Metal

A metal is a type of material that is usually shiny, hard, and good at carrying heat and electricity. Most metals come from the ground, inside rocks called ores. Iron, copper, gold, silver, aluminum, and tin are all metals. More than three-quarters of the elements on the periodic table are metals.

Metals share a few key traits. They are shiny when freshly cut or polished. They bend instead of breaking when hit, which means you can hammer them into flat sheets or pull them into long wires. They also let heat and electricity pass through easily. That is why pots are made of metal and electrical wires are made of copper.

Metals have these traits because of how their atoms behave. In most materials, each atom holds tightly to its own electrons. In metals, the atoms share a loose "sea" of electrons that can move around freely. Those moving electrons carry electricity through a wire and carry heat through a pan.

Humans have used metals for thousands of years. The first metal people worked with was probably copper, about 9,000 years ago. Later, people learned to mix copper with tin to make bronze, a harder metal. That discovery was so important that a whole period of history is called the Bronze Age. Around 3,000 years ago, people figured out how to heat iron ore hot enough to shape it. The Iron Age began, and iron tools and weapons spread around the world.

Different metals have different jobs. Iron mixed with a little carbon becomes steel, which is used in cars, bridges, and tall buildings. Aluminum is light, so it is used in airplanes and soda cans. Copper carries electricity well, so it fills the wires inside your walls. Gold does not rust or tarnish, which is why ancient gold treasures still shine after thousands of years.

Not every metal is safe. Mercury and lead can poison people, and scientists once used them without knowing the danger. Old paint sometimes contained lead. Old thermometers held mercury. Today, both are carefully controlled.

Metals are one of the most recycled materials on Earth. A steel can, a copper pipe, or an aluminum foil ball can be melted down and made into something new, again and again, without losing its strength. The steel in a skyscraper today may once have been part of an old car, a bridge, or a washing machine.