How Many Ccl4 Molecules of Different Masses Can Exist?

LEARNING OBJECTIVES

By the end of this section, you will exist able to:

• Draw the types of intermolecular forces possible between atoms or molecules in condensed phases (dispersion forces, dipole-dipole attractions, and hydrogen bonding)
• Place the types of intermolecular forces experienced past specific molecules based on their structures
• Explain the relation betwixt the intermolecular forces present within a substance and the temperatures associated with changes in its physical state

As was the case for gaseous substances, the kinetic molecular theory may be used to explicate the behavior of solids and liquids. In the following description, the term particle will exist used to refer to an atom, molecule, or ion. Note that we volition employ the popular phrase "intermolecular attraction" to refer to attractive forces between the particles of a substance, regardless of whether these particles are molecules, atoms, or ions.

Consider these two aspects of the molecular-level environments in solid, liquid, and gaseous matter:

• Particles in a solid are tightly packed together and often arranged in a regular pattern; in a liquid, they are close together with no regular arrangement; in a gas, they are far apart with no regular arrangement.
• Particles in a solid vibrate about fixed positions and do not generally move in relation to i some other; in a liquid, they move past each other but remain in essentially constant contact; in a gas, they move independently of 1 another except when they collide.

The differences in the properties of a solid, liquid, or gas reverberate the strengths of the attractive forces between the atoms, molecules, or ions that brand up each phase. The phase in which a substance exists depends on the relative extents of its intermolecular forces (IMFs) and the kinetic energies (KE) of its molecules. IMFs are the diverse forces of attraction that may exist betwixt the atoms and molecules of a substance due to electrostatic phenomena, every bit will exist detailed in this module. These forces serve to concord particles shut together, whereas the particles' KE provides the energy required to overcome the attractive forces and thus increment the distance betwixt particles. Figure i illustrates how changes in concrete land may be induced by changing the temperature, hence, the average KE, of a given substance.

Effigy ane. Transitions betwixt solid, liquid, and gaseous states of a substance occur when conditions of temperature or pressure favor the associated changes in intermolecular forces. (Note: The space between particles in the gas phase is much greater than shown.)

Effigy 2. Condensation forms when water vapor in the air is cooled enough to form liquid water, such as (a) on the outside of a common cold potable glass or (b) in the class of fog. (credit a: modification of piece of work past Jenny Downing; credit b: modification of work by Cory Zanker)

Figure iii. Butane lighter. (credit: modification of work by "Sam-True cat"/Flickr)

As an case of the processes depicted in this figure, consider a sample of water. When gaseous water is cooled sufficiently, the attractions between H₂O molecules will be capable of holding them together when they come into contact with each other; the gas condenses, forming liquid H₂O. For case, liquid water forms on the outside of a cold drinking glass equally the water vapor in the air is cooled by the cold glass, every bit seen in Figure ii.

Nosotros can too liquefy many gases by compressing them, if the temperature is not as well loftier. The increased pressure level brings the molecules of a gas closer together, such that the attractions between the molecules become strong relative to their KE. Consequently, they form liquids. Butane, C₄H_ten, is the fuel used in disposable lighters and is a gas at standard temperature and pressure. Inside the lighter's fuel compartment, the butane is compressed to a pressure that results in its condensation to the liquid state, every bit shown in Figure iii.

Gaseous butane is compressed within the storage compartment of a disposable lighter, resulting in its condensation to the liquid state.

Finally, if the temperature of a liquid becomes sufficiently depression, or the pressure level on the liquid becomes sufficiently high, the molecules of the liquid no longer have enough KE to overcome the IMF between them, and a solid forms. A more thorough word of these and other changes of state, or phase transitions, is provided in a later module of this chapter.

Access this PhET interactive simulation on states of affair, phase transitions, and intermolecular forces. This simulation is useful for visualizing concepts introduced throughout this chapter.

Forces between Molecules

Nether appropriate weather, the attractions between all gas molecules will crusade them to form liquids or solids. This is due to intermolecular forces, not intramolecular forces. Intramolecular forces are those within the molecule that keep the molecule together, for example, the bonds between the atoms. Intermolecular forces are the attractions between molecules, which determine many of the concrete properties of a substance. Effigy 4 illustrates these different molecular forces. The strengths of these bonny forces vary widely, though usually the IMFs betwixt pocket-size molecules are weak compared to the intramolecular forces that bond atoms together within a molecule. For example, to overcome the IMFs in one mole of liquid HCl and catechumen it into gaseous HCl requires just about 17 kilojoules. Yet, to break the covalent bonds between the hydrogen and chlorine atoms in ane mole of HCl requires nearly 25 times more than energy—430 kilojoules.

Figure four. Intramolecular forces keep a molecule intact. Intermolecular forces concur multiple molecules together and determine many of a substance's backdrop.

All of the bonny forces between neutral atoms and molecules are known as van der Waals forces , although they are usually referred to more informally as intermolecular attraction. We will consider the various types of IMFs in the side by side three sections of this module.

Dispersion Forces

Ane of the 3 van der Waals forces is nowadays in all condensed phases, regardless of the nature of the atoms or molecules composing the substance. This bonny force is called the London dispersion force in honor of German-born American physicist Fritz London who, in 1928, kickoff explained it. This force is frequently referred to as simply the dispersion force . Because the electrons of an atom or molecule are in abiding motility (or, alternatively, the electron'southward location is subject to quantum-mechanical variability), at any moment in time, an atom or molecule can develop a temporary, instantaneous dipole if its electrons are distributed asymmetrically. The presence of this dipole can, in turn, distort the electrons of a neighboring cantlet or molecule, producing an induced dipole . These 2 rapidly fluctuating, temporary dipoles thus result in a relatively weak electrostatic attraction between the species—a so-called dispersion forcefulness like that illustrated in Figure 5.

Figure v. Dispersion forces result from the formation of temporary dipoles, every bit illustrated hither for two nonpolar diatomic molecules.

Dispersion forces that develop between atoms in different molecules can attract the 2 molecules to each other. The forces are relatively weak, however, and become significant just when the molecules are very shut. Larger and heavier atoms and molecules exhibit stronger dispersion forces than do smaller and lighter atoms and molecules. F_ii and Cl_ii are gases at room temperature (reflecting weaker attractive forces); Br₂ is a liquid, and I₂ is a solid (reflecting stronger bonny forces). Trends in observed melting and boiling points for the halogens conspicuously demonstrate this effect, as seen in Table ane.

Table 1. Melting and Boiling Points of the Halogens
Halogen	Molar Mass	Diminutive Radius	Melting Bespeak	Boiling Point
fluorine, F2	38 k/mol	72 pm	53 K	85 K
chlorine, Cl2	71 g/mol	99 pm	172 K	238 K
bromine, Brtwo	160 g/mol	114 pm	266 One thousand	332 M
iodine, I2	254 one thousand/mol	133 pm	387 Chiliad	457 K
astatine, At2	420 g/mol	150 pm	575 K	610 K

The increase in melting and humid points with increasing atomic/molecular size may exist rationalized past because how the strength of dispersion forces is affected past the electronic structure of the atoms or molecules in the substance. In a larger atom, the valence electrons are, on average, farther from the nuclei than in a smaller atom. Thus, they are less tightly held and can more hands form the temporary dipoles that produce the attraction. The measure of how easy or hard it is for another electrostatic charge (for example, a nearby ion or polar molecule) to distort a molecule's accuse distribution (its electron cloud) is known as polarizability . A molecule that has a charge cloud that is easily distorted is said to be very polarizable and volition take big dispersion forces; one with a charge deject that is hard to distort is non very polarizable and volition have modest dispersion forces.

Instance ane

London Forces and Their Furnishings

Society the following compounds of a group 14 element and hydrogen from everyman to highest boiling point: CH_iv, SiH_four, GeH₄, and SnH₄. Explain your reasoning.

Solution

Applying the skills acquired in the chapter on chemic bonding and molecular geometry, all of these compounds are predicted to be nonpolar, so they may experience only dispersion forces: the smaller the molecule, the less polarizable and the weaker the dispersion forces; the larger the molecule, the larger the dispersion forces. The molar masses of CH₄, SiH₄, GeH₄, and SnH₄ are approximately 16 one thousand/mol, 32 k/mol, 77 g/mol, and 123 g/mol, respectively. Therefore, CH₄ is expected to have the everyman boiling indicate and SnH₄ the highest boiling point. The ordering from lowest to highest humid point is expected to exist CH₄ < SiH₄ < GeH₄ < SnH₄.

A graph of the actual boiling points of these compounds versus the period of the Group xiv element shows this prediction to exist correct:

Check Your Learning

Order the post-obit hydrocarbons from lowest to highest humid signal: C₂H₆, C₃H₈, and C_ivH_x.

Answer: C₂H_half-dozen < C₃H_viii < C₄H₁₀. All of these compounds are nonpolar and merely have London dispersion forces: the larger the molecule, the larger the dispersion forces and the higher the humid point. The ordering from lowest to highest boiling signal is therefore C_iiH_six < C₃H_eight < C_ivH_x.

The shapes of molecules also bear on the magnitudes of the dispersion forces between them. For case, humid points for the isomers due north-pentane, isopentane, and neopentane (shown in Figure 6) are 36 °C, 27 °C, and 9.5 °C, respectively. Even though these compounds are composed of molecules with the same chemic formula, C_vH₁₂, the departure in boiling points suggests that dispersion forces in the liquid stage are unlike, beingness greatest for northward-pentane and to the lowest degree for neopentane. The elongated shape of north-pentane provides a greater area available for contact between molecules, resulting in correspondingly stronger dispersion forces. The more compact shape of isopentane offers a smaller surface area available for intermolecular contact and, therefore, weaker dispersion forces. Neopentane molecules are the most compact of the three, offer the least available surface expanse for intermolecular contact and, hence, the weakest dispersion forces. This behavior is analogous to the connections that may be formed between strips of VELCRO brand fasteners: the greater the area of the strip's contact, the stronger the connection.

Figure 6. The strength of the dispersion forces increases with the contact surface area betwixt molecules, as demonstrated past the boiling points of these pentane isomers.

Geckos and Intermolecular Forces

Geckos have an astonishing ability to adhere to well-nigh surfaces. They can quickly sew smooth walls and across ceilings that take no toe-holds, and they do this without having suction cups or a sticky substance on their toes. And while a gecko tin can lift its feet easily as it walks along a surface, if you attempt to selection it upwardly, it sticks to the surface. How are geckos (as well as spiders and some other insects) able to do this? Although this miracle has been investigated for hundreds of years, scientists but recently uncovered the details of the process that allows geckos' feet to behave this way.

Geckos' toes are covered with hundreds of thousands of tiny hairs known as setae, with each seta, in turn, branching into hundreds of tiny, flat, triangular tips called spatulae. The huge numbers of spatulae on its setae provide a gecko, shown in Effigy 7, with a large total area for sticking to a surface. In 2000, Kellar Autumn, who leads a multi-institutional gecko research team, constitute that geckos adhered equally well to both polar silicon dioxide and nonpolar gallium arsenide. This proved that geckos stick to surfaces because of dispersion forces—weak intermolecular attractions arising from temporary, synchronized charge distributions between adjacent molecules. Although dispersion forces are very weak, the total allure over millions of spatulae is large enough to back up many times the gecko'southward weight.

In 2014, ii scientists developed a model to explain how geckos can rapidly transition from "sticky" to "non-gummy." Alex Greaney and Congcong Hu at Oregon Land Academy described how geckos tin can achieve this by changing the angle between their spatulae and the surface. Geckos' feet, which are unremarkably nonsticky, get sticky when a small shear strength is applied. Past curling and uncurling their toes, geckos tin alternate betwixt sticking and unsticking from a surface, and thus easily move beyond it. Further investigations may somewhen lead to the development of meliorate adhesives and other applications.

Figure 7. Geckos' toes contain large numbers of tiny hairs (setae), which co-operative into many triangular tips (spatulae). Geckos adhere to surfaces because of van der Waals attractions between the surface and a gecko's millions of spatulae. By irresolute how the spatulae contact the surface, geckos can plough their stickiness "on" and "off." (credit photograph: modification of work past "JC*+A!"/Flickr)

Picket this video to learn more about Kellar Autumn's research that determined that van der Waals forces are responsible for a gecko'southward power to cling and climb.

Dipole-Dipole Attractions

Think from the chapter on chemic bonding and molecular geometry that polar molecules accept a partial positive charge on one side and a partial negative charge on the other side of the molecule—a separation of charge called a dipole. Consider a polar molecule such equally hydrogen chloride, HCl. In the HCl molecule, the more than electronegative Cl atom bears the partial negative accuse, whereas the less electronegative H atom bears the partial positive charge. An attractive forcefulness betwixt HCl molecules results from the attraction between the positive stop of one HCl molecule and the negative finish of another. This bonny force is called a dipole-dipole allure —the electrostatic force between the partially positive end of one polar molecule and the partially negative stop of some other, every bit illustrated in Figure 8.

Figure 8. This image shows two arrangements of polar molecules, such as HCl, that allow an attraction between the partial negative end of i molecule and the partial positive end of some other.

The effect of a dipole-dipole attraction is credible when we compare the properties of HCl molecules to nonpolar F_ii molecules. Both HCl and F₂ consist of the same number of atoms and have approximately the same molecular mass. At a temperature of 150 Chiliad, molecules of both substances would have the same average KE. Withal, the dipole-dipole attractions between HCl molecules are sufficient to cause them to "stick together" to form a liquid, whereas the relatively weaker dispersion forces betwixt nonpolar F_two molecules are not, and so this substance is gaseous at this temperature. The higher normal humid point of HCl (188 One thousand) compared to F₂ (85 K) is a reflection of the greater strength of dipole-dipole attractions between HCl molecules, compared to the attractions between nonpolar F₂ molecules. We will often apply values such as boiling or freezing points, or enthalpies of vaporization or fusion, every bit indicators of the relative strengths of IMFs of allure present inside different substances.

Case 2

Dipole-Dipole Forces and Their Furnishings

Predict which will have the higher humid betoken: N_ii or CO. Explain your reasoning.

Solution

CO and North₂ are both diatomic molecules with masses of about 28 amu, so they experience similar London dispersion forces. Considering CO is a polar molecule, it experiences dipole-dipole attractions. Because North₂ is nonpolar, its molecules cannot exhibit dipole-dipole attractions. The dipole-dipole attractions betwixt CO molecules are comparably stronger than the dispersion forces between nonpolar Northward_two molecules, then CO is expected to have the higher boiling point.

Check Your Learning

Predict which volition have the higher boiling point: ICl or Br_two. Explain your reasoning.

Answer: ICl. ICl and Br₂ have similar masses (~160 amu) and therefore experience similar London dispersion forces. ICl is polar and thus also exhibits dipole-dipole attractions; Br₂ is nonpolar and does not. The relatively stronger dipole-dipole attractions require more energy to overcome, then ICl volition take the higher boiling point.

Hydrogen Bonding

Nitrosyl fluoride (ONF, molecular mass 49 amu) is a gas at room temperature. Water (H₂O, molecular mass 18 amu) is a liquid, even though it has a lower molecular mass. Nosotros clearly cannot attribute this difference betwixt the two compounds to dispersion forces. Both molecules have almost the same shape and ONF is the heavier and larger molecule. It is, therefore, expected to experience more than pregnant dispersion forces. Additionally, we cannot attribute this difference in boiling points to differences in the dipole moments of the molecules. Both molecules are polar and exhibit comparable dipole moments. The large difference betwixt the boiling points is due to a particularly strong dipole-dipole attraction that may occur when a molecule contains a hydrogen atom bonded to a fluorine, oxygen, or nitrogen cantlet (the three most electronegative elements). The very big difference in electronegativity between the H atom (2.1) and the atom to which information technology is bonded (4.0 for an F cantlet, iii.5 for an O atom, or 3.0 for a North cantlet), combined with the very small size of a H cantlet and the relatively modest sizes of F, O, or Northward atoms, leads to highly full-bodied partial charges with these atoms. Molecules with F-H, O-H, or N-H moieties are very strongly attracted to similar moieties in nearby molecules, a peculiarly potent type of dipole-dipole allure called hydrogen bonding . Examples of hydrogen bonds include HF⋯HF, H_twoO⋯HOH, and H_iiiN⋯HNH₂, in which the hydrogen bonds are denoted by dots. Figure nine illustrates hydrogen bonding between water molecules.

Figure nine. Water molecules participate in multiple hydrogen-bonding interactions with nearby water molecules.

Despite use of the word "bail," keep in mind that hydrogen bonds are intermolecular attractive forces, not intramolecular attractive forces (covalent bonds). Hydrogen bonds are much weaker than covalent bonds, only about 5 to 10% equally potent, but are generally much stronger than other dipole-dipole attractions and dispersion forces.

Hydrogen bonds accept a pronounced effect on the properties of condensed phases (liquids and solids). For example, consider the trends in boiling points for the binary hydrides of group 15 (NH₃, PH₃, AsH₃, and SbH₃), group 16 hydrides (H₂O, H₂S, H₂Se, and H₂Te), and group 17 hydrides (HF, HCl, HBr, and HI). The boiling points of the heaviest three hydrides for each grouping are plotted in Figure 10. As we progress down any of these groups, the polarities of the molecules subtract slightly, whereas the sizes of the molecules increase essentially. The issue of increasingly stronger dispersion forces dominates that of increasingly weaker dipole-dipole attractions, and the boiling points are observed to increase steadily.

Figure 10. For the group 15, 16, and 17 hydrides, the boiling points for each class of compounds increment with increasing molecular mass for elements in periods three, 4, and 5.

If nosotros use this tendency to predict the boiling points for the lightest hydride for each group, we would expect NH₃ to boil at virtually −120 °C, H₂O to boil at about −eighty °C, and HF to boil at about −110 °C. However, when we mensurate the boiling points for these compounds, we find that they are dramatically higher than the trends would predict, as shown in Effigy 11. The stark contrast between our naïve predictions and reality provides compelling evidence for the strength of hydrogen bonding.

Figure 11. In comparison to periods three−5, the binary hydrides of catamenia 2 elements in groups 17, 16 and 15 (F, O and North, respectively) exhibit anomalously high boiling points due to hydrogen bonding.

Example 3

Effect of Hydrogen Bonding on Boiling Points

Consider the compounds dimethylether (CH₃OCH₃), ethanol (CH₃CH_iiOH), and propane (CH_threeCH_twoCH_iii). Their boiling points, not necessarily in order, are −42.1 °C, −24.8 °C, and 78.iv °C. Lucifer each compound with its boiling indicate. Explain your reasoning.

Solution

The VSEPR-predicted shapes of CH₃OCH_iii, CH₃CH₂OH, and CH₃CH₂CH₃ are like, equally are their molar masses (46 g/mol, 46 1000/mol, and 44 g/mol, respectively), so they volition showroom similar dispersion forces. Since CH₃CH₂CH₃ is nonpolar, it may exhibit only dispersion forces. Because CH₃OCH₃ is polar, it volition likewise experience dipole-dipole attractions. Finally, CH_threeCH₂OH has an −OH grouping, and and then it will experience the uniquely potent dipole-dipole allure known as hydrogen bonding. So the ordering in terms of forcefulness of IMFs, and thus humid points, is CH₃CH₂CH₃ < CH₃OCH₃ < CH_threeCH_iiOH. The boiling point of propane is −42.1 °C, the humid point of dimethylether is −24.8 °C, and the humid point of ethanol is 78.5 °C.

Cheque Your Learning

Ethane (CH₃CH_iii) has a melting bespeak of −183 °C and a humid signal of −89 °C. Predict the melting and boiling points for methylamine (CH₃NH₂). Explain your reasoning.

Answer: The melting point and boiling betoken for methylamine are predicted to exist significantly greater than those of ethane. CH₃CH_three and CH₃NH₂ are similar in size and mass, just methylamine possesses an −NH group and therefore may exhibit hydrogen bonding. This greatly increases its IMFs, and therefore its melting and boiling points. It is difficult to predict values, just the known values are a melting signal of −93 °C and a boiling point of −6 °C.

Hydrogen Bonding and DNA

Figure 12. Two split DNA molecules form a double-stranded helix in which the molecules are held together via hydrogen bonding. (credit: modification of piece of work by Jerome Walker, Dennis Myts)

Deoxyribonucleic acid (DNA) is institute in every living organism and contains the genetic information that determines the organism's characteristics, provides the blueprint for making the proteins necessary for life, and serves as a template to pass this information on to the organism's offspring. A DNA molecule consists of ii (anti-)parallel chains of repeating nucleotides, which form its well-known double helical construction, as shown in Figure 12.

Each nucleotide contains a (deoxyribose) carbohydrate bound to a phosphate group on one side, and one of 4 nitrogenous bases on the other. Two of the bases, cytosine (C) and thymine (T), are single-ringed structures known as pyrimidines. The other two, adenine (A) and guanine (Yard), are double-ringed structures chosen purines. These bases class complementary base pairs consisting of one purine and one pyrimidine, with adenine pairing with thymine, and cytosine with guanine. Each base pair is held together by hydrogen bonding. A and T share two hydrogen bonds, C and G share three, and both pairings have a similar shape and structure Effigy 13.

The cumulative effect of millions of hydrogen bonds effectively holds the two strands of DNA together. Importantly, the two strands of DNA tin relatively hands "unzip" down the center since hydrogen bonds are relatively weak compared to the covalent bonds that hold the atoms of the private Deoxyribonucleic acid molecules together. This allows both strands to function as a template for replication.

Figure 13. The geometries of the base molecules result in maximum hydrogen bonding between adenine and thymine (AT) and between guanine and cytosine (GC), so-called "complementary base pairs."

Key Concepts and Summary

The physical properties of condensed matter (liquids and solids) can be explained in terms of the kinetic molecular theory. In a liquid, intermolecular attractive forces hold the molecules in contact, although they all the same have sufficient KE to move by each other.

Intermolecular attractive forces, collectively referred to every bit van der Waals forces, are responsible for the beliefs of liquids and solids and are electrostatic in nature. Dipole-dipole attractions result from the electrostatic attraction of the fractional negative end of 1 dipolar molecule for the partial positive end of another. The temporary dipole that results from the motion of the electrons in an atom can induce a dipole in an side by side cantlet and requite ascent to the London dispersion strength. London forces increment with increasing molecular size. Hydrogen bonds are a special type of dipole-dipole attraction that results when hydrogen is bonded to one of the three most electronegative elements: F, O, or Due north.

Chemical science End of Chapter Exercises

1. In terms of their bulk properties, how exercise liquids and solids differ? How are they similar?
2. In terms of the kinetic molecular theory, in what ways are liquids similar to solids? In what ways are liquids different from solids?
3. In terms of the kinetic molecular theory, in what ways are liquids similar to gases? In what ways are liquids different from gases?
4. Explain why liquids assume the shape of whatever container into which they are poured, whereas solids are rigid and retain their shape.
5. What is the prove that all neutral atoms and molecules exert attractive forces on each other?
6. Open the PhET States of Matter Simulation to respond the following questions:
   1. Select the Solid, Liquid, Gas tab. Explore by selecting dissimilar substances, heating and cooling the systems, and changing the state. What similarities practice you notice betwixt the four substances for each phase (solid, liquid, gas)? What differences do you lot discover?
   2. For each substance, select each of the states and tape the given temperatures. How do the given temperatures for each state correlate with the strengths of their intermolecular attractions? Explain.
   3. Select the Interaction Potential tab, and apply the default neon atoms. Move the Ne atom on the right and observe how the potential energy changes. Select the Full Force button, and move the Ne cantlet as earlier. When is the total force on each atom bonny and large enough to thing? So select the Component Forces button, and move the Ne cantlet. When practise the attractive (van der Waals) and repulsive (electron overlap) forces balance? How does this chronicle to the potential energy versus the distance between atoms graph? Explicate.
7. Ascertain the following and requite an example of each:
   1. dispersion strength
   2. dipole-dipole attraction
   3. hydrogen bail
8. The types of intermolecular forces in a substance are identical whether information technology is a solid, a liquid, or a gas. Why then does a substance change phase from a gas to a liquid or to a solid?
9. Why practise the humid points of the noble gases increase in the order He < Ne < Ar < Kr < Xe?
10. Neon and HF take approximately the same molecular masses.
    1. Explicate why the humid points of Neon and HF differ.
    2. Compare the change in the humid points of Ne, Ar, Kr, and Xe with the alter of the humid points of HF, HCl, HBr, and HI, and explain the deviation betwixt the changes with increasing atomic or molecular mass.
11. Adapt each of the following sets of compounds in society of increasing boiling point temperature:
    1. HCl, H₂O, SiH_iv
    2. F_two, Cl_ii, Br₂
    3. CH₄, C₂H₆, C₃H₈
    4. O_ii, NO, N₂
12. The molecular mass of butanol, C_ivH₉OH, is 74.14; that of ethylene glycol, CH_ii(OH)CH₂OH, is 62.08, still their boiling points are 117.2 °C and 174 °C, respectively. Explain the reason for the departure.
13. On the ground of intermolecular attractions, explain the differences in the boiling points of north–butane (−1 °C) and chloroethane (12 °C), which have similar molar masses.
14. On the basis of dipole moments and/or hydrogen bonding, explicate in a qualitative way the differences in the humid points of acetone (56.two °C) and 1-propanol (97.iv °C), which have similar molar masses.
15. The melting point of H₂O(s) is 0 °C. Would you expect the melting point of H₂South(due south) to be −85 °C, 0 °C, or 185 °C? Explain your answer.
16. Silane (SiH₄), phosphine (PH_three), and hydrogen sulfide (H_iiS) cook at −185 °C, −133 °C, and −85 °C, respectively. What does this advise almost the polar character and intermolecular attractions of the iii compounds?
17. Explain why a hydrogen bond between two water molecules is weaker than a hydrogen bond between ii hydrogen fluoride molecules.
18. Nether certain conditions, molecules of acetic acid, CH₃COOH, form "dimers," pairs of acetic acid molecules held together by strong intermolecular attractions:
    
    Describe a dimer of acetic acid, showing how two CH₃COOH molecules are held together, and stating the type of IMF that is responsible.
19. Proteins are chains of amino acids that can form in a variety of arrangements, one of which is a helix. What kind of IMF is responsible for holding the protein strand in this shape? On the protein image, testify the locations of the IMFs that hold the protein together:
    
20. The density of liquid NH₃ is 0.64 g/mL; the density of gaseous NH_iii at STP is 0.0007 g/mL. Explain the difference between the densities of these two phases.
21. Identify the intermolecular forces present in the following solids:
    1. CH_threeCH_twoOH
    2. CH_iiiCH₂CH_three
    3. CH₃CH₂Cl

Selected Answers

1. Liquids and solids are like in that they are matter composed of atoms, ions, or molecules. They are incompressible and take like densities that are both much larger than those of gases. They are different in that liquids take no fixed shape, and solids are rigid.

3. They are similar in that the atoms or molecules are free to motility from ane position to another. They differ in that the particles of a liquid are bars to the shape of the vessel in which they are placed. In dissimilarity, a gas will expand without limit to fill the space into which it is placed.

five. All atoms and molecules will condense into a liquid or solid in which the attractive forces exceed the kinetic free energy of the molecules, at sufficiently low temperature.

7. (a) Dispersion forces occur as an atom develops a temporary dipole moment when its electrons are distributed asymmetrically about the nucleus. This structure is more than prevalent in large atoms such as argon or radon. A second cantlet can then be distorted by the appearance of the dipole in the outset atom. The electrons of the second cantlet are attracted toward the positive finish of the first atom, which sets upwardly a dipole in the 2nd atom. The net result is apace fluctuating, temporary dipoles that attract ane another (example: Ar).

(b) A dipole-dipole attraction is a strength that results from an electrostatic attraction of the positive terminate of one polar molecule for the negative finish of another polar molecule (instance: ICI molecules attract one another by dipole-dipole interaction).

(c) Hydrogen bonds course whenever a hydrogen atom is bonded to one of the more than electronegative atoms, such as a fluorine, oxygen, nitrogen, or chlorine atom. The electrostatic attraction between the partially positive hydrogen atom in 1 molecule and the partially negative atom in another molecule gives rise to a potent dipole-dipole interaction called a hydrogen bond (case: [latex]\text{HF}\cdots \text{HF}[/latex]. )

9. The London forces typically increase as the number of electrons increment.

11. (a) SiH₄ < HCl < H₂O; (b) F_two < Cl₂ < Br_ii; (c) CH_four < C_iiH₆ < C_threeH₈; (d) N₂ < O_ii < NO

13. Only rather small dipole-dipole interactions from C-H bonds are bachelor to agree n-butane in the liquid country. Chloroethane, however, has rather big dipole interactions because of the Cl-C bond; the interaction is therefore stronger, leading to a higher boiling betoken.

fifteen. −85 °C. Water has stronger hydrogen bonds so information technology melts at a higher temperature.

17. The hydrogen bond between two hydrogen fluoride molecules is stronger than that betwixt two water molecules because the electronegativity of F is greater than that of O. Consequently, the partial negative charge on F is greater than that on O. The hydrogen bond betwixt the partially positive H and the larger partially negative F will exist stronger than that formed between H and O.

19. H-bonding is the principle International monetary fund holding the DNA strands together. The H-bonding is betwixt the [latex]\text{N}-\text{H}[/latex] and [latex]\text{C}=\text{O}[/latex].

21. (a) hydrogen bonding and dispersion forces;

(b) dispersion;

(c) dipole-dipole attraction and dispersion forces

Glossary

dipole-dipole attraction
intermolecular attraction between two permanent dipoles

dispersion force
(also, London dispersion force) attraction between ii speedily fluctuating, temporary dipoles; pregnant only when particles are very shut together

hydrogen bonding
occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three about electronegative elements: F, O, or N

induced dipole
temporary dipole formed when the electrons of an cantlet or molecule are distorted past the instantaneous dipole of a neighboring cantlet or molecule

instantaneous dipole
temporary dipole that occurs for a cursory moment in fourth dimension when the electrons of an atom or molecule are distributed asymmetrically

intermolecular force
noncovalent bonny force between atoms, molecules, and/or ions

polarizability
mensurate of the ability of a charge to distort a molecule'southward charge distribution (electron cloud)

van der Waals force
attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

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Source: https://courses.lumenlearning.com/wsu-sandbox2/chapter/intermolecular-forces/

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