Question

What trends are there in conductivity of molecules across the periodic table and why?

Answer 1

By conductivity, we mean the ability of elements to act as charge carriers. We know that metals easily lose their valence electrons to the conduction band and result in very good conductivity, unlike non-metals, which have higher separation between the valence band and conduction band and results in poor conductivity.

Hence, as a general trend, metals are known to have good conductivity while non-metals show poor conductivity.

We also know that metals are placed to the left of the periodic table and non-metals are placed in the right. Also note that there are semi-metals or metalloids that has intermediate conductivity and are placed in between metals and non-metals in periodic table.

Hence, we can write

"Conductivity decreases as we go from left to right across a period in periodic table as the metallic character decreases."

Now that we have established that conductivity mainly relies on metallic character, we can expand its use to predict conductivity trend in a group. As we go down a group, the ionization energies of the valence electrons decrease significantly, i.e. electrons are easier to remove. Hence, their availability to the conduction band is even more resulting in higher conductivity. Also, the metallic character increases as we go down the group. Hence, we will expect the conductivity to increase down the group.

Hence, we can write

" Conductivity increases as we go from top to bottom down a group in periodic table as the metallic character increases"

Note that for many of the gaseous non-metals the conductivity is almost close to zero.

Also note that there will be many exception to this general trend owing to many different effects.