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General Chemistry Principles, Patterns, and Applications, 2011

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it only has one O–H bond with an H atom that can act as a hydrogen bond donor. Consequently, methanol<br />

can only form two hydrogen bonds per molecule on average, versus four for water. Hydrogen bonding<br />

therefore has a much greater effect on the boiling point of water.<br />

16.<br />

17.<br />

18.<br />

19.<br />

20.<br />

21. Vigorous boiling causes more water molecule to escape into the vapor phase, but does not affect the<br />

temperature of the liquid. Vigorous boiling requires a higher energy input than does gentle simmering.<br />

[1] There are two additional types of electrostatic interaction that you are already familiar with:<br />

the ion–ion interactions that are responsible for ionic bonding <strong>and</strong> the ion–dipole interactions<br />

that occur when ionic substances dissolve in a polar substance such as water. (For more<br />

information on ionic bonding, see Chapter 8 "Ionic versus Covalent Bonding". For more<br />

information on the dissolution of ionic substances, see Chapter 4 "Reactions in Aqueous<br />

Solution" <strong>and</strong> Chapter 5 "Energy Changes in Chemical Reactions".)<br />

11.3 Unique Properties of Liquids<br />

L E A R N I N G O B JE C T I V E<br />

1. To describe the unique properties of liquids.<br />

Although you have been introduced to some of the interactions that hold molecules together in a liquid, we have not<br />

yet discussed the consequences of those interactions for the bulk properties of liquids. We now turn our attention to<br />

three unique properties of liquids that intimately depend on the nature of intermolecular interactions: surface<br />

tension, capillary action, <strong>and</strong> viscosity.<br />

Surface Tension<br />

We stated in Section 11.1 "The Kinetic Molecular Description of Liquids" that liquids tend to adopt the<br />

shapes of their containers. Why, then, do small amounts of water on a freshly waxed car form raised<br />

droplets instead of a thin, continuous film? The answer lies in a property called surface tension, which<br />

depends on intermolecular forces.<br />

Figure 11.9 "A Representation of Surface Tension in a Liquid" presents a microscopic view of a liquid<br />

droplet. A typical molecule in the interior of the droplet is surrounded by other molecules that exert<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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