Properties of metals

The structure and bonding of metals explains their properties:

  • They are electrical conductors because their delocalised electrons carry electrical charge through the metal.
  • They are good conductors of thermal energy because their delocalised electrons transfer energy.
  • They have high melting points and boiling points, because the metallic bonding in the giant structure of a metal is very strong - large amounts of energy are needed to overcome the metallic bonds in melting and boiling.
  • They are malleable, which means they can be bent and shaped easily. In pure metals, the atoms are arranged in neat layers, and when a force is applied to the metal (eg by being hit with a hammer), the layers of metal atoms can slide over each other, giving the metal a new shape.
Question

Explain why metals can conduct electricity.

Metals conduct electricity because they have delocalised electrons. These carry electrical charge through the metal.

Alloys

An alloy is a mixture of two or more elements, where at least one element is a metal. Many alloys are mixtures of two or more metals.

Comparing properties of alloys and pure metals

Many pure metals are too soft for many uses. They can be made harder by adding another element to the pure metal, so forming an alloy. This explains why an alloy often has more uses than the pure elements it is made from.

Pure iron, for example, is very soft. Adding a small amount of tungsten to iron makes tool steel, which is harder than pure iron. Steels are examples of alloys. There are many types of steel.

SteelElementsProperties
Mild steelCarbon and ironEasy to bend and pull into wires
Tool steelTungsten and ironHard, can be heated to high temperatures
Stainless steelChromium and ironHard, does not rust easily

Explaining alloy hardness

In the solid state, a pure metal has a giant metallic structure. The atoms are arranged in layers. When a force is applied, the layers may slide over each other. The harder and stronger the metal, the greater the force is needed to change or bend it.

In the solid state, a pure metal has a giant metallic structure, the atoms are arranged in layers. When a force is applied, the layers slide over each other.

In a pure metal, the force needed to make the layers slide over each other is small. This explains why many pure metals are soft.

In an alloy, there are atoms of different sizes. The smaller or bigger atoms distort the layers of atoms in the pure metal. This means that a greater force is required for the layers to slide over each other. The alloy is harder and stronger than the pure metal.

Atoms of two different sizes packed together to form an irregular arrangement.Alloys contain atoms of different sizes, making it harder for layers of atoms to slide over each other
Question

Explain why steel, which is an alloy of iron, is harder than pure iron.

Steel contains atoms of other elements as well as iron. These atoms have different sizes to iron atoms, so they distort the layers of atoms in the pure iron. This means that a greater force is required for the layers to slide over each other in steel, so steel is harder than pure iron.

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