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Chapter 2 Atomic Structure and

Interatomic Bonding

This photograph shows the underside of a gecko.

Geckos, harmless tropical lizards, are extremely fascinating and extraordinary animals. They have

very sticky feet that cling to virtually any surface. This characteristic makes it possible for them to

rapidly run up vertical walls and along the undersides of horizontal surfaces. In fact, a gecko can

support its body mass with a single toe! The secret to this remarkable ability is the presence of an

extremely large number of microscopically small hairs on each of their toe pads. When these hairs

come in contact with a surface, weak forces of attraction (i.e., van der Waals forces) are established

between hair molecules and molecules on the surface. The fact that these hairs are so small and so

numerous explains why the gecko grips surfaces so tightly. To release its grip, the gecko simply curls

up its toes and peels the hairs away from the surface.

Another interesting feature of these toe pads is that they are self-cleaning—that is, dirt particles

don’t stick to them. Scientists are just beginningto understand the mechanism of adhesion for these

tiny hairs, which may lead to the development of synthetic self-cleaning adhesives. Can you image

duct tape that never looses its stickiness, or bandagesthat never leave a sticky residue? (Photograph

courtesy of Professor Kellar Autumn, Lewis & Clark College, Portland, Oregon.)

WHY STUDYAtomic Structure and Interatomic Bonding?

An important reason to have an understanding of

interatomic bonding in solids is that, in some instances,

the type of bond allows us to explain a material’s

properties. For example, consider carbon, which may

exist as both graphite and diamond. Whereas graphite is

relatively soft and has a “greasy” feel to it, diamond is

the hardest known material. This dramatic disparity in

properties is directly attributable to a type of

interatomic bonding found in graphite that does not

exist in diamond (see Section 3.9).

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