity - all outer electrons are held In localised bonds
  • Diamond can’t dissolve in any solvent
• Co-ordinate bond / dative covalent bond, one of the atoms provides both of the shared electrons . E.g. Ammonium ion is formed by co-ordinate bonding. Forms when nitrogen atom in an ammonia molecule donates pair of electrons to proton (H+)
• Co-ordinate bonds form when one of the atoms in bond has lone pair of electrons, and other doesn’t have any electrons available to share.