Editing Van der Waals force (section)

=== Force contributions ===
More broadly, [[intermolecular forces]] have several possible contributions. They are ordered from strongest to weakest:
# A repulsive component resulting from the [[Pauli exclusion principle]] that prevents close contact of atoms, or the collapse of molecules.
# Attractive or repulsive [[electrostatic]] interactions between permanent charges (in the case of molecular ions), dipoles (in the case of molecules without inversion centre), [[quadrupole]]s (all molecules with symmetry lower than cubic), and in general between permanent [[multipole]]s. These interactions also include [[hydrogen bond]]s, [[Cation–π interaction|cation-pi]], and [[Pi-Stacking (chemistry)|pi-stacking]] interactions. Orientation-averaged contributions from electrostatic interactions are sometimes called the [[Keesom force|Keesom interaction]] or Keesom force after [[Willem Hendrik Keesom]].
# Induction (also known as [[polarizability|polarization]]), which is the attractive interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes called [[Debye]] force after [[Peter J. W. Debye]]. The interactions (2) and (3) are labelled polar Interactions.
# Dispersion (usually named [[London dispersion force|London dispersion interactions]] after [[Fritz London]]), which is the attractive interaction between any pair of molecules, including non-polar atoms, arising from the interactions of instantaneous multipoles.

When to apply the term "van der Waals" force depends on the text. The broadest definitions include all intermolecular forces which are electrostatic in origin, namely (2), (3) and (4).<ref>{{cite web|url=https://www.ntmdt-si.com/resources/spm-theory/theoretical-background-of-spm/2-scanning-force-microscopy-(sfm)/22-cantilever-sample-force-interaction/224-the-van-der-waals-force/2241-intermolecular-van-der-waals-force|title=Intermolecular Van der Waals force|publisher=NT-MDT|accessdate=2024-05-30}}</ref> Some authors, whether or not they consider other forces to be of van der Waals type, focus on (3) and (4) as these are the components which act over the longest range.<ref>{{cite journal|first1=Jianmin|last1=Tao|first2=John|last2=Perdew|first3=Adrienn|last3=Ruzsinszky|title=Long range Van der Waals interaction|url=https://www.sas.upenn.edu/~jianmint/Publications/Papers/413180.pdf|journal=International Journal of Modern Physics B|volume=27|year=2013|issue=18 |pages=1330011–1330032 |doi=10.1142/S0217979213300119 |bibcode=2013IJMPB..2730011T }}</ref>

All intermolecular/van der Waals forces are [[anisotropic]] (except those between two [[noble gas]] atoms), which means that they depend on the relative orientation of the molecules. The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules. When molecules are in thermal motion, as they are in the gas and liquid phase, the electrostatic force is averaged out to a large extent because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Random thermal motion can disrupt or overcome the electrostatic component of the van der Waals force but the averaging effect is much less pronounced for the attractive induction and dispersion forces.

The [[Lennard-Jones potential]] is often used as an approximate model for the isotropic part of a total (repulsion plus attraction) van der Waals force as a function of distance.

Van der Waals forces are responsible for certain cases of pressure broadening ([[van der Waals broadening]]) of spectral lines and the formation of [[van der Waals molecule]]s.<!-- most use "Van der Waals molecules" ([http://pubs.acs.org/doi/abs/10.1021/cr00088a008], [http://www.wesleyan.edu/chem/faculty/novick/vdw.html], [http://doi.wiley.com/10.1002/anie.197204861], [https://books.google.com/books?id=PP6vtMJlWowC&pg=PA220]) few use "van" ([https://archive.today/20130202065320/http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFN-4CNJCXP-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1113973534&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=31e5934c994d877beafb7c335e513529], [http://www.infography.com/content/718688290900.html] (just a search aggregator)) --> The London–van der Waals forces<!-- see [http://www.clarkson.edu/projects/crcd/me437/downloads/5_vanderWaals.pdf] and [http://linkinghub.elsevier.com/retrieve/pii/S1672251507601560] --> are related to the [[Casimir effect]] for dielectric media, the former being the microscopic description of the latter bulk property. The first detailed calculations of this were done in 1955 by [[Evgeny Mikhailovich Lifshitz|E. M. Lifshitz]].<ref>{{cite web |url=https://www.sciencedaily.com/releases/2007/08/070806091137.htm |work=Science Daily |title=New way to levitate objects discovered |date=August 6, 2007}}</ref><ref>{{cite journal |doi=10.1088/1367-2630/9/8/254|title=Quantum levitation by left-handed metamaterials|year=2007|last1=Leonhardt|first1=Ulf|last2=Philbin|first2=Thomas G.|s2cid=463815|journal=New Journal of Physics|volume=9|issue=8|page=254|arxiv=quant-ph/0608115|bibcode=2007NJPh....9..254L}}</ref> A more general theory of van der Waals forces has also been developed.<ref>{{cite journal |last1=Dzyaloshinskii |first1=I. E. |last2=Lifshitz |first2=E. M. |last3=Pitaevskii |first3=Lev P. |title= General theory of van der Waals forces |journal= Soviet Physics Uspekhi|volume= 4|page= 153|year= 1961|doi= 10.1070/PU1961v004n02ABEH003330|bibcode=1961SvPhU...4..153D|issue= 2}}</ref><ref>{{cite journal |last1=Zheng |first1=Y. |last2=Narayanaswamy |first2=A. |s2cid=64619547 |title=Lifshitz Theory of van der Waals Pressure in Dissipative Media |journal=Physical Review A |volume=83 |issue=4 |page=042504 |year=2011|doi=10.1103/PhysRevA.83.042504 |arxiv=1011.5433 |bibcode=2011PhRvA..83d2504Z }}</ref>

The main characteristics of van der Waals forces are:<ref name="Sethi 1992">{{cite book | last1=Sethi | first1=M. S. | last2=Satake | first2=M. | title=Chemical bonding | publisher=Discovery Publishing House | publication-place=New Delhi | year=1992 | isbn=978-81-7141-163-4 | oclc=912437861 | page=}}</ref>

* They are weaker than normal covalent and ionic bonds.
* The van der Waals forces are additive in nature, consisting of several individual interactions, and cannot be saturated.
* They have no directional characteristic.
* They are all short-range forces and hence only interactions between the nearest particles need to be considered (instead of all the particles). Van der Waals attraction is greater if the molecules are closer.
* Van der Waals forces are independent of temperature except for dipole-dipole interactions.
In low molecular weight alcohols, the hydrogen-bonding properties of their polar [[hydroxyl group]] dominate other weaker van der Waals interactions. In higher molecular weight alcohols, the properties of the nonpolar hydrocarbon chain(s) dominate and determine their solubility.

Van der Waals forces are also responsible for the weak [[hydrogen bond]] interactions between unpolarized dipoles particularly in acid-base aqueous solution and between [[biomolecule|biological molecules]].