The intermolecular forces are the forces which mediate interaction between molecules which cause them to be attracted or repulsed by each other. Intermolecular forces are weak relative to intramolecular forces. Hence the intermolecular forces are known as the "weak bonds" or "secondary bonds". Attractive intermolecular forces are categorized into the following types:
- Hydrogen bonding
A hydrogen bond (often informally abbreviated H-bond) is a partial intermolecular bonding interaction between a lone pair on an electron rich donor atom, particularly the second-row elements nitrogen (N), oxygen (O), or fluorine (F), and the antibonding molecular orbital of a bond between hydrogen (H) and a more electronegative atom or group.
- Ionic bonding
The attraction between cationic and anionic sites is a non-covalent, or intermolecular interaction which is usually referred to as ion pairing or salt bridge. It is essentially due to electrostatic forces, although in aqueous medium the association is driven by entropy.
- Dipole–dipole forces
Dipole–dipole interactions are electrostatic interactions between molecules which have permanent dipoles. These interactions tend to align the molecules to increase attraction by reducing potential energy. A dipole–dipole interaction can be seen as the positive end of a polar molecule will attract the negative end of the other molecule and influence its position. Polar molecules have a net attraction between them. For examples, Hydrochloride (HCl) and Chloroform (CHCl₃).
- Dipole-induced dipole forces
An dipole–induced dipole force consists of a polar molecule and a non-polar molecule interacting. In a dipole–induced dipole force, the charge of the ion causes distortion of the electron cloud on the non-polar molecule
- Ion-dipole forces
An ion–dipole force consists of an ion and a polar molecule interacting. They align so that the positive and negative groups are next to one another, allowing maximum attraction.
- Ion–induced dipole forces
An ion–induced dipole force consists of an ion and a non-polar molecule interacting. Like a dipole–induced dipole force, the charge of the ion causes distortion of the electron cloud on the non-polar molecule.
- van der Waal forces
In chemistry, van der Waals' forces are a type of intermolecular force which is a relatively weak force that holds molecules together. Van der Waals' forces are the weakest type of intermolecular force. They are named after the Dutch scientist Johannes Diderik van der Waals (1837–1923). Negatively charged electrons orbit molecules or ions. The electrons create slightly different charges from one end of the molecule to the other. These slight differences are called partial charges, as δ- or δ+.
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