Conductivity of water and chlorine?

I am a novice in chemistry and i have a question: I know that water is not a good conductive material (since there is a perfect bond in water I think) but I am thinking that if we add chlorine which has 7 valence electrons this means that there is a hole and this increases conductivity... am I right?




In a nutshell, water is very much ***not*** like semiconductors. Its conductivity is due to altogether different mechanism, and follows different trends.


Typical semiconductor is a rigid network of atoms held together with bonds. Nearly any "wrong" atom would provide either extra electrons or holes (that is, missing electrons). Holes and electrons are the [charge carriers](https://en.wikipedia.org/wiki/Charge_carrier) here. Being very small, they move fast, so you only need a tiny amount of those impurity atoms (say, a few ppm) to create significant conductivity.


Water is quite different. You can't have free electrons in water, to begin with; they will instantly react with something and become ions. Ditto for holes. Ions are the only allowed charge carriers in water. Ions are as big as atoms, and each carries a thick coat of water molecules stuck to it, so effectively they are even *bigger* than atoms. An ion would move in an electric field, but with great difficulty, much like a man pushing his way through a busy crowd. (Compared to it, the electrons would be like little sparrows darting overhead.) Therefore you need **a lot** of ions to create some real conductivity.


Things that produce ions in water (*dissociate*, as we say) are called electrolytes, and there is plenty of them around. For example, table salt dissociates into $\ce{Na+}$ and $\ce{Cl-}$; sulphuric acid dissociates into $\ce{H+}$ and $\ce{SO4^2-}$. Elemental chlorine ($\ce{Cl2}$), being a neutral molecule, does not dissociate; also, you can't add much of it, for it is a gas, and its solubility is not that great. Over time, it would react with water to produce certain compounds which **do** dissociate, so you'll have some conductivity after all, but that's a weird and inefficient way of achieving it. Using any soluble salt is much more straightforward.


The choice of particular electrolyte depends on your ultimate purpose.


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