Ions

A long time ago, sci­en­tists no­ticed that wa­ter that was free of im­pu­ri­ties did not con­duct an elec­tric cur­rent at all.

But if salt is poured into the wa­ter, the so­lu­tion will be­come a con­duc­tor. Look, the light is on!

But why does an aque­ous so­lu­tion of sodi­um chlo­ride con­duct elec­tric­i­ty?

To an­swer this ques­tion, let's take a small grain of ta­ble salt and look in­side it.

So right now you are as small as an atom and you are fly­ing in­side a crys­tal. You have prob­a­bly al­ready no­ticed that there are par­ti­cles of two kinds here - small­er…… and big­ger ones.

These par­ti­cles look like atoms. But let's take a clos­er look at these par­ti­cles.

We start with one that is small­er in size.

It looks like a nor­mal atom.

It has a nu­cle­us and an elec­tron shell.

And it con­sists of 10 elec­trons……. 12 neu­trons…….. and 11 pro­tons.

So, as it con­tains 11 pro­tons it seems to be a sodi­um atom.

But look, there are only 10 elec­trons in this par­ti­cle!

You might say: Well, what's wrong with that? Let it be ten elec­trons, what's the prob­lem?

Let's try to build a sodi­um atom. Pro­tons and neu­trons form the nu­cle­us.

And as we have 11 pro­tons, so we need 11 elec­trons to form a sodi­um atom. But we have only ten! In our par­ti­cle, there is one elec­tron less than in the sodi­um atom and the par­ti­cle as a whole will have a pos­i­tive charge plus one.

Let's add one more elec­tron.

Now it is a sodi­um atom.

It is much big­ger than our par­ti­cle.

Re­move the elec­tron from the sodi­um atom and look again at our par­ti­cle. Our par­ti­cle is much small­er than the sodi­um atom. And it has a pos­i­tive charge.

We call this par­ti­cle an ion.

And we have a spe­cial sym­bol for this pos­i­tive sodi­um ion: sodi­um plus. But who could take an elec­tron from a sodi­um atom? Let's find this thief.

We go back to our salt crys­tal.

Now let's look care­ful­ly at the big­ger par­ti­cles.

Choose this one, for ex­am­ple.

It also has a nu­cle­us and an elec­tron shell. It con­sists of 18 elec­trons…… 18 neu­trons……. and 17 pro­tons.

So, it seems to be chlo­rine.

But if we build a chlo­rine atom from these par­ti­cles, then one ex­tra elec­tron will re­main.

We at­tach this elec­tron to the chlo­rine atom and get our par­ti­cle.

In this par­ti­cle, there is one elec­tron more than in chlo­rine atom and the par­ti­cle as a whole has a neg­a­tive charge - mi­nus one.

Now we go back to the lab.

Now you know that in­side ta­ble salt we have ions - sodi­um plus and chlo­ride mi­nus.

These ions are at­tract­ed to each oth­er. And to re­turn to our ques­tion - why does the so­lu­tion of sodi­um chlo­ride con­duct an elec­tric cur­rent?

Re­mem­ber: wa­ter con­sists of un­charged par­ti­cles, H2O mol­e­cules, but ta­ble salt con­sists of charged ions.

Charged par­ti­cles help elec­trons pass through the so­lu­tion, so an aque­ous so­lu­tion of salt con­ducts elec­tric­i­ty, but pure wa­ter does not.

What is flu­o­rine mi­nus?

The flu­o­rine atom, which gains an elec­tron, be­comes an ion with a mi­nus one charge.