Question

which type of attractive force is present between the polar and non polar molecule

Answer 1

Detailed description

If the molecule is polar, it has areas of partial positive and partial negative charges which can interact with the areas of partial negative and partial positive charges in a second molecule (since opposites are attracted to each other). This type of force is called a dipole-dipole interaction. Hydrogen bonds are a special type of dipole-dipole interaction but are about five times stronger and thus are considered to be a distinct intermolecular force. Hydrogen bonds also involve the attraction of a partial positive atom in one molecule to a partial negative atom in a second molecule (and vice versa) but in this case the partial positive is a hydrogen atom which is VERY partial positive by virtue of the fact that it is covalently bonded to a small, electronegative atom (F, Cl, O, N). This VERY partial positive hydrogen atom will be VERY strongly attracted to the partial negative atom in the second molecule thus making the strongest intermolecular force, the hydrogen bond.

If the molecule is nonpolar, then no dipole-dipole interactions or hydrogen bonding can occur and the only possible intermolecular force is the weak van der Waals force. This force is sometimes called the induced dipole-induced dipole interaction since it involves the transient creation of an induced dipole within a nonpolar molecule due to the close proximity of the electron cloud of a second molecule. As soon as the second molecule moves away, the induced dipole disappears. While the induced dipole exists, that portion of the molecule is attracted to other molecules but as soon as the induced dipole disappears, the attraction also disappears. Thus this type of force is weak and short-lived and occurs between nonpolar molecules.