covalent bonding and substances

• what do covalent bonds do ?

  share electrons
• describe this covalent bond

  A) ammonia

  B) nitrogen has five electrons in its outer shell

  C) nitrogen needs 3 more electrons in the shell

  D) 3 covalent bonds made with hydrogen

  
• describe the covalent bond

  A) methane

  B) carbon atom has 4 electrons in its outer shell

  C) the carbon atom needs 4 more electrons shared

  D) 4 covalent bonds shared between carbon and hydrogens

  
• what is it called when 2 pairs of electrons are shared ?

  Double bond
• what two things can substances containing covalent bonds be ?

  simple molecules and giant structures
• what are the 3 types of giant covalent structures ?

  Diamond, graphite, and C60 fullerene.
• what are simple molecular compounds made up of ?

  a few atoms covalently bonded together
• do simples molecular compounds have low or high melting and boiling points ?

  low
• explain why simple molecular substances have low melting and boiling points

  A) strong covalent bonds

  B) weak intermolecular forces

  C) weak intermolecular forces low melting boiling points

  
• explain why simple molecular substances have low melting and boiling points ?

  since there are weak intermolecular forces of attraction between bonds the molecules are easily seperated showing how the substances will have low melting and boiling points
• intermolecular forces are stronger between molecules with a high relative molecular mass than between smaller molecules
• describe diamond ?

  • made up of of a network of carbon atoms that each form 4 covalent bonds
  • strong covalent bonds take lots of energy to break so diamond has a high melting and boiling point
  • does not conduct electricity because it has no free electrons or ions
• describe carbon ?

  • each carbon atom only forms 3 covalent bonds creating layers of carbon atoms
  • layers held together by weak intermolecular forces so are free to slide over each other
  • soft and slippery
  • graphite has a high melting and boiling point because the covalent bonds need loads of energy to break
  • since it has 1 delocalised electron, graphite conducts electricity
• describe C60 fullerene ?

  • the molecules are hollow spheres made up of 60 carbon atoms
  • made up of large covalent molecules
  • molecules held together by intermolecular forces so they cans lide over each other
  • material is soft
  • it has 1 delocalised electron but electrons cant move between the molecules so it is a poor conducter of electricity