Nonpolar carbon tetrachloride molecules

Polar molecular substances are also soluble in polar water molecules. When a molecular substance such as ethyl alcohol (C2H5OH) dissolves in water (H20), polar ethyl alcohol molecules bond with polar water molecules. In general, likes dissolve likes. Polar solutes will dissolve in polar solvents. In addition, nonpolar solutes dissolve in nonpolar solvents. Nonpolar octane (C8H18) dissolves in nonpolar carbon tetrachloride (CC14). It follows that solutes and solvents of opposite polarity do not form solutions. Nonpolar oil does not dissolve in polar water. (Polar means bearing a charge.)... 

Figure 3.10 shows the vapor pressure/composition curve at a given temperature for an ideal solution. The three dotted straight lines represent the partial pressures of each constituent volatile liquid and the total vapor pressure. This linear relationship is derived from the mixture of two similar liquids (e.g., propane and isobutane). However, a dissimilar binary mixture will deviate from ideal behavior because the vaporization of the molecules A from the mixture is highly dependent on the interaction between the molecules A with the molecules B. If the attraction between the molecules A and B is much less than the attraction among the molecules A with each other, the A molecules will readily escape from the mixture of A and B. This results in a higher partial vapor pressure of A than expected from Raoult s law, and such a system is known to exhibit positive deviation from ideal behavior, as shown in Figure 3.10. When one constituent (i.e., A) of a binary mixture shows positive deviation from the ideal law, the other constituent must exhibit the same behavior and the whole system exhibits positive deviation from Raoult s law. If the two components of a binary mixture are extremely different [i.e., A is a polar compound (ethanol) and B is a nonpolar compound (n-hexane)], the positive deviations from ideal behavior are great. On the other hand, if the two liquids are both nonpolar (carbon tetrachloride/n-hexane), a smaller positive deviation is expected.

FIGURE 5.14 Solubilities, (a) Polar water, with a bit of nonpolar iodine (l ) dissolved in it, floats on top of nonpolar carbon tetrachloride (CCI ), with which it is immiscible, (b) Nonpolar iodine is much more soluble in nonpolar carbon tetrachloride than in water. Therefore, shaking the mixture in (a) causes the iodine molecules to migrate into the carbon tetrachloride, where they produce a purple color. 

A stream of nonpolar carbon tetrachloride (CCI4) molecules is not affected by a charged balloon. 

Is the carbon tetrachloride molecule, CCl4, which contains four polar bonds (electronegativity difference 0.5) polar or nonpolar Explain. 

CCI4. Carbon tetrachloride molecules are nonpolar. Based on the electronegativity difference between Cl and C, we expect a bond dipole for the C—Cl bond. The fact that the resultant dipole moment is zero means that the bond dipoles must be oriented in such a way that they cancel. The tetrahedral molecular geometry of CCI4 provides the symmetrical distribution of bond dipoles that leads to this cancellation, as shown in Figure 10-16(a). Can you see that the molecule will be polar if one of the Cl atoms is replaced by an atom with a different electronegativity, say H In the molecule, CHCI3, there is a resultant dipole moment (Fig. 10-16b). 

Nonpolar molecules such as H, N, O, I, and Cl have zero dipole moments, because e = 0. On the other hand, hydrogen fluoride, HF, has a large dipole moment of 1.75 Debye and so is strongly polar. Simple carbon compounds with symmetric arrangement of like atoms (e.g., methane, CH, and carbon tetrachloride,CCl.,) have zero dipole moments and so are nonpolar. 

Carbon tetrachloride, CCU, is another molecule that, like BeF is nonpolar despite the presence of polar bonds. Each of its four bonds is a dipole, C - — CL However because the four bonds are arranged symmetrically around the carbon atom, they canceL As a result, the molecule has no net dipole it is nonpolar. If one of the Cl atoms in CCI4 is replaced by hydrogen, the situation changes. In the CHCl3 molecule, the H - — C dipole does not cancel with the three C -)— Cl dipoles. Hence CHC13 is polar. 

If the four atoms attached to the central atom in a tetrahedral molecule are the same, as in tetrachloromethane (carbon tetrachloride), CCI4 (30), the dipole moments cancel and the molecule is nonpolar. However, if one or more of the atoms are replaced by different atoms, as in trichloromethane (chloroform), Cl ICI, or by lone pairs, as in NH3, then the dipole moments associated with the bonds are not all the same, so they do not cancel. Thus, the CHCI, molecule is polar (31). 

At the opposite extreme, molecular solids contain individual molecules bound together by various combinations of dispersion forces, dipole forces, and hydrogen bonds. Conforming to like dissolves like, molecular solids dissolve readily in solvents with similar types of intermolecular forces. Nonpolar I2, for instance, is soluble in nonpolar liquids such as carbon tetrachloride (CCI4). Many organic compounds are molecular solids that dissolve in organic liquids such as cyclohexane and acetone. 

The best solvent for a molecular solid Is one whose Intermolecular forces match the forces holding the molecules in the crystal. For a solid held together by dispersion forces, good solvents are nonpolar liquids such as carbon tetrachloride (CCI4) and cyclohexane (Cg H12) For polar solids, a polar solvent such as acetone works well. Example provides some practice in recognizing solubility types. 

Because chlorine is more electronegative than carbon, carbon tetrachloride has four polar covalent bonds. But, as pointed out earlier, the molecular symmetry cancels out the electric dipoles of the individual bonds. The result is a nonpolar molecule. Like water, carbon tetrachloride is a good solvent. At one time, it was used as a dry cleaning agent. Water and carbon tetrachloride, however, dissolve entirely different classes of compounds. Carbon tetrachloride forms solutions with nonpolar organic compounds. It is infinitely miscible, for example, with benzene, whereas water and benzene do not mix. 

You can rule out choice B, hydrogen peroxide, and choice C, water, because the very strong hydrogen bonds between their molecules lower the vapor pressure (the ease at which the liquid evaporates). Although answer A, carbon tetrachloride, the only nonpolar molecule in the list, has only dispersion forces present between molecules, choice D, dichloromethane, has the lowest molecular weight and consequently the lowest amount of dispersion forces. 

Polarity is the extent to which a substance, at molecular level, is characterized by a non-symmetrical distribution of electron density. Polarity is often expressed as dipole moment, which is a function of the magnitude of the partial charges on the molecule, and the distance between the charges. Substances that have larger dipole moments have greater polarity than substances with lower dipole moments. Water and acetone, for example, have dipole moments of 1.85 and 2.80, respectively. Benzene and carbon tetrachloride are nonpolar and have dipole moments of zero. 

In nonpolar molecules such as carbon tetrachloride, the principal attractive force is the London dispersion force, one of the van der Waals forces (Figure 2-24). The London force arises from temporary dipole moments that are induced in a molecule by other nearby molecules. Even though carbon tetrachloride has no permanent dipole moment, the electrons are not always evenly distributed. A small temporary dipole moment is induced when one molecule approaches another molecule in which the electrons are slightly displaced from a symmetrical arrangement. The electrons in the approaching molecule are displaced slightly so that an attractive dipole-dipole interaction results. 

In these two cases the dipole arrows cancel each other out because of the shape of the molecules. The linear shape of the molecule of carbon dioxide puts the dipole arrows in opposite directions to counterbalance each other. The same holds true for the tetrahedral molecular geometry found in carbon tetrachloride. Despite having polar bonds, these two molecules are nonpolar. There is no overall dipole moment in these molecules because the dipole arrows are of the same magnitude but lie in opposite directions in the molecule. This counterbalance causes the molecule to be nonpolar. 

F, T The bonds in carbon tetrachloride are polar but because the molecule is symmetrical, the resulting molecules will be nonpolar. 

Carbon tetrachloride, CCI4, is nonpolar. What forces hold the molecules together ... 

D is correct. Remember that like dissolves like. Water is polar, and will dissolve polar and ionic substances. A, B, C are ions, ionic compounds, or capable of hydrogen bonding. Carbon tetrachloride is a nonpolar molecule. 

These are the London dispersion forces of attraction, or London forces, proposed in 1928 by Fritz London. Every atom, ion, or molecule can engage in London forces, as long as it has at least one electron. London forces are the only intermolecular forces possible in nonpolar substances. London forces are significant only when molecules are veiy close together, essentially touching. They are the forces that are responsible for carbon tetrachloride being a liquid at room temperature. The magnitude of London forces increases as the molecular masses of molecules increase. 

Molecular solids are composed of molecules or atoms. If the molecules are nonpolar, they are held together with London forces forming crystals that are usually soft and melt at lower temperatures. Examples are solid carbon tetrachloride, CCl4fo) (—23°C), and the solid benzene,... 

Nonpolar species Molecules that do not have a permanent dipole and do not have the ability to engage in hydrogen bonding. Many covalent, organic liquids fall into this category oils, solvents derived from petroleum, carbon tetrachloride (CC14), and so on. 

Polar and ionic compounds are more likely to dissolve in a polar solvent, like HzO, than in a nonpolar solvent like CC14 or oil. Polar water molecules are not soluble in oil or carbon tetrachloride, both of which are nonpolar liquids. However, nonpolar compounds, like oils, are soluble in nonpolar solvents but are not soluble in polar solvents like water. The likelihood of forming a solution using solvents and solutes of differing polarity is summarized in the following table. Keep in mind that polar/ionic-nonpolar comparisons have some limitations. Not all ionic compounds are soluble in water, but those that are do not dissolve in nonpolar solvents. 

Hydration, discussed in Section 4.1, is one example of ion-dipole interaction. In an aqueous NaCl solution, the Na and CP ions are surrounded by water molecules, which have a large dipole moment (1.87 D). When an ionic compound like NaCl dissolves, the water molecules act as an electrical insulator to keep the ions apart. On the other hand, carbon tetrachloride (CCI4), a nonpolar molecule, lacks the ability to participate in ion-dipole interaction. Therefore, carbon tetrachloride is a poor solvent for ionic compounds, as are most nonpolar liquids. 

---