1. COVALENT NETWORKS GIANT MOLECULES MACROMOLECULES

2. COVALENT NETWORKS GIANT MOLECULES MACROMOLECULES They all mean the same!

3. DIAMOND, GRAPHITE and SILICA Many atoms joined together in a regular array by a large number of covalent bonds GENERAL PROPERTIES MELTING POINTVery high structures are made up of a large number of covalent bonds, all of which need to be broken if the atoms are to be separated. ELECTRICALDon’t conduct electricity - have no mobile ions or electrons but... Graphite conducts electricity STRENGTHHard - exists in a rigid tetrahedral structure Diamond and silica (SiO 2 )... but Graphite is soft GIANT (MACRO) MOLECULES

4. DIAMOND MELTING POINTVERY HIGH many strong covalent bonds must be broken to separate the atoms STRENGTHSTRONG and HARD each carbon is joined to four others in a rigid tetrahedral structure Coordination Number = 4 ELECTRICALNON-CONDUCTOR No free electrons - all four carbon electrons are used for bonding

5. GIANT (MACRO) MOLECULES GRAPHITE MELTING POINTVERY HIGH many strong covalent bonds must be broken to separate the atoms STRENGTHSOFT and SLIPPERY each carbon is joined to three others in a layered structure Coordination Number = 3 layers can slide over each other because they are held by weak van der Waals’ forces which can easily be broken. Layers can slide over each other so it can be used as a lubricant and in pencils ELECTRICALCONDUCTOR Only three of the carbon’s valence electrons are used for bonding which leaves the fourth to move freely along layers

6. GIANT (MACRO) MOLECULES DIAMONDGRAPHITE

7. SILICA SiO 2 MELTING POINTVERY HIGH many covalent bonds must be broken to separate the atoms STRENGTHSTRONG each silicon atom is joined to four oxygen atoms - C No. = 4 each oxygen atom are joined to two silicon atoms - C No = 2 ELECTRICALNON-CONDUCTOR - no mobile electrons