The Solid State

How do the salt crystals (left) from salt shaker and the larger crystals (right) compare to the atomic structure of NaCl below?  How would you describe  the arrangement of ions in NaCl?

How are the chloride ions arranged around the sodium ions or the sodium ions around the choride ions?

sodium ion at center                chloride ion at center

       

Each ion is octahedrally surrounded by the other ion in a very orderly or repeated fashion.  Hence NaCl is a crystalline solid.

Now view the structures of the two crystalline forms of carbon.  What is the hybridization of carbon in each structure?

       

spacefill                                                 spacefill

Which structure is more dense?  View in the spacefill mode and look at the packing of the atom carbons form all sides.

The carbon in diamond is tetrahedral (sp3) and trigonal planar in graphite (sp2).

           

The p orbital on the sp2 carbons in graphite allow for the electrical conductivity.  The sheets, held together by induced dipole interactions, allow for the layer to slip.

What about the packing of ions in an ionic solid like LiI or CsCl?

       

spacefill                                                     spacefill

Now view the structure of fullerine, C60.  Does the fullerine structure resemble diamond or graphite?  Why?  Describe the ring structure in fullerine?

  spacefill

Examine the structure of ice or solid water given below.  Does the structure resemble diamond or graphite?   Ice floats in liquid water.  View the structure in spacefill and explain why.

  spacefill

Each water molecule is tetrahedrally bound by hydrogen bonding to four other water molecules.  The structure is somewhat open making it less dense that its liquid.

        

Try your skills on these solids:

What is the force of attraction in solid carbon dioxide, dry ice?

What is the force of attraction in solid aluminum oxide, the mineral corundum? 

What is the force of attraction in solid iron or lead, which are good conductors of electricity in the solid?  Metals tend to have high densities.  Why?

iron                                                            lead

       

Scott A. Sinex           Prince George's Community College            November 2003