The Foundations of Chemistry

218 CHAPTER 5: The Structure of Atoms

E

nrichment

Paramagnetism and Diamagnetism

Substances that contain unpaired electrons are weakly attractedinto magnetic fields and are

said to be paramagnetic.By contrast, those in which all electrons are paired are very weakly

repelled by magnetic fields and are called diamagnetic.The magnetic effect can be measured

by hanging a test tube full of a substance on a balance by a long thread and suspending it

above the gap of an electromagnet (Figure 5-30). When the current is switched on, a para-

magnetic substance such as copper(II) sulfate is pulled into the strong field. The

Iron displays ferromagnetism.

Figure 5-30 Diagram of an apparatus for measuring the paramagnetism of a substance.

The tube contains a measured amount of the substance, often in solution. (a) Before the

magnetic field is turned on, the position and mass of the sample are determined. (b)

When the field is on, a paramagnetic substance is attracted intothe field. (c) A

diamagnetic substance would be repelled very weaklyby the field.

(a) (b) (c)

Sample

Magnet Magnet

No magnetic field

Both paramagnetism and diamagnetism
are hundreds to thousands of times
weaker than ferromagnetism,the effect
seen in iron bar magnets.

(a) (b) (c)