poor conductor of electricity. If the electrons in an atom can’t be moved from their orbits at all, the material is an insulator. If at least some of the electrons can be moved, the material is a resistor. Two of the best-known conductors of electricity are silver and copper. The atomic structures of the silver and copper atom are compared in Figure 6. Note that both atoms have only one electron in the outermost orbit. This makes silver and copper excellent conductors of
Silver is actually an even better conductor than copper. Why? Well, even though both silver and copper atoms have free electrons, the free electron in silver is farther away from the nucleus than is the free electron in copper. The farther the free electron is away from the nucleus, the more loosely bound the electron will be to the nucleus. This explains why silver, which has five electron orbits, is a better conductor than copper, which has four orbits. Silver is often used as a coating on electrical conductors in order to keep the resistance as low as possible.
Now, let’s look at an atom of carbon (Figure 7). The nucleus of the carbon atom contains six protons and six neutrons. Six electrons orbit the nucleus. Now, look more closely at the electrons. Note that the electrons orbit the nucleus in two rings, or shells. The inner shell 8 Nature of Electricity
in outermost orbit
Silver atom Copper atom
FIGURE 6—This illustration compares the atomic structures of a silver atom and a copper atom. Both atoms have a free electron in their outermost orbits, and both are good electrical conductors. However, the free electron in the silver atom is farther away from the nucleus than the free electron in the copper atom. This means that the silver electron can more easily be dislodged from its orbit than the copper electron. Thus, silver is an even better electrical conductor than copper.
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