Solids and Intermolecular Forces:

Solid/Material
 
Attractive Force
Ionic: 
Made of up anions and cations.  These may either be simple ions like Na+ and Cl- or polyatomic ions, such as NH4+ and NO3- (NH4NO3).		 Electrostatic:  
Its the attraction between a positively charged cation and a negatively charged anion.  Note that the strength of attraction is based on Coulombs Law:  E = (K)(Q1)(Q2) / (r1 + r2).
Metallic: 
Consists of the elemental form of a metal or mixture of metals (an alloy)		 Non-directional Covalent Bonds: 
Metal atom positions are fixed and the valence electrons are allowed to move or flow between metal atoms.  Strength varies greatly with type of metal
Network: 
No discrete molecules.  Individual formula units are bonded to one another to form one large molecule.  Note that classification of a solid as a network solid assumes you have some prior knowledge of the solid state structure.  For our purposes,  a network solid will be one of the materials discussed in class or from the text.		 Covalent Bonds: 
These solids tend to be very hard particularly when a three-dimensional network of covalent bonds is present.   Two-dimensional or layered structures tend to be less rigid and are sometimes even lubricants.  The individual layers will then be held together by traditional intermolecular forces
Molecular: 
Made up of discrete molecules that are not bonded to each other through covalent bonds or electrostatic attractions ("ionic bonds").  Also includes elemental form of group 18 elements (noble gasses)		 Varies:
Attractive forces are dependent on nature of the molecule.  Must further classify the molecule (see below).  These materials will have the weakest intermolecular forces.
Type of Molecule
Intermolecular Force
Non-Polar London Dispersion Forces 
weak unless the molecule is large or heavy
Polar Dipole - Dipole 
Primary intermolecular force unless molecule is large.  It will also enhance IMF for large molecules.
Contains 
O-H, N-H or F-H bonds		 Hydrogen Bonding  
Strongest IMF for small molecules.  Added hydrogen bonds will increase IMF's

Solids Schematic 

In general, the strength of the various attractive forces are as follows:

1) Network solids will have the strongest attractive forces. (Covalent bonds are extremely strong)

2) Electrostatic attractions found in ionic solids are typically weaker than the covalent bonds in network solids. Ions with higher charges and smaller radii will have stronger attractions than other ions

3) Molecular solids have the weakest attractive forces (imf's):
the order among imf's is H-bonding > dipole-dipole > ldf

*Metallic solids have a wide range of strengths and can not be easily classified. While most metals are fairly hard (strong attractive forces), metals such as Hg, Na, and K have relatively weak attractions.

 

Some properties affected by intermolecular forces or interparticle attractive forces

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Created 02/02/99
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