Conductors, insulators and semiconductors
Electronics has changed everyday life: mobile phones, computers, televisions and radios are all electronic devices.
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Conductors
Conduct electricity: metals (copper, aluminium, iron, lead) and alloys (brass, nichrome, manganin).
The outer electrons of metal atoms are not tightly bound to the nucleus and move about freely.
Insulators
Do not conduct: ebonite, polythene, plastic, dry wood, asbestos, glass.
Strong covalent bonds leave very few electrons free to move.
Semiconductors
Some materials conduct a little electricity: they are semiconductors. Crystalline silicon (Si) and germanium (Ge) are examples. They are in group IV of the periodic table, with four electrons in the outer shell, and form a crystal in which each atom shares electrons with four neighbours to make eight, in stable covalent bonds.
These bonds are weaker than in other insulators, so even the heat available at room temperature breaks some of them and frees electrons.