Properties of metal and non-metal elements

Metals are placed on the left-hand side of the periodic table, and non-metals on the right.

Period table with metals in red and non-metals in yellow.

Physical properties

The table summarises some typical properties of metals and non-metals.

MetalsNon-metals
ShinyDull
High melting pointsLow melting points
Good conductors of electricityPoor conductors of electricity
Good conductors of heatPoor conductors of heat
High densityLow density
Malleable and ductileBrittle

Some elements have properties that are not typical. For example:

  • mercury (a metal) has a low melting point and exists as a liquid at room temperature
  • graphite, a form of carbon (a non-metal), has a high boiling point and is also a good conductor of electricity

A substance with a high density means it has a high mass for its size.

Malleable substances can be bent or hammered into shape without shattering, while brittle substances shatter when bent or hit.

Ductile means that a substance can be drawn out into a long wire without snapping or breaking.

Chemical properties

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.

Question

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.