chem chap 5.3 covalent substances

• simple covalent substances have low melting and boiling points


  a small amount of energy is required to overcome the weak intermolecular forces between the molecules. but during melting and boiling, strong covalent bonds between atoms are not broken
• simple covalent substances are insoluble in water but soluble in organic solvents
• both simple and giant covalent(except graphite) substances do not conduct electricity


  there are no free moving ions or electrons to conduct electricity
• Giant covalent structures

  • diamond
  • graphite
  • silicon dioxide (quartz & sand)
• Allotropes

  Different forms of the same element with different structural arrangements of atoms
• giant covalent structures have high melting and boiling points


  a large amount of energy is required to break the strong covalent bonds between a large number of atoms
• giant covalent substances are insoluble in water and organic solvents

  all atoms are held by strong covalent bonds so any force of attraction between giant molecular structure and solvent molecules are not strong enough to break the strong covalent bonds
• what is the structure of simple covalent substances?

  simple molecular structure
• what is the bonding of simple molecular structures?

  they have strong covalent bonds between atoms but weak intermolecular forces between molecules
• what is the state of simple molecular structures at rtp?

  liquid or gas
• what is the structure of giant covalent structures?

  giant molecular structure
• what is the bonding of giant covalent structures?

  there are strong covalent bonds between atoms
• what is the state of giant covalent structures at rtp?

  solid
• what are the structures of diamond and graphite?

  giant covalent structures
• hardness of diamond

  it is hard as the carbon atoms are arranged in a tetrahedral arrangement in a giant lattice structure, so it is difficult to break the strong covalent bonds.
• diamond has high melting and boiling points


  a large amount of energy is required to break the strong covalent bonds between the atoms in a giant molecular structure
• diamond does not conduct electricity


  all valence electrons of carbon atoms are used for bonding, so there are no free electrons that move through the structure
• uses of diamond


  tips of cutting, grinding and polishing tools
• hardness of graphite

  it is soft and slippery as the layers of carbon atoms are held loosely by weak intermolecular forces of attraction and can slide over each other when a force is applied
• graphite has high melting and boiling points


  a large amount of energy is needed to overcome the strong covalent bonds between atoms
• graphite conducts electricity

  each carbon atom has one valence electron not used for bonding, so these delocalised electrons can move along the layers from one carbon atom to another to help conduct electricity
• uses of graphite

  soft - pencil leads

  slippery - dry lubricant for machine parts

  fairly unreactive - inert electrodes
• what is the bonding of macromolecules(polymers)?

  there are strong covalent bonds between atoms but weak intermolecular forces between the molecules
• macromolecules(polymers) have no fixed melting/boiling points (low for polyethene)


  a small amount of energy is required to overcome the weak intermolecular forces of attraction between molecules
• macromolecules(polymers) do not conduct electricity in any state


  there are no mobile ions or electrons
• solubility of macromolecules(polymers)


  insoluble in water but soluble in organic solvents
• particles in macromolecules(polymers) in the solid state

  exists as chains of large molecules
• polyethene has low melting and boiling points


  there are weak intermolecular forces of attraction between the molecules