Resources written by Chas McCaw for sixth form chemistry teaching and beyond.
General interest:
Graphite Buckminsterfullerene Ice White phosphorus Benzene Cyclohexane AdamantaneCubic:
Sodium Caesium chloride Polonium Copper Halite Fluorite Antifluorite Zinc blende DiamondNon-cubic:
Hexagonal:
Magnesium WurtziteTetragonal:
RutileTrigonal:
α-quartzTriclinic:
Copper(II) sulfateOrthorhombic:
α-SulfurMonoclinic:
β-SulfurWithin each unit cell there is one full rotation of each of two alpha helices, which share a silicon atom at each end of the unit cell. Both of the alpha helices in the structure to the left are right-handed. Since the strand of each alpha helix has four silicon atoms in each cell, then with the passing from one silicon atom to the next there must be a rotation of 120 degrees. The structure is most easily visualised using a polyhedral approach and considering the chains of linked tetrahedra that result.
Go to page 4 to look at a polyhedral representation of this structure.