Electrical conductivity across period 3


Learning outcomes

After studying this page, you should be able to:

  • describe and explain how electrical conductivity varies across period 3.

Electrical conductivity

The table shows electrical conductivity values for the elements sodium to argon, relative to aluminium (which I have set at 1).

ElementSymbolAtomic numberElectrical conductivity

Substances conduct electricity if they contain charged particles that can move from place to place when a potential difference is applied.

The table below gives some information about different substances.

Type of substance Notes
Metal Conduct when solid or liquid
Covalent substance Do not conduct (graphite is an exception)
Ionic compound Conduct when dissolved or when liquid


The graph shows how electrical conductivity varies across period 3.

There is a lot going on in this graph, so it is often easier to divide it into three sections. The table below gives a brief summary of these sections.

Element(s)Type of elementType of structureDescription
Na, Mg, AlMetalMetallicConductivity increases from Na to Al
SiMetalloidGiant covalentConductivity much less than Na, Mg and Al
P, S, Cl, ArNon-metalSimple molecular
(Ar is monatomic)
Do not conduct electricity

When you click on the download symbol, you will be able to download the graph as an image file or pdf file, save its data, annotate it, and print it.


Sodium, magnesium and aluminium

Sodium, magnesium and aluminium are all metals. They have metallic bonding, in which the nuclei of metal atoms are attracted to delocalised electrons.

Going from sodium to aluminium:

  • the number of delocalised electrons increases …
  • there are more electrons that can move and carry charge through the structure …
  • the electrical conductivity increases.

Metallic bonding is often described as the attraction between positive metal ions and delocalised electrons. This is incorrect because metals still consist of atoms, but the outer electrons are delocalised and are free to move through the structure.


Silicon has a giant covalent structure. It is a semiconductor, so it is not a good conductor or a good insulator.

The giant lattice structure of silicon is similar to that of diamond. Each silicon atom is covalently bonded to four other silicon atoms in a tetrahedral arrangement.

Phosphorus, sulfur, chlorine and argon

The remaining elements in period 3 do not conduct electricity. They have no free electrons that can move around and carry charge from place to place.

The atoms in molecules of phosphorus, sulfur or chlorine are attracted to each other by covalent bonds.