Question

How can you tell if dipole-dipole forces are present?

Answer 1

Dipole-dipole interaction is a type of intermolecular force. It includes attraction of a partial positive charge to a partial negative charge and thus an attraction force works between them. We can find dipole-dipole interaction in every polar compound. Polar molecules contain polar bonds dipoles. To determine whether a bond is polar, you look at the electronegativity difference between the atoms.

Complete step-by-step answer:
We know that there are certain forces that play in between the molecules in a compound. These forces play a role of binding force i.e. is responsible for keeping the molecule intact. There are also some forces that act between two compounds bringing them together by the means of weak attraction force. They are called the intermolecular forces.

Now let us discuss this interaction. Dipole-dipole interaction is one of these forces and it is attractive in nature. It is basically the force between the positive end and the negative end of two polar compounds and is responsible for forming a weak attraction between the two polar compounds. Dipole-dipole interaction arises due to partial positive charge on one polar compound which is attracted to the partial negative charge on another molecule of the polar compound. Every polar molecule shows dipole-dipole interaction. For example let’s take hydrochloric acid. Here the positive end is the hydrogen atom and it has a partial positive charge and chlorine atom is the negative end and it has a partial negative charge.

To be considered a polar bond, the difference in electronegativity must be large. The dipole moment points in the direction of the vector quantity of each of the bond electronegativity are added together. London dispersion force is a weaker intermolecular than dipole-dipole interaction. For example, in water, the centre of positive charge is halfway between the two hydrogens. The shape of the molecule plays a role in whether the molecule contains dipole-dipole forces

Note: There are other such forces like London dispersion force, Van der Waals force and even hydrogen bonding. Hydrogen bonding is the strongest intermolecular force. Van der Waals forces are of two types: London dispersion force and dipole- dipole interaction.