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Nature of Solids

Objectives:

    1.    Compare the properties of crystalline solids with those of amorphous solids.

    2.    For each type of solid, relate its structure and bonding to its properties.

Key Terms:

    crystalline solid        anhydrous        amorphous solid        covalent-network solid

Notes: (14-3)

Solids are very much like liquids in most ways varying mostly with regards to the internal movement of molecules (solids are fixed).  We can make all solids liquids, though, by increasing the internal kinetic energy to where it becomes stronger than the intermolecular forces keeping it as a solid.  Here are some additional comparative data:

  Like liquids, solids have high intermolecular forces that hold atoms and molecules in fixed positions.  
Solids, unlike liquids, have atoms and molecules in fixed positions
The density of most solids is only slightly greater than the liquid phase of the same material
A solid become liquid at its melting point

 

Crystalline Solids

A crystalline solid is one in which the molecules or atoms are arranged in highly ordered repeating patterns.

Most solids are crystalline
The smallest repeating unit is called a cell (think of a honey comb)
Some crystals exist as hydrates (having water molecules) - CuSO4 * 5 H2O (copper sulfate pentahydrate) has 5 water molecules included in each of its cells
Anhydrous crystalline solids are completely free of water

Amorphous Solids

Some solids do not form crystals and do not behave as solids.  These are called amorphous (without form).

plastic, rubber, glass
Covalently bonded

Bonding in solids:

The physical properties solids of substances are dependant mostly on the intermolecular bonds.

hardness
melting point
electrical conductivity
luster
fracture
tensile strength
malleability
ductile
Type of Solid Atoms Forces between particles Properties Examples
Metallic atoms Metallic bond Soft to hard, low to high melting point, electrical and thermal conductivity, malleable & ductile all metals
Molecular atoms or molecules Hydrogen bond, dipole-dipole, dispersion (temporary) soft, low to moderately high melting point, poor electrical and thermal conductivity most organic & inorganic compounds (methane, sugar, water)
Ionic Positive & negative ions electrostatic attractions Hard, brittle, high melting point, poor electrical and thermal conductivity ionic salts (NaCl, KBr, MgSO4)
Covalent-Network Covalent bonds covalent bond very hard, brittle, very high melting point, often poor electrical and thermal conductivity diamond, Silicon, quartz, graphite (all made from a non-metallic element)
 

 

 

 

 

 

 

 

Last modified: March 17, 2003