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As you go down the left-most column of elements in the periodic table, they become progressively more reactive. Lithium bubbles slowly in water, sodium bubbles faster and usually explodes, potassium definitely explodes. By the time you get to rubidium, its to the point where even the moisture in the air can be enough to set it off. Rubidium also has a very low melting point, so if it gets going it quickly turns into a liquid, greatly increasing the rate of reaction. For this reason rubidium must be kept in sealed glass ampules or under an inert gas atmosphere.
There are not a lot of industrial uses for rubidium, but one of them is as a time standard. Electronic transitions in the atoms in a rubidium vapor are used as a very, very stable frequency reference: You can buy such modules for less than a hundred dollars on eBay, for example. Cesium is also used for this purpose, but cesium time standards are more expensive.
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Sealed ampule.
Rubidium is much like cesium in that it's a solid at room temperature, but liquid just a bit higher. Cesium actually melts in your hand, while rubidium needs to be just a bit warmer. Cesium also has a much prettier color, exactly the color of gold.
They would both, however, explode on contact with moist air, so we keep them both safely locked up.
Click the source link for an interesting story about where this sample came from.
Source: Tryggvi Emilsson and Timothy Brumleve
Contributor: Tryggvi Emilsson and Timothy Brumleve
Acquired: 6 September, 2002
Price: Donated
Size: 2.5"
Purity: 99.9%
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Sample from the Everest Element Set.
Up until the early 1990's a company in Russia sold a periodic table collection with element samples. At some point their American distributor sold off the remaining stock to a man who is now selling them on eBay. The samples (excepted gasses) weight about 0.25 grams each, and the whole set comes in a very nice wooden box with a printed periodic table in the lid.
To learn more about the set you can visit my page about element collecting for a general description and information about how to buy one, or you can see photographs of all the samples from the set displayed on my website in a periodic table layout or with bigger pictures in numerical order.
Source: Rob Accurso
Contributor: Rob Accurso
Acquired: 7 February, 2003
Price: Donated
Size: 0.2"
Purity: >99%
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