Chapter U2, Problem 3RE

Interpretation Introduction

Interpretation : Information provided by a molecular formula, structural formula and a ball- and- stick model are to be explained.

Concept Introduction :

Molecules are three dimensional. One can represent a molecule through its molecular formula, structural formula and a ball- and- stick model.

Explanation of Solution

Following are the information provided by:

• Molecular formula- It tells us the elements which are present in the molecule. It gives us information about the chemical composition of the compound. It describes how each molecule is formed. For example, the molecular formula for ethyl pentanoate is C₇H₁₄O₂. From this formula one can say that the molecule contains three types of atoms; carbon, hydrogen and oxygen. It has 2 oxygen atoms so it is a sweet smelling molecule.
• Structural formula- It tells us how the atoms are connected in a molecule, what bonds are present in the molecule and what isomers are possible. It also tells about the functional groups present in the molecule. Knowing this one can predict the molecular properties such as smell.
• Ball and stick model- It helps us in knowing the exact arrangement of atoms in space as well as the overall shape of the molecule. Even if the molecules have same functional groups; their shapes may vary. The ball and stick model shows the three dimensional arrangement of atoms in the molecule. The structural formula only gives a flat drawing of the molecule in which the atoms are arranged in a line. It does not represent the actual image of the molecule. From the arrangement of atoms in space one can predict the smell of the molecule. For example, in chiral, the carbon atoms are arranged in zigzag fashion.

The ball and stick model also tells us about the overall shape of the molecule. Molecules with same functional groups such as geraniol, menthol and fenchol differ in shape and hence differ in smell. In geraniol, the carbon atoms are connected in long chain whereas menthol and fenchol have ring structures.

Conclusion

The molecular formula describes how the molecule is formed. The structural formula of a molecule shows the molecule with the carbon atoms arranged in line whereas the ball and stick model shows the three dimensional structure of the molecule. This helps in better understanding the shape of the molecule and helps in predicting smell of the molecule.