The table summarises some typical properties of metals and non-metals.
|High melting points||Low melting points|
|Good conductors of electricity||Poor conductors of electricity|
|Good conductors of heat||Poor conductors of heat|
|High density||Low density|
|Malleable and ductile||Brittle|
Some elements have properties that are not typical. For example:
A substance with a high density means it has a high mass for its size.
Ductile means that a substance can be drawn out into a long wire without snapping or breaking.
Metals and non-metals can also be distinguished by some chemical properties.
The most common chemical property is the type of oxide that the element forms. Metals form oxides that are basic, but non-metals form oxides that are acidic. For example, sulfur and carbon are both non-metals. They react with oxygen to form sulfur dioxide and carbon dioxide. These compounds are both gases present in the air and which dissolve in rain water, making it acidic.
Some oxides do not dissolve in water, so would not affect the colour of an indicator added to the water.
The element thallium forms an oxide, Tl2O. Thallium oxide does not dissolve in water, but does react with acids to form thallium salts. Is thallium a metal or a non-metal? Explain your answer.
Thallium is a metal. This is because thallium oxide reacts with acids, so must be a base. Only metals form oxides that are bases.
Metals are also more likely to corrode than non-metals. This means that non-metals are less likely to react with water or acids than metals are.