Physical properties of metals and non-metals

Metals and non-metals often behave differently when they carry heat or electricity, are shaped, or are heated to high temperatures. These differences are general patterns, not rules that apply to every substance.

Conductivity and shaping

Metals generally conduct heat and electricity well: heat passes through them readily, and electric current can flow through them. Non-metals generally conduct both poorly. There are exceptions; for example, graphite, a form of the non-metal carbon, conducts electricity.

Most metals are malleable, meaning they can be hammered or pressed into shape without breaking. They are also ductile, meaning they can be drawn out into wires. Solid non-metals are generally brittle: when a force is applied, they tend to crack or break rather than bend into a new shape.

Melting and boiling points

A substance’s melting point is the temperature at which it changes from a solid to a liquid. Its boiling point is the temperature at which it boils and changes from a liquid to a gas.

Metals generally have higher melting and boiling points than non-metals. This does not mean that every metal has a higher melting or boiling point than every non-metal.

Reactions of metals with water and steam

Metals differ in how readily they react with water. Some react with cold water, while others react very slowly or not at all with cold water but react with steam. The reaction produces hydrogen gas and a compound of the metal.

Reactions with cold water

Metals that react with cold water generally form a metal hydroxide and hydrogen gas. For example, sodium reacts with water to form sodium hydroxide and hydrogen:

Here, $$\ce{NaOH}$$ is sodium hydroxide and $$\ce{H2}$$ is hydrogen gas.

Reactions with steam

Steam is water in its gaseous state. Some metals that react little or not at all with cold water react with steam instead. They generally form a metal oxide, rather than a hydroxide, and release hydrogen gas.

For example, magnesium reacts very slowly with cold water but reacts with steam to form magnesium oxide and hydrogen:

In this reaction, the $$\ce{H2O}$$ is steam and $$\ce{MgO}$$ is magnesium oxide. The conditions therefore affect both whether a metal reacts and whether the metal compound formed is generally a hydroxide or an oxide.

Reactions of metals with oxygen

When a metal reacts with oxygen, the oxygen combines with the metal to form a metal oxide. The reaction is called oxidation because the metal gains oxygen.

For example, magnesium reacts with oxygen to form magnesium oxide:

Reactivity and oxide formation

Metals differ in how readily they react with oxygen. A more reactive metal generally forms an oxide more easily than a less reactive metal under the same conditions.

Metals can also differ in the rate and extent of the reaction. Rate describes how quickly the oxide forms; extent describes how much of the metal reacts. A metal that reacts slowly may form an oxide over time, while another may react rapidly.