Periodicity - Electrical Conducitiy Trend

Across the period, there is a change in the electrical conductivity of the elements. Clearly, Na, Mg and Al are metals and hence are good conductors of electricity. While, P₄, S₈, Cl₂ and Ar are simple discrete molecules; the absence of mobile charge particles prevent them from conducting electricity. Lastly, Si as we commonly know is a semi-conductor.

The diagram below depicts the electricial conductivity across Period 3.

Electricial conductivity trend.

In order for us to explain the trend, we need to know the structure the substance exists as. If the substance is a metal, it will have a sea of delocalised electrons available which acts as mobile charge carriers for electricity to be conducted. Thus, simplistically more available the sea of electrons, the better the conductivity. Therefore, structure provides important information to whether there are any charge particles which can move easily.

Flowchart to explaining the conductivity trend.

Interestingly, the explanation to why Si acts as a semi-conductor can be found here. But it is not part of the "A" level syllabus. If you can appreciate the article, you may wish to think about what is the more accurate representation of metallic bonds.

Lastly, there is a slight anonamlly. In this post, I accounted that Al has a higher electrical conductivity as it has a greater pool of delocalised electrons as Al has more valence electrons - Ironically, this contradicts the reasoning to why Al's melting point is not much higher than Mg. However, the details of this reasoning is beyond the scope of this discussion.
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Article written by Kwok YL 2009.}

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