Editing Intermolecular force (section)

{{short description|Force of attraction or repulsion between molecules and neighboring particles}}

An '''intermolecular force''' ('''IMF'''; also '''secondary force''') is the force that mediates interaction between molecules, including the [[Electromagnetism|electromagnetic forces of attraction
or repulsion]] which act between atoms and other types of neighbouring particles (e.g. [[atom]]s or [[ion]]s). Intermolecular forces are weak relative to [[intramolecular force]]s – the forces which hold a molecule together. For example, the [[covalent bond]], involving sharing electron pairs between atoms, is much stronger than the forces present between neighboring molecules.<ref>{{Cite journal |last1=Fischer |first1=Johann |last2=Wendland |first2=Martin |date=October 2023 |title=On the history of key empirical intermolecular potentials |journal=Fluid Phase Equilibria |language=en |volume=573 |pages=113876 |doi=10.1016/j.fluid.2023.113876|bibcode=2023FlPEq.57313876F |doi-access=free }}</ref> Both sets of forces are essential parts of [[Force field (chemistry)|force fields]] frequently used in [[molecular mechanics]].

The first reference to the nature of microscopic forces is found in [[Alexis Clairaut]]'s work ''Théorie de la figure de la Terre,'' published in Paris in 1743.<ref>{{cite book | vauthors = Margenau H, Kestner NR | title=Theory of Intermolecular Forces |date=1969 |publisher=Pergamon Press |location=Oxford |isbn=978-0-08-016502-8 |edition=1st | series = International Series of Monographs in Natural Philosophy | volume = 18 }}</ref> Other scientists who have contributed to the investigation of microscopic forces include: [[Pierre-Simon Laplace|Laplace]], [[Carl Friedrich Gauss|Gauss]], [[James Clerk Maxwell|Maxwell]], [[Ludwig Boltzmann|Boltzmann]] and [[Linus Pauling|Pauling]].

Attractive intermolecular forces are categorized into the following types:
*[[Hydrogen bond]]ing 
*Ion–dipole forces and ion–induced dipole force
*[[Cation–π interaction|Cation–π]], σ–π and π–π bonding
*[[Van der Waals force]]s – [[Keesom force]], [[Debye force]], and [[London dispersion force]]
*[[Cation–cation bond|Cation–cation bonding]]
*[[Salt bridge (protein and supramolecular)]]

Information on intermolecular forces is obtained by macroscopic measurements of properties like [[viscosity]], [[PVT (physics)|pressure, volume, temperature]] (PVT) data. The link to microscopic aspects is given by [[virial coefficient]]s and intermolecular [[Pair potential|pair potentials]], such as the [[Mie potential]], [[Buckingham potential]] or [[Lennard-Jones potential]].

In the broadest sense, it can be understood as such interactions between any particles ([[molecule]]s, [[atom]]s, [[ion]]s and [[molecular ion]]s) in which the formation of chemical (that is, ionic, covalent or metallic) bonds does not occur. In other words, these interactions are significantly weaker than [[Covalent bond|covalent]] ones and do not lead to a significant restructuring of the [[electronic structure]] of the interacting particles. (This is only partially true. For example, all [[Enzyme|enzymatic]] and [[Catalysis|catalytic reactions]] begin with a weak intermolecular interaction between a substrate and an [[enzyme]] or a molecule with a [[Catalyst: Agents of Change|catalyst]], but several such weak interactions with the required spatial configuration of the active center of the enzyme lead to significant restructuring changes the energy state of molecules or substrate, which ultimately leads to the breaking of some and the formation of other covalent chemical bonds. Strictly speaking, all [[Enzyme catalysis|enzymatic reactions]] begin with intermolecular interactions between the [[Substrate (chemistry)|substrate]] and the enzyme, therefore the importance of these interactions is especially great in [[biochemistry]] and [[molecular biology]],<ref>{{Cite web |title=Biochemistry and Molecular Biology - Paperback - Despo Papachristodoulou, Alison Snape, William H. Elliott, Daphne C. Elliott - Oxford University Press |url=https://global.oup.com/ukhe/product/biochemistry-and-molecular-biology-9780198768111 |access-date=2024-01-04 |website=global.oup.com |language=en}}</ref> and is the basis of [[Enzyme|enzymology]]).