From the rarest metal, to the planet beneath our feet, everything around us is made up of elements. John Emsley, Science Writer in Residence at Cambridge University's Department of Chemistry, will be exploring some of these elements in his National Science Week talk, Elements of Surprise which will take place today (20 March 2002) at 7pm in the Lady Mitchell Hall.

Over 100 different elements have now been discovered. Some are extremely abundant, such as nitrogen, which makes up nearly 80 per cent of the air we breathe; others, such as americium, are very rare but can turn up in unusual places.

"All of the elements we know still fit into a chart called the periodic table," explained Dr Emsley. "The first successful periodic table was drawn up by a Russian, named Dimitri Mendeleyev in 1869. His achievement is remarkable because it was well in advance of its time and he recognised that there were gaps that would be filled as more elements were discovered. Now the table is almost twice as large as the one he devised, and it continues to grow."

Today we know of 113 elements. We encounter many of them in our everyday lives, but some of the rarer elements can turn up where you least expect them. Americium, for example, is a radioactive element, that is most often found in nuclear facilities. But it is also widely used in smoke detectors in the form of americium oxide.

Dr Emsley explains: "The radiation it emits ionizes the air in a gap between two electrodes. When smoke gets in between the electrodes, the current falls, causing an alarm to go off. It's perfectly safe and this is one example of where a radioactive substance can save lives."

Many elements develop surprising properties when they are mixed together to form compounds. Nickel and titanium form an alloy called nitinol, which has the ability to 'remember' a previous shape that it had. This alloy has proved very useful in making spectacle frames that can be bent and twisted, but will jump back to their original shape when released.

And there are the 25 chemical elements that make up the human body, some of which may be highly toxic but if they are lacking in our diet this can seriously affect our health.

Right at the end of the alphabetical spectrum of elements is zirconium, a hard silvery metal. Zirconium oxide, or zirconia, is often used to make fake gems and a particularly famous example of this will be on display at the end of the lecture.

Dr Emsley's talk will take place at 7pm, on 20 March 2002, at the Lady Mitchell Hall, in Sidgwick Avenue, Cambridge. Admission is free, and doors will be open from 6.20pm.

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