The term “INTERmolecular forces” is used to describe the forces of attraction BETWEEN atoms, molecules, and ions when they are placed close to each other
2 fév 2022 · central interest is the interplay between van der Waals forces and screening Now we describe our main result derived in the frame-
explain properties of liquids in terms of intermolecular about different types of van der Waals forces of molecules of the gas or in other words
in developing a theory to account for properties of real gases Van der waals forces include •London forces •Dipole - dipole forces
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75262_7963_TYPESOFINTERMOLECULARFORCES.pdf
TYPES OF
INTERMOLECULAR FORCES
byDr. Deepak ChoudharyAssistant ProfessorDepartment of Pharmaceutical Sciences,Mohanlal SukhadiaUniversity, Udaipur
Intermolecular forces may be attractive or repulsive. • Johannes D van derWaals, Dutch, was the first to postulate intermolecular forces in developing a theory to account for properties of real gases.
Van der waals forces include
•London forces •Dipole -dipole forces •Dipole -induced dipole forces
Other intermolecular forces are
•Ion -dipole interactions •Ion -induced dipole interactions •Hydrogen Bonding
LONDON FORCES
(DISPERSION FORCES) Thesearisefromtemporaryvariationsinelectrondensityinatomsandmolecules.At anyinstant,theelectrondistributionmaybeunsymmetricalandhenceproducean instantaneousdipole.Thiscancauseaninducedtransientdipoleintheneighboring moleculeandcausethemoleculestobeattracted. TheLondondispersionforceistheweakestintermolecularforce.TheLondon dispersionforceisatemporaryattractiveforcethatresultswhentheelectronsin twoadjacentatomsoccupypositionsthatmaketheatomsformtemporarydipoles. Thisforceissometimescalledaninduceddipoleinduceddipoleattraction.London forcesaretheattractiveforcesthatcausenonpolarsubstancestocondenseto liquidsandtofreezeintosolidswhenthetemperatureisloweredsufficiently.
DIPOLE -DIPOLE FORCES
Dipole-dipoleforcesareattractiveforcesbetweenthepositiveendofonepolar moleculeandthenegativeendofanotherpolarmolecule.Dipole-dipoleforceshave strengthsthatrangefrom5kJto20kJpermole.Theyaremuchweakerthanionicor covalentbondsandhaveasignificanteffectonlywhenthemoleculesinvolvedare closetogether(touchingoralmosttouching).
INDUCED -DIPOLE FORCES
Ion -induced dipole forces
Anion-induceddipoleattractionisaweak
attractionthatresultswhentheapproachofan ioninducesadipoleinanatomorinanonpolar moleculebydisturbingthearrangementof electronsinthenonpolarspecies.
Dipole-InducedDipoleForces
Adipole-induceddipoleattractionisaweak
attractionthatresultswhenapolarmolecule inducesadipoleinanatomorinanonpolar moleculebydisturbingthearrangementof electronsinthenonpolarspecies.
HYDROGEN BOND
Thehydrogenbondisaspecialdipole-dipoleinteractionbetweenthehydrogen atominapolarN-H,O-HorF-HbondandanelectronegativeO,NorFatom.
A-H----BorA-H----A
AandBareO,NandF