There are over 80 different metals. They tend to conduct heat and electricity well, and many of them can be shaped by pulling, beating, or melting and pouring into a mould. Metals with similar properties are often grouped together, although a metal may sometimes appear in more than one group, as these pages show. Unlike most non-metals, metals are shiny when cut. Metals have played an enormous part in the history of human activity, which is why some periods, such as the Iron Age and the Bronze Age, are known by the names of metals. Some people say that our present period should be called the Silicon Age. But silicon is what is known as a semi-metal, having some but not all of the properties of metals.
Hard, shiny, and tough—metals are the macho poster boys of the material world. Learning how to extract these substances from the Earth and turn them into all kinds of useful materials was one of the most important developments in human civilization, spawning tools, jewelry, engines, machines, and giant static constructions like briges and skyscrapers. Having said that, “metal” is an almost impossibly broad term that takes in everything from lead (a super-heavy metal) and aluminum (a super-light one) to mercury (a metal that’s normally a liquid) and sodium (a metal soft enough to cut like cheese that, fused with chlorine, you can sprinkle on your food—as salt!).
When we talk about nonmetals, it ought to mean everything else—although things are a bit more complex than that. Sometimes you’ll hear people refer to semi–metals or metalloids, which are elements whose physical properties (whether they’re hard and soft, how they carry electricity and heat) and chemical properties (how they behave when they meet other elements in chemical reactions) are somewhere in between those of metals and nonmetals. Semi-metals include such elements as silicon and germanium—semiconductors (materials that conduct electricity only under special conditions) used to make integrated circuits in computer chips and solar cells. Other semi-metals include arsenic, boron, and antimony (all of which have been used in the preparation—”doping”— of semiconductors).
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