Thursday, June 17, 2010

Molecular Models


Molecular models are often used to help explain the shape of molecules. In using the model we should remember that a model cannot represent fully the thing modeled, and it may ever mislead us if we imagine that the thing modeled must behave as predicted with model. Therefore we should know advantages and disadvantages of each model. There are many molecular models available. There of them are ball and stick, space filling and Dreiding models.

Ball and Stick or Tinkertoy Model

In this model atoms are represented as balls with certain colours. For examples: carbon is black, hydrogen is grey, nitrogen is blue, oxygen is red, and sulfur is yellow. The bond between two atoms is representend as a stick. Single bond is represented as a single stick. There are three advantages of this model. First, this model provides good three dimensional representational of molecules. Second, the number of bonds to each atom is correctly shown. Third, the bond lengths and bond angles are also correctly shown if the model is carefully made. The main disadvantage of this model is indicated with no overlap of electron clouds of the atoms forming the covalent bond. This may give an unfortunate idea of the "openness" of a molecule.

Space Filling Model

The basic units of this model are wooden spheres with certain colours from which parts have been cut of. When they are fitted together, they roughly represent covalent redii of the atom. The scale of the actual model is 1.00 cm = 1.00 Amstrong. The assembled model provides good three-dimensional representational of molecules and shows rather well bond angles and the relative sizes of the atoms forming covalent bonding compare to the ball and stick model. However, the number and the types of bonds to each atom is not shown.

Dreiding Model

This model is constructed of metal rod and tube joined together at a point that represent an atomic nuclei. The scale of this model is 1.00 cm = 0.40 Amstrong. This model provides good three-dimensional representation of molecules and shows quite precise relative size of bond lengths and bond angles in the molecules. There are two disadvantages of Dreiding Model. First, this model does not shown the three dimensional nature of atoms. Second, multiple bond is not represented. However, Dreiding model is often the favorite of research chemists because they represent so precisely the geometric relationship in molecules. So which type of model best represents the "true" structure of molecules? No model can exhibit all the characteristic of molecules. The remarkable fact is that molecular models have been so successfully used by chemists as they think about unseen and unseeable tiny molecules that make up all matter.

1 comments:

Megana Dal on June 17, 2010 at 7:58 PM said...

visiting u back! mind to have ex-links with me?

Acu Cinta Padamu, Friend! ;)

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