Chemistry
Ion dipole Forces
Ion-dipole forces are attractive interactions between an ion and a polar molecule. These forces occur when a charged ion is attracted to the partial charges of a polar molecule, leading to the formation of a stable bond. Ion-dipole forces play a significant role in various chemical processes, such as solvation and the dissolution of ionic compounds in polar solvents.
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11 Key excerpts on "Ion dipole Forces"
eBook - PDF- Geoffrey M. Bowers, Ruth A. Bowers(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
Thus, simply by arranging the molecules such that the positive end of one molecular dipole is near the negative end of another, we develop an attractive dipole–dipole interaction in any system of polar molecules. A second important intermolecular force in systems that contain polar molecules is the ion–dipole interaction , in which an ion is attracted to one of the poles on the polar molecule. Recall that dipole moments develop from nonuniform distributions of charge in space. As discussed in the previous paragraph, any molecule with a dipole moment contains a region that has a net partial negative charge and a net partial posi-tive charge. If you have a partially negative region in a molecule and it approaches a positively charged ion, then an electrostatic attraction develops, because unlike charges attract. An analogous line of reason-ing can be used to explain the attraction of a negative ion to the positive region of a polar molecule. Ion–dipole forces can only exist if a system contains both ions and polar molecules, such as the situation in saltwa-ter. Ion–dipole forces are similar in magnitude to dipole–dipole forces and are stronger when the ion has a greater charge, when the ion has a smaller size, when the molecule has a larger dipole moment, or when the molecule has a smaller size. Another very important intermolecular force that is present only in specific situations is hydrogen bonding . Hydrogen bonds are too weak to be considered chemical bonds, but they are much stronger than the other types of intermolecular forces, typically an order of magnitude stronger (e.g., 40 kJ/mol versus 4 kJ/mol for dipole–dipole interactions). Currently, it is accepted that hydrogen bonds form when hydrogen bound to oxygen, fluorine, or nitrogen interacts with lone-pair electrons on another oxygen, fluorine, or nitrogen.
eBook - PDF- Iam Torrens(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
When for example an ion approaches a neutral atom, its effect is to attract the atomic electrons and repel the nucleus, inducing a dipole moment in the atom. The net effect is an attractive force between the now polarized atom and the ion (see Fig. 1.1(a)), which may be calculated quantum mechanically to yield a potential varying as the inverse fourth power of r. If the ion itself is replaced by a point dipole, the variation is with r 6 . In a similar fashion, dispersive forces exist between neutral atoms at large separations because of the interaction between the electron distributions of the two atoms. In order to minimize the electron contribution to the potential energy of the system, any asymmetry in the electron distribution of one of the atoms leading to an instantaneous dipole moment will induce a similarly directed dipole moment in the other (see Fig. 1.1(b)). The interaction between these two dipoles results in an attractive potential varying as r 6 . This is known as the London-van der Waals force. Higher-order dispersive forces due to higher multipole terms also exist and give potentials varying as r~ 2n W = -( * i * 2 / r ) (1.9) r ( 1 . 1 0 ) ( « > 3 ) . 1.5 The Chemical Bond 9 (a) -+ - + Fig. 1.1 As two atomic systems approach each other, the two-body approximation becomes less satisfactory, except in the other extreme of very high-energy collisions where the overwhelming contribution to the force is nuclear. The many-body problem has been solved for such simple systems as He-He, but the accurate quantum mechanical treatment of the interaction between heavier atoms becomes impracticable. Some quite basic approximations in the atomic model are then necessary. As has been pointed out in Section 1.2, the short-range forces arise as a consequence of the Pauli principle. They manifest themselves as either repulsive elastic forces or attractive valence forces.
eBook - PDFChemistry for Today
General, Organic, and Biochemistry
- Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
dipolar force The attractive force that exists between the positive end of one polar molecule and the negative end of another. hydrogen bonding The result of attractive dipolar forces between molecules in which hydrogen atoms are covalently bonded to very electronegative elements (O, N, or F). TABLE 4.9 The Behavior of Selected Pure Substances in Response to Heating Behavior or State of Substance Temperature (°C) Oxygen (O 2 ) Carbon Monoxide (CO) Water (H 2 O) Salt (NaCl) Copper (Cu) Quartz (SiO 2 ) 2220 Solid Solid Solid Solid Solid Solid 2218 Melts Solid Solid Solid Solid Solid 2199 Liquid Melts Solid Solid Solid Solid 2192 Liquid Boils Solid Solid Solid Solid 2183 Boils Gas Solid Solid Solid Solid 0 Gas Gas Melts Solid Solid Solid 100 Gas Gas Boils Solid Solid Solid 801 Gas Gas Gas Melts Solid Solid 1083 Gas Gas Gas Liquid Melts Solid 1413 Gas Gas Gas Boils Liquid Solid 1610 Gas Gas Gas Gas Liquid Melts 2230 Gas Gas Gas Gas Liquid Boils 2595 Gas Gas Gas Gas Boils Gas 2600 Gas Gas Gas Gas Gas Gas Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Forces between Particles 127 Ozone, O 3 , is a gas that occurs both in the Earth’s upper at- mosphere and at ground level. Ozone is an allotrope of oxy- gen. Allotropes are different molecular forms of the same element. Ozone can be good or bad for your health and the environment, depending on its location in the atmosphere. Ozone occurs in two layers of the atmosphere. The layer closest to the Earth’s surface is the troposphere.
eBook - PDFApplications of Environmental Aquatic Chemistry
A Practical Guide, Third Edition
- Eugene R. Weiner(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
On average, however, molecules tend to move away from the repulsive forces and toward the attractive forces. Because the magnitude of electrostatic forces decreases when molecules move farther apart and increases when molecules approach closer, the temporary attractive elec-trostatic forces always dominate over the temporary repulsive forces. Thus, the effect of these transitory dipole moments is to create another net attractive force in addition to the polar and ionic attractions. Even in a substance of only nonpolar molecules, there will be attractive forces that induce phase changes with changing temperature. Attractions between nonpolar molecules are called dispersion forces or London forces (after Professor Fritz London, who gave a theoretical explanation for them in 1928). The magnitude of dispersion force attractions depends on how easily a mole-cule’s electron cloud can be distorted in a collision, a property called polarizability (see Section 2.8.7). The electron cloud of large molecules having many electrons at longer distances from their nuclei is more easily distorted (high polarizability) than the electron cloud of small molecules, where the charge cloud is closer and held more tightly to the nuclei (low polarizability). Thus, the large nonpolar hydrocarbon molecules of wax have strong enough dispersion attractive forces to be solid at room temperature, while the smaller nonpolar molecules of gasoline are liquid and the still smaller nonpolar molecules of methane are gaseous. Hydrogen bonding : An especially strong type of dipole–dipole attraction, called hydrogen bonding, occurs among molecules containing a hydrogen atom cova-lently bonded to a small, highly electronegative atom that contains at least one 55 Chapter 2: Contaminant Behavior in the Environment valence shell nonbonding electron pair.
eBook - PDFFundamentals Of Atomic Force Microscopy - Part I: Foundations
Part I: Foundations
- Ronald G Reifenberger(Author)
- 2015(Publication Date)
- World Scientific(Publisher)
The near-field local electric fields generated by molecular dipoles are often sufficiently strong to remove atoms from compounds with high melting temperatures. As an example, common table salt (NaCl) is known to melt at 1074 K (800 ◦ C) yet it readily dissolves at room temperature in water, a polar solvent having a molecular dipole moment of 1.8 D. Also, the boiling point of common polar solvents is correlated with increasing dipole moment as shown in Fig. 2.11, indicating that dipole– The Force between Molecules 41 dipole inter-molecular interactions play an important role in determining the physical properties of liquids. 2.6 Dipole Moments in External Electric Fields Before ending this review, it is useful to mention a few of the electro-static consequences of a molecule with a permanent dipole moment. First, the electric field that develops around a dipole has interesting properties. Because the dipole has charges of equal but opposite polarity, the electric field far from the dipole will be small but in close proximity to the dipole, the electric fields can be large and highly non-uniform. This is schematically illustrated in Fig. 2.12 by plotting the dipolar electric field that develops when two charges + q , − q are separated by a distance d . The magnitude of the dipole moment is given by | p | ≡ p = | q | d. (2.20) The direction of p is defined from the negative to the positive charge. It is also useful to consider the work required to rotate a dipole, fixed at a point in space but free to rotate about its midpoint when placed in Fig. 2.12 An electric dipole is formed when two equal but opposite charges are displaced and rigidly held apart by a distance d . Such a charge configuration can be characterized by an electric dipole moment of magnitude p = qd . The direction of p points from negative to positive charge. The spatial dependence of the electric field that develops in close proximity to the dipole is schematically plotted.
- Nobuhiko Yui(Author)
- 2002(Publication Date)
- CRC Press(Publisher)
Heterogeneous or wobble distribution of an electron causes instan-taneous dipole formation of nonpolar groups. The instantaneous dipole induces po-larization of adjacent molecules, leading to a very weak dipole/dipole interaction. The London dispersion force is inversely proportional to r 6 , so that it only acts on groups contacting each other. The interaction is, hence, an influential factor deter-mining protein conformations because a number of groups are in contact in folded protein structures. Similarly, assembling and recognition of macromolecules largely rely on the London dispersion forces. The interactions between uncharged molecules such as dipole/dipole, dipole/induced dipole, and London dispersion forces construct the van der Waals interaction between molecules. FIGURE 4.2 Macrodipole generation on a helical peptide. Electrostatic Interaction 69 4.3 COUNTERION CONDENSATION ON POLYIONS Polyions (or polyelectrolytes) that have multivalent ionic groups along their polymer chains show inherent characteristics different from noncharged or low charged poly-mers. Polyions are classified into three categories: polycations, polyanions, and polyampholytes. Polyampholytes are ionic polymers having both positive and nega-tively charged groups, whereas polycations and polyanions have positively and neg-atively charged groups, respectively. Polycations and polyanions have extended chain conformations owing to repulsive forces among homologously charged groups; polyampholytes have compact conformations due to attractive forces be-tween the opposite charges. High charge density is another intrinsic characteristic of polyions. The high density of charged groups along the backbones of polyions (poly-cations or polyanions) attracts many counterions to its immediate neighborhood (counterion condensation).
eBook - ePubSome Electrical and Optical Aspects of Molecular Behaviour
The Commonwealth and International Library: Chemistry Division
- Mansel Davies, Robert Robinson, H. M. N. H. Irving, L. A. K. Staveley(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
However, the dipole formed (α E) will necessarily be oriented along the molecule-ion line in the most favourable way for mutual attraction, i.e. reduction of energy: the energy between the ion and the dipole after it is formed is −μEcosθ = −μE = −αE 2. Thus the net interaction energy for the whole process of bringing the ion from a large (infinite) distance to a distance r from the molecule is Dipole-Induced Dipole Using the last expression, it is possible to find the net interaction between a dipole and a polarizable molecule—the former inducing a small moment in the latter. If the two molecules, distance r apart, are of polarizabilities α 1 and α 2 and they each have permanent moments μ 1 and μ 2, then the resultant interaction energy when each molecule rotates freely (gaseous state) is found to be Dispersion (or London) Energy All the foregoing attractive energies are of an electrostatic character well understood in non-quantum physics. They also all involve at least one polar feature (ion or dipole) in the pair of molecules. Accordingly, they would not provide attractive forces between non-polar molecules such as the inert gas atoms. The same absence of attraction would be imposed by classical physics on other non-polar compounds such as CH 4, CC1 4, etc., except in so far as, at very close distances of approach, the component dipoles balanced in these structures, e.g. μ (C—Cl), would be found to exert their individual attractive forces. Such molecules, however, readily condense to liquids and solids as a result of attractive forces between them. These forces are again due to molecular polarizability and to the further condition that, at any one instant, the electron cloud of an inert gas atom or of a non-polar molecule is not likely to be strictly spherically symmetrical
eBook - PDFElectrochemistry
A Guide for Newcomers
- Helmut Baumgärtel(Author)
- 2019(Publication Date)
- De Gruyter(Publisher)
2.3 Electrolytes – ions in solution 47 Due to the attracting and repelling electrostatic forces, a short-range order is devel-oped. Every ion is simultaneously central ion and component of the ion cloud around a neighboring ion. The solvent molecules and ions are subject to the ther-mal motion, which counteracts the formation of the near-order. The energy and therefore the chemical potential of the central ion is lowered by its favorable electrostatic interaction with its ionic atmosphere. The main task is to find a way of formulating this effect quantitatively. The Coulomb attraction is taken to be small in comparison to the thermal energy of motion. This assumption is justified for diluted solutions. The average distance of ions in such solutions is large, so that the electrostatic interaction which decreases with the square of the distance is reasonably low. In this diluted solutions, the per-mittivity ε of the solutions is practically identical with that of the solvent. If an outer electric field is applied to the solution the ions start migration. Due to their different charge, the ions move in opposite directions to the electrodes. This leads to two additional effects: the relaxation effect and the electrophoretic effect . The origin of the relaxation effect is the opposite acceleration of the central ion and the ions in the ion cloud. This leads to a partial destruction of the ion cloud, and the rearrangement of the ion cloud needs some time. Therefore, the ion mi-grates ahead of the center of the ion cloud. This leads to a return pointing force slowing down the movement of the ions. The opposite movement of the central ion and the surrounding ion cloud inten-sifies the effect of friction in the solvent. This is called the electrophoretic effect. The basic equations used in the Debye – Hückel theory are the Poisson equation (see Box 4) and the “ Boltzmann distribution.
eBook - ePubSelf-Assembly Processes at Interfaces
Multiscale Phenomena
- Vincent Ball(Author)
- 2018(Publication Date)
- Academic Press(Publisher)
− 6, i.e., very fast.A charged molecule creates an electric field that will deform the electronic cloud of neutral and nonpolar molecules. The electric field then induces an asymmetry in the charge distribution and these molecules, originally nonpolar, acquire an induced dipole. The strength of this dipole depends on the electric field felt by the test molecule and on its intrinsic ability to respond to this field, namely its polarizability, α .The corresponding potential energy of this charge-induced dipole interaction is given byμ induced= α ·E external(2.23)E=p , charge − induced dipole−Q 2· α2 ··(24 π)ε 0D 4(2.24)In the same manner, a permanent dipole creates an electric field in its surroundings inducing a polarization on uncharged molecules and nonpolar molecules but characterized by a polarizability α . The corresponding potential energy is given byE=p , dipole − induced dipole=−μ 2· α·(24 π)ε 0D 6−C inductionD 6(2.25)Finally, it is well known that all neutral and nonpolar molecules and even atoms from rare gazes can form condensed phases at sufficiently low temperatures. Kamerlingh Onnes demonstrated in 1908 that even He can be liquefied. This means that even nonpolar molecules and atoms attract each other when sufficiently close. Even if such entities are nonpolar on average , they display instantaneous dipole moments
eBook - PDF- Donald Voet, Judith G. Voet(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
This arrangement greatly attenuates the coulombic forces be- tween ions, which is why polar solvents have such high di- electric constants. The orienting effect of ionic charges on dipolar mole- cules is opposed by thermal motions, which continually tend to randomly reorient all molecules. The dipoles in a solvated complex are therefore only partially oriented. The reason why the dielectric constant of water is so much greater than that of other liquids with comparable dipole moments is that liquid water’s hydrogen bonded structure permits it to form oriented structures that resist thermal randomization, thereby more effectively distributing ionic charges. Indeed, ice under high pressure has a measured dielectric constant of 3 because its water molecules cannot reorient in response to an external electric field. The bond dipoles of uncharged polar molecules make them soluble in aqueous solutions for the same reasons that ionic substances are water soluble. The solubilities of polar and ionic substances are enhanced if they carry func- tional groups, such as hydroxyl ( ), keto , carboxyl ( or ), or amino ( ) groups, that can form hydrogen bonds with water, as is il- lustrated in Fig. 2-6. Indeed, water-soluble biomolecules such as proteins, nucleic acids, and carbohydrates bristle with just such groups. Nonpolar substances, in contrast, lack both hydrogen bonding donor and acceptor groups. a. Amphiphiles Form Micelles and Bilayers Most biological molecules have both polar (or ionically charged) and nonpolar segments and are therefore simulta- neously hydrophilic and hydrophobic. Such molecules, for ¬NH 2 ¬COOH ¬CO 2 H ( ¬C“O) ¬OH Section 2-1.
eBook - PDF- George C. King(Author)
- 2023(Publication Date)
- Wiley(Publisher)
Although relatively weak, van der Waals forces play a dominant role in the bonding of a wide variety of atomic and molecular systems including, for example, organic molecules, colloidal systems, and pharmaceu- tical drugs. And, interestingly, it is thought that it is the van der Waals force that enables geckos to stick to smooth surfaces such as glass. We also saw, in Section 1.2, that atomic force microscopy exploits van der Waals forces between a surface and the AFM tip to image the surface. 2.3.4 Ionic bonding In the case of van der Waals bonding, we saw that the electric dipole field of an atom distorts the charge distribution of a neighbouring atom. And this results in an attraction between the two atoms. By contrast, in ionic bonding, it is the transfer of an electron from one atom to another that produces the attraction. Consider the example of sodium chloride, (NaCl). An atom of sodium has a total of 11 electrons with the electron configuration 1s 2 2s 2 2p 6 3s. It has one electron, the 3s electron, outside the closed-shell config- uration of neon: 1s 2 2s 2 2p 6 . On the other hand, a chlorine atom has a total of 17 electrons and the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 5 , which means that it is short of one electron compared to the closed-shell con- figuration of argon, which has a complete 3p 6 shell. We recall from Section 1.3.4 that electronic configura- tions having full shells of electrons are particularly stable. Hence, by transferring an electron from a sodium atom to a chlorine atom, we obtain a combination of two particularly stable configurations. This results in a positively charged sodium ion, Na + and a negatively charged chlorine ion, Cl . These attract each other through the Coulomb force and form the molecule NaCl. The potential energy between the sodium ion and the chlorine ion can be written as V r A r p B r 6 e 2 4πε 0 r , (2.14) The forces that bind atoms together 55 where A and B are constants and p has a value close to 9.
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