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T

HE READER MIGHT WONDER WHY an entire chapter is devoted to

surfaces. After all, they seem fairly easy to understand: the physical bound-

ary of any condensed-phase object is called a surface,and there doesn’t seem

to be anything special about them. The top of a desk, the blacktop of a road,

are surfaces that we encounter daily, and there does not seem to be any un-

usual behavior associated with them.

Perhaps on a mundane level this is true. But now that we understand that

matter is composed of atoms, that these atoms behave according to the laws of

thermodynamics and quantum mechanics, and that gas and solid phases them-

selves behave in some understandable fashion, we should be willing to think

that surfaces are worthy of special attention. A surface represents a series of

points making a plane where one material ends and another begins. This dis-

continuity of matter means that the bulk properties of the material will not

necessarily be found at the surface. In order to understand how surface prop-

erties differ from bulk properties, we need to consider some of the ways sur-

faces are defined and how they are different from the bulk material.

Therefore, we conclude our presentation of physical chemistry by considering

surfaces. This topic has been placed at the end of the book because many of

the ideas considered in previous chapters are applied here: thermodynamics,

quantum mechanics, kinetics, and the structure of the solid state. Rather than

consider the physical chemistry of surfaces in different chapters as some texts

do, we present it a single chapter and see how the models of physical chem-

istry can be used to understand the behavior of surfaces.

22.1 Synopsis

Surfaces are everywhere, but (or because of this) they are easily ignored.

However, they have a major impact on our understanding of matter and how

matter interacts.

There are several ways we can consider surfaces. First, we can think of a

surface as a thin film, one atom or molecule thick. Second, we can consider a

surface as an interface between two different materials, like the boundary be-

tween two immiscible liquids or between a liquid and a gas or a vacuum, or a

solid and a gas, a liquid, or a vacuum. Third, we can consider surfaces as

22.1 Synopsis

22.2 Liquids: Surface Tension

22.3 Interface Effects

22.4 Surface Films

22.5 Solid Surfaces

22.6 Coverage and Catalysis

22.7 Summary

Surfaces