Electrical conductivity across period 3
After studying this page, you should be able to:
- describe and explain how electrical conductivity varies across period 3
The table shows electrical conductivity values for the elements Na to Ar, relative to aluminium.
|Element||Symbol||Atomic number||Electrical conductivity|
Substances conduct electricity if they contain charged particles that can move from place to place when a potential difference is applied.
The table give some information about different substances.
Substance Notes metal conduct when solid or liquid covalent substances do not conduct (graphite is an exception) ionic compounds conduct when dissolved or when liquid
Description of trend
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.
|Elements||Type of element||Type of structure||Description|
|Na, Mg, Al||metal||metallic||conductivity increases from Na to Al|
|Si||metalloid||giant covalent||conductivity much less than Na, Mg and Al|
|P, S, Cl, Ar||non-metal||simple molecular
(Ar is monatomic)
|do not conduct electricity|
Explanation of this trend
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.
Silicon has a giant covalent structure. It is a semiconductor, so it is not a good conductor or a good insulator.
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.
Metallic bonding is often incorrectly described as the attraction between positive metal ions and delocalised electrons. However, metals still consist of atoms, but the outer electrons are not associated with any particular atom.
In a similar way, graphite (a non-metal) also has delocalised electrons. However, you don't see the idea that it consists of carbon ions.
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.
The atoms in molecules of phosphorus, sulfur and chlorine are held together by covalent bonds.