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It is likely that every chemistry classroom in the world has a poster of the periodic table of the chemical elements hanging on the wall. Each element enclosed in its own little box, reminding me of the Malvina Reynolds 1960’s song, Little Boxes:

“…There's a pink one and a green one
And a blue one and a yellow one
And they're all made out of ticky-tacky
And they all look just the same”

The ticky-tacky of the elements is nothing less than the fundamental building blocks of everything in the universe that is solid, liquid or gas. Elements are like the letters of the alphabet, the foundational single components of written language. Governed by the rules of spelling, letters combine to make words. Governed by the rules of chemistry, elements combine to make all matter; the planets, oceans, fish, trees, houses, cars and even you and me. Everything around you is made from a 92-letter alphabet of naturally occurring elements.

Elements are defined by the number of protons contained within their atomic nuclei. Hydrogen, for example, has one proton, helium has two protons, all the way to uranium with six protons. Contained within each element however, there is a sub-type known as the isotopes. Along with a defined number of protons, certain atomic nuclei also contain neutrons. Take the element carbon for example. All atomic nuclei of carbon contain six protons but some also have six neutrons, some have seven neutrons and some eight neutrons. Based upon the total number of protons and neutrons in the respective nuclei, the three isotopes of carbon are known as 12C, 13C and 14C. 

A barbecue has carbon in the form of charcoal. If it was possible to separate out the isotopes, then you’d have three piles; 99% would be 12C, 1% would be 13C and about a billionth of one percent would be 14C. Each pile would be indistinguishable. They would look the same, burn in the barbecue the same and be chemically identical.  In fact the chemical properties of carbon isotopes are so similar that in reality it would be impossible to separate them without very sophisticated scientific equipment.  Isotopes are like a language having an alphabet of letters, most of them black but a few of different colours. Letters still combine to make words, it’s just some letters might be black, or red, or blue. 

There are 92 naturally occurring elements but how many isotopes are there? The total is at least four thousand, but it’s a complex question to answer. Some, known as radioisotopes, decay away over time by emitting radioactivity. Some decay at a blink of an eye and some decay slowly over eons. The radioisotope 14C, for example, hangs around for a few thousand years. There are also those known as stable isotopes, such as 12C and 13C, which were born in giant stellar events billions of years ago and will remain unchanged, at least in theory, for ever. 

The isotopes mix and combine, switch and exchange, come and go, like a cosmic dance choreographed at Nature’s decree. The pattern of isotopes in any one place and at any one time leave behind a fingerprint of Nature’s endeavours. Science has aspired to interpret these isotopic fingerprints and in so doing, has opened doors into the natural world. Our knowledge of the age of the Earth relies on isotopes. Much of archeological dating relies on isotopes. Medical research, diagnosis and therapy all rely on isotopes. Past climate, the flow of ocean and river currents, as well as the flow of people across the planet have all left their isotopic fingerprints behind. Isotopes have even told us that the cells in our bodies are not the same as those we were born with. 

The ubiquitous nature of isotopes collectively makes them one of the most useful markers into the scientific world, but few appreciate their utility.  A small minority who hold their own agenda, and perhaps personal prejudice, even misrepresent what the isotopes tell us. I hope this book goes some way to showing the true character of the isotopes and how they have contributed so much to our modern way of life.