Question

Explain how molecular models may be used to represent a range of molecules of different shapes.

Answer 1

Solution:

There are broadly three molecular models namely, ball-and-stick, space filling, and skeletal, are used to represent the molecular shapes.

a. Ball-and-stick model:

• This is a molecular model of molecules which displays the 3D position of both, the atoms and the bonds between the atoms.
• The atoms are typically represented by spheres. The chemical element of each atom is often indicated by the sphere's color.
• The spheres are connected by rods which represent the bonds. Double and triple bonds are usually represented by two or three curved rods, respectively. Alternately the σ and π bonds are represented by correctly positioned sticks.
• The angles between the rods should represent the angles between the bonds.
• The distances between the centers of the spheres should be proportional to the distances between the corresponding atomic nuclei.

b. Space filling model:

• This model is also known as a calotte model, is a type of 3D molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms.
• Center-to-center distances are proportional to the distances between the atomic nuclei, all in the same scale.
• Atoms of different chemical elements are usually represented by spheres of different colors.

c. Skeletal model:

• This model of a molecule is a type of molecular structural formula that serves as a shorthand representation of a molecule's bonding and some details of its molecular geometry. Hence, it is also called as shorthand formula line-angle formula or line-angle formula.
• It is represented in 2D, as on a piece of paper. It employs certain conventions to represent carbon and hydrogen atoms, which are the most common in organic chemistry.
• A skeletal formula shows the skeletal structure (skeleton) of a molecule.