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A-Level化学-物质Substances and Their Structure

  Revision: Substances and their Structure and Properties

  Carbon

  Diamond

  Structure - Each carbon atom is covalently bonded to another 4 carbon atoms which forms up a tetrahedral shape which repeats itself throughout the macromolecule.

  Melting point - The Melting point of diamond is 3820 degrees Kelvin which is extremely high and this is because of the multiple strong covalent bonds throughout the molecule. Density - The density of diamond is 3.52g/cm3

  Electrical conductivity - Diamond does not conduct electricity.

  Graphite

  Structure - Each carbon atom is covalently bonded to another 3 carbon atoms which forms up different planes which are joined by weak intramolecular forces. There is a "sea" of delocalized electrons between the layers.

  Melting point - The Melting point of graphite is 3652 degrees kelvin which is extremely high and this is because of the multiple strong covalent bonds throughout the molecule.

  Density - The density of graphite is 2.09g/cm3

  Electrical conductivity - Graphite is a very good electrical conductor because of the sea of delocalized electrons.

  Ice

  Structure - Each Ice molecule forms up a regular hexagonal lattice out of water molecules which bond to each other through hydrogen bonding between a hydrogen and a lone pair of electrons on an oxygen. Ice can form up 9 other structural forms at different temperatures and pressures. At normal pressures it can also form up a structure similar to diamond.

  Melting point - The Melting point of Ice is 273 degrees kelvin which is low because the hydrogen bonds are weak.

  Density - The density of Ice is 0.93g/cm3, which is less than water's 1.00g/cm3. This means ice floats.

  Electrical conductivity - Ice does not conduct electricity.

  Sodium Chloride

  Structure - Sodium chloride forms crystals with cubic symmetry. In these, the larger chloride ions, shown to the left as yellow spheres, are arranged in a cubic close-packing, while the smaller sodium ions, shown to the left as blue spheres, fill the octahedral gaps between them. Each ion is surrounded by six of the other kind. This same basic structure is known as the halite structure. It is held together with an ionic bond and electrostatic forces.

  Melting point - The Melting point of NaCl is 1074 degrees kelvin due to the strong electrostatic forces.

  Density - The density of graphite is 2.16g/cm3

  Electrical conductivity - Sodium chloride only conducts electricity in the molten or aqueous state where the ions are free to move.

  Iodine

  Structure - Each Iodine atom bonds covalently to another to form an I2 molecule. These I2 molecules then bond to each other through weak inter-molecular bonds. In solid iodine the molecules are arranged in waves as shown right.

  Melting point - The Melting point of Iodine is 386 degrees Kelvin.

  Density - The density of Iodine is 4.94 g/cm3.

  Electrical conductivity - Iodine does not conduct electricity.

  Polythene

  Structure - Polythene is a giant covalent structure formed from polymerization of ethene. This forms up very long chains which then lay down into two regions, amorphous regions (A) and crystalline regions (B) The amount of each type of region varies and causes different properties.

  Melting point - The Melting point of polythene is ~388-408 degrees kelvin.

  Density - The density of Polythene is 0.91-0.97g/cm3.

  Electrical conductivity - Polythene does not conduct electricity.