The material properties of metals

This nail is hard… But it can also bend… without breaking. This property – being able to change shape without cracking, is called malleability. There are many materials that can bend without cracking. Rubber for instance, and most types of plastic. However, with rubber and plastic, a small force is enough to make them change shape.

They are soft materials. Other materials, such as glass or concrete, can withstand large forces without yielding. They are hard, just like the nail. When the force gets too large these objects don’t bend, but break. These materials are hard, but brittle.

In most cases, the harder a material is, the more brittle it is. And the more malleable a material is, the softer it is. In order to make a nail however, we need a material that can be both hard and malleable. We need a metal. This nail is made of the metal iron.

Iron is an element. This means that in pure iron there are atoms of only one kind – iron atoms. About 60 different kinds of metal atoms can be found in the ground. Together, they account for a quarter of the weight of the Earth’s crust. Some metals are abundant, like aluminium and iron.

Others are rare, like gold. We know of an additional 30 metallic elements, but these don’t occur naturally on Earth. They can only be created artificially, in nuclear reactions. Metals can have very different properties. Some are light; others are heavy.

Some can be heated to thousands of degrees without melting, while one metal is liquid at room temperature. Hardness can also vary a lot between different metals. There are metals that are so soft that you can cut them with a kitchen knife. A few of the metals are brittle. Most metals, however, are both hard and malleable.

We can vary the properties of metals even more, by combining them with each other, or with other substances. The resulting mixtures are called alloys. In this alloy, we have combined two soft metals, forming a hard alloy. So alloys can have different properties from the component elements. And sometimes a metal can become more malleable, even though alloyed with a brittle material.

This makes metals a very versatile group of materials. When we want to make something out of metal, we can use a pure metal - or an alloy - with just the right properties. And we don’t have to choose between a metal that is hard or a metal that is malleable. Because metals can be both – at the same time.