A molecule is said to be polar if the bond electrons between the atoms in a covalent bond are unequally distributed, creating two ends. The electron redistribution is marked by showing the separation of charges as a partial charge above the atom's symbol. Therefore, a polar molecule always has a positive and a negative end resulting in a dipole. The pulling of bond electrons by an atom is attributed to its electronegativity.
Suppose atoms A and B participate in forming a polar covalent bond A-B and atom(A) tries to pull the maximum electron density from the atom(B). In that case, A is said to be more electronegative than B. Now several molecules of A-B interact by aligning their poles such that the opposite ends of the poles are together.
Many such electrostatic interactions happen across the medium by the orientation of the innate molecular poles leading to dipole-dipole attractive interactions. The force holding such polar molecules is also called the Keesom force and is the strongest of the three Vander Waal Force. Examples of polar molecules exhibiting van Der Waal Keesom force are HCl, HF, CO2, etc.
This is a supportive content for the chapter Intermolecular Forces part of CurlyArrows' Introduction to Organic Chemistry Course. Preview the Book.
Related Reading-
Difference between polar and nonpolar covalent bond
Introduction to Vander Waal Forces
