The Four Types of Solids

Covalent Networks (Wikipedia Link)
  • Atoms are connected in long chains by covalent bonds.
  • Recall: Covalent bonds occur when two atoms share electrons and are very strong.
  • Because it takes a lot of energy to break covalent bonds, these solids have very high melting points (Ever see a diamond melt?)
  • Examples of covalent networks include diamond, graphite and quartz.
Metals (Wikipedia Link)
  • Metals are considered to have a different structure: Atoms arranged symmetrically, with a sea of electrons floating around them.
  • We assume the electrons are mobile around the atoms because metals conduct electricity so well.
  • Because there is no polarity or direction to the solid, it's easier to melt (the metal mercury (Hg) is a liquid at rom temperature!) and usually ductile (easily made into wire).
  • Examples are obvious: aluminum, copper, gold, sodium...
Ionic Solids (Wikipedia Link)
  • Positive and negative ions are held together by ionic bonds - the attraction between positively- and negatively-charged ions.
  • These bonds are tough to break as well, so ionic solids have high melting points and low vapour pressures.
  • Because the electrons are held tightly by the negative ions, these solids do not conduct electricity.
  • They are soluble because they are made of ions, and so are easily dissolved by polar water molecules.
  • Examples include sodium chloride (table salt) and calcium carbonate (chalk).
Covalent Solids (aka Molecular Solids) (Wikipedia Link)
  • These are solids formed when individual covalent (molecular) molecules freeze.
  • Water, methane, carbon dioxide, sugar (glucose, sucrose), and octane molecules have a distinct chemical formula and are made of individual molecules, which form a "covalent (molecular) solid" when frozen.
  • These solids are held together by Intermolecular Forces (dipole-dipole forces, London dispersion forces, hydrogen bonds)