Intermolecular forces (IMF)


Fig. 11.1a: energy diagram showing states that water and the step transitions between these states.
You should currently be acquainted with the 6 step transitions described in number 11.1a Melting: The change from the solid to the liquid phase Freezing: The transition from the liquid phase to the solid phase Evaporating: The shift from the liquid phase to the gas phase Condensing:The change from the gas phase to the liquid phase Sublimation: The shift from the solid phase to the gas step Deposition: The change from the gas phase to the hard phase


​Fig. 11.1b: four states of matter with transitions in between them.

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Intermolecular forces (IMF)

The the hatchet InterMolecular force (IMF) literally way the forces in between molecules, and as such, is often a misnomer, as just speaking, not all issue is composed of molecules. Yet this term is supplied pervasively, and also so us will usage it, but very first lets compare it to the so dubbed "intramolecular forces", the forces within the proverbial "molecule." We frequently consider two species of bonds, ionic (which are not molecular) and covalent (which are molecular). Therefore if I have liquid water, wherein the discrete reality of issue is the H2O molecule, there are two kind of bonds, those between H and also O of a water molecule (covalent intramolecular) and also those between the H that one molecule and also the O of an additional (intermolecular).

Types that Intermolecular Forces

Ion-Dipole pressures (these might not it is in true IMF, however we will call them IMFs) services Dipole-Dipole pressures (between two polar molecules) Pure problem or services Hydrogen Bonding (special kind of dipole-dipole) Pure problem or options Dipole-Induced Dipole (between polar and nonpolar molecules) options Instantaneous Dipole-Induced Diploe (between two nonpolar molecules, often dubbed London Dispersion Forces) solutions or Pure building materials

Please keep in mind that in recognizing what kind of intermolecular forces are involved we require to understand if a molecule is polar or non-polar. This calls for a testimonial of Lewis period Structures, VSEPR Theory, Electronegativety, and Bond Polarity.

Properties of issue that depend on IMFs

boil point, melting point, stable phases enthalpies of step transitions vapor pressure solubility and also miscibility of various substances viscosity

There are plenty of physical properties of issue that room strongly influenced by IMFs, and also over the next couple of chapters we will look at countless of these. Lets ask a simple question;

Exercise (PageIndex1)

At a given temperature, which would certainly be easier to type a gas, a light molecule or a heavy molecule?


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from our study of gasses and also the Kinetic Molecular concept we learned the the median kinetic energy of a molecular mechanism is proportional to the absolute temperature, and also so both equipment would have the same typical kinetic energy, and we would certainly predict the the lighter molecule would have the greater velocity (review Graham"s legislation of Effusion). Therefore, one would certainly predict (often incorrectly), the it would certainly be easier for the lighter molecule to form a gas than for the more heavier one (and all various other things equal, the lighter molecule would have the lower boiling point). The problem is we need to recognize the intermolecular forces, the will affect the phase change (think carbon dioxide and water - see next question).