The Generation Game

You already know, if you have read Reaction 6, that an electric current is a stream of electrons. If you have also read the section on redox reactions (Reaction 5), which you should, in preparation for this account, then you will also know that in a redox reaction electrons are transferred from one species to another. Although it is now far too late, had you had that information 150 or so years ago, then you might have realized that if those species were at the opposite ends of a piece of wire, the transfer of electrons would then take place in the form of an electric current travelling along the wire and you would have invented the electric battery. All the batteries that are used to generate electricity and drive portable electrical and electronic equipment, from torches, drills, phones, music players, laptops, through to electric vehicles, are driven by this kind of chemically produced flow of electrons. 

One of the earliest devices for producing a steady electric current was the Daniell cell , which was invented in 1836 by John Daniell (1790-1845) of King s College, London in response to the demand in the nineteenth century of the then emerging technology of telecommunication for a steady, cheap source of electricity. I have already touched on the underlying reaction when 1 explained what happens when a piece of zinc, Zn, is dropped into a solution of copper sulfate (Reaction 5), and this section builds on that account. 

In that reaction copper is deposited on the zinc and the copper sulfate solution gradually loses its colour as blue Cu ions are replaced by colourless Zn ions. As this reaction takes place, electrons hop from the zinc metal onto Cu ions nearby in the solution. If we were to stand there watching, we would see electrons snapping across from the zinc to the Cu ions wherever the latter came within striking distance of the zinc surface. There would be electron transfer, but no net current of electricity. 

Overall, the same reaction has occurred as when zinc is simply dipped into copper sulfate solution, but because the sites of oxidation (Zn to Zn= ) and reduction (Cu to Cu) are now separated spatially, in this arrangement the reaction has generated an electric current. 

Modern portable electronic technology has moved on from earthenware pots (but their descendant ceramics are very much in vogue). Nevertheless, the principles remain the same. In the currently widely used lithium-ion battery, electrons are released from lithium atoms, Li, as they change into Lh ions, and those ions drift away from the electrode. Pure metallic lithium is not used for the electrode in view of a number of difficulties, including the risk of fire. Instead, a range 

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