This means we can actually see, hold and play with the most reactive metallic element that nature has given us. ![]() Caesium on the other hand, is readily obtainable, and in its protective environment will last forever. This is great since francium can only be made in miniscule proportions and then only lasts for a few minutes so you'll never see any. This means that despite what you may hear, or might have expected, caesium is the most reactive metal. Remarkably, this experiment has been carried out and the prediction has been confirmed. Theory predicts that the atoms begin to get slightly smaller and that it is actually harder to remove the outermost electron from francium than it is for caesium. In order to understand why, you would need to take into account Einstein's relativistic effects. It turns out for really heavy elements, the electrons begin to get slightly harder to remove than expected. They also said that the element beneath caesium in the periodic table, francium, would be even more reactive. Actually, they faked the reaction of rubidium and caesium with water since they thought they were not spectacular enough for TV. One pseudo-science programme on TV showed the reaction between water and the different group one alkali metals, namely lithium, sodium, potassium, rubidium and caesium. This means the element for which it is easiest to remove an electron and form a cation, is in the bottom left-hand corner of the periodic table, where caesium is found. What's more, on moving across the periodic table, from group one with lithium, sodium, potassium etc to group two with beryllium, magnesium, calcium and so on, it becomes increasingly harder to remove the outermost electrons. It is its willingness to lose an electron completely and form a positively charge ion that makes caesium the most reactive metal in the periodic table, and yes I am including its relative francium! All the alkali metals are reactive because they have one outermost electron which is easily removed but on moving down the group, the atoms get larger and larger and this outermost electron gets on average further and further away from the positively charged nucleus. So called caesium atomic clocks are accurate to one second in more than a million years and are used when precision timing is crucial, for instance in tracking the space shuttle. It is another electronic transition in caesium that gives us the most accurate clocks on earth. They named the new element caesium because of the distinct blue lines in the spectrum. When examining the spectrum of the residue from some spa mineral water, Bunsen and Kirchhoff found a series of lines that did not correspond to any known element. Each element has its own unique spectrum of lines, like a rainbow barcode. The spectroscope splits up the light with a prism and reveals a spectrum consisting of series of sharp coloured lines. When they return to their lower energy states, energy is released in the form of light. When atoms are energetically excited, for instance when a compound is introduced into a flame, electrons can temporarily be promoted to higher energy levels. The previous year they had invented an instrument known as a spectroscope to help in chemical analysis. ![]() Caesium was discovered in 1860 by Robert Bunsen (he of the burner fame) and physicist Gustav Kirchhoff. ![]() Not for its eyes (it's only an element!) but less romantically for the appearance of its emission spectrum in the spectroscope. Source: Universitätsbibliothek Heidelberg – CC BY-SA 4.0Ĭaesium gets its name from the Greek for heavenly blue. So to play with it, you have to hold the glass tube, knowing that if you accidentally crushed it, or dropped it, all hell would break loose. My caesium is sealed inside a glass tube under an atmosphere of the chemically inert gas argon. In fact, you can't actually touch the metal itself since it spontaneously bursts into flames in the presence of air and reacts explosively with water. Liquid metals are always fascinating – everyone loves mercury just imagine playing with liquid gold!īut here's the snag that adds to my fascination with this metal - it has a rather fiery temper. So just holding its container converts the crystalline solid into liquid gold. Strictly speaking, it's the warmth from the hand that melts it, given that its melting point is only 28.4☌. The next exciting thing about caesium is that my love is not unrequited, it responds to my touch. The Royal Society of Chemistry and Compound Interest are celebrating IYPT with these element graphics, which will be released throughout the year Source: © Andy Brunning/Royal Society of Chemistry
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