What is ionisation?

In order to understand ionisation it helps to understand static electricity.

If you've ever rubbed a balloon on your jumper and then stuck it to the wall, you've experienced ionisation in action!

All matter is made up of tiny, tiny things called atoms. (The word 'atomic' is from Greek and actually means 'indivisible'. When atoms were discovered it was thought that they were the smallest pieces you could divide matter into. This turned out not to be true.) In fact, atoms themselves are made up of even smaller particles: neutrons, protons and electrons.

Protons and electrons have a special property: they carry electric charge. A proton carries a positive charge and an electron carries a negative charge. Electric charges can attract or repel each other in much the same way as a magnet. The rule is: like charges repel, whilst opposites attract.

The centre of every atom has a nucleus made up of protons and (usually) neutrons around which swarm a number of electrons held in orbit by virtue of their electric charge. They are attracted to the protons in the centre. (It's a little bit like the way the planets orbit the sun because they are attracted by gravity.)

An atom always has the same number of electrons as protons and so its overall charge is zero because the negative electrons cancel out the positive protons. Silver atoms for example have 47 protons and 47 electrons.

There are certain events which can add or remove one or more of the orbiting electrons from atoms resulting in an 'ion' which is an atom that is no longer electrically neutral and has an overall electric charge. Silver atoms tend to lose an electron and become positively charged overall. So, ionisation is when atoms either gain or lose electrons and become electrically charged. Because of the charge, the ions interact differently with surrounding matter than when they are just atoms. You can literally feel this in action when you rub a balloon. The atoms in the balloon lose electrons and become charged and it's the charge that causes the balloons to be attracted to the wall.

In the case of silver, positive silver ions interact with something called a disulphide bond in the bacteria changing the shape of the bond and preventing the bacteria from multiplying. Silver ions also help to generate oxygen from the surrounding water or air which destroys the cell walls of bacteria.

Silver atoms will ionise in the presence of water. In AgActive socks for example, the silver in them becomes ionised whenever the wearer sweats and so they are extremely effective at preventing the growth of bacteria responsible for foot odour and killing the fungus that causes Athlete's foot.

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