Difference Between Intermolecular Forces and Intra-molecular Forces

Intermolecular Forces vs Intra-molecular Forces
 

Intermolecular Forces

Intermolecular forces are the forces between neighboring molecules, atoms or any other particles. These can be attractive or repulsive forces. Attractive intermolecular forces hold substances together and, therefore, these are important to make bulk material. All the molecules have intermolecular forces between them, and some of these forces are weak, and some are strong. There are various types of intermolecular forces as follows.

• Hydrogen bond

• Ion- dipole forces

• Dipole- dipole

• Ion-induced dipole

• Dipole-induced dipole

• London/ dispersion forces

When hydrogen is attached to an electronegative atom like fluorine, oxygen or nitrogen, a polar bonding will result. Because of the electronegativity, the electrons in the bond will be more attracted to the electronegative atom than to the hydrogen atom. Therefore, hydrogen atom will get a partial positive charge, whereas the more electronegative atom will get a partial negative charge. When two molecules having this charge separation are close by, there will be an attraction force between hydrogen and the negatively charged atom. This attraction is known as hydrogen bonding. In some molecules, there can be charge separations due to electronegativity differences. Therefore, these molecules have a dipole. When an ion is close by, between the ion and the oppositely charged end of the molecule will form electrostatic interactions, which are known as ion-dipole forces. Sometimes, when the positive end of one molecule and the negative end of another molecule are close by, an electrostatic interaction will form between the two molecules. This is known as dipole dipole interaction. There are some symmetrical molecules like H₂, Cl₂ where there are no charge separations. However, electrons are constantly moving in these molecules. So there can be instant charge separation within the molecule if the electron moves toward one end of the molecule. The end with the electron will have a temporarily negative charge, whereas the other end will have a positive charge. These temporary dipoles can induce a dipole in the neighboring molecule and thereafter, an interaction between opposing poles can occur. This kind of interaction is known as an instantaneous dipole- induced dipole interaction. And this is a type of Van der Waals forces, which is separately known as London dispersion forces.

Intra-molecular Forces

These are the forces between the atoms of a molecule or compound. They bind atoms to each other and keep the molecule without breaking. There are three types of intra-molecular forces as covalent, ionic and metallic bonding.

When two atoms having similar or very low electronegativity difference, react together, they form a covalent bond by sharing electrons. Moreover, atoms can gain or lose electrons and form negative or positive charged particles respectively. These particles are called ions. There are electrostatic interactions between the ions. Ionic bonding is the attractive force between these oppositely charged ions. Metals release electrons in their outer shells and these electrons are dispersed between metal cations. Therefore, they are known as a sea of delocalized electrons. The electrostatic interactions between the electrons and cations are called metallic bonding.