Question

In solid ${\mathbf{I}}_2$, is the distance between the two I nuclei of one molecule longer or shorter than the distance between two I nuclei of adjacent molecules? Explain.

Short answer

In ${\mathbf{I}}_2$solid the molecules are bonded by the strong covalent bond whereas in adjacent ${\mathbf{I}}_2$ molecules there is intermolecular forces that come into play which are weaker than a covalent bond.

Step-by-step solution

Covalent bond and Intermolecular forces

Covalent bonds are the bonds which are formed by thesharing of valence electronsof each atom involved in the bonding of the molecule. The bond is depending upon the valence electron of the atom which can be find out from the electronic configuration of an atom.

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is and induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

Molecule Interaction Explanation

I-atom belongs to group 17 which is called halogens and requires only 1 electron to fulfil its octet. In ${\mathbf{I}}_2$molecule, the I-atom need 1 electron which can be fulfilled by sharing of an electron to form a covalent bond which is a strong bond. But in adjacent ${\mathbf{I}}_2$ molecules, I-atom is an electronegative atom which interacts with the adjacent atom and forms an intermolecular interaction such as dipole-dipole interaction. Dipole-dipole Interaction: These interactions are the attractive forces which present in the polar molecules. Polar molecules have permanent dipoleswhich are produced by the presence of the opposite charge of the atom.

Now, the covalent bond is stronger than the intermolecular forces as it is formed by sharing of valence electron whereas the intermolecular forces are formed after the induced partial charges attraction on each atom.