^{#55 - Cesium}

Cesium, or Caesium, is atomic number 55. With the symbol Cs, it is quite an interesting element. It has a yellowish silver color, with and emission spectra of two shades of blue. (Its name originated from caesius, the latin word for sky blue.) It is the softest metal, with its hardness rating 0.2 on Moh’s scale, and it is, along with gallium and mercury, one of the three metals to be at its liquid state at or around room temperature. This is due to its low melting point of 28.5 degC (301.6 K, or 83.3 degF). (Its boiling point is low too, only at 678.4degC!) Generally speaking, elements that have a lower melting point also have a lower specific heat. This is true for cesium, with it having a specific heat of 0.24 J/gC. Although its melting point is so close to room temperature, its density is still measured at 20 degC, when it is in its solid state. Under these conditions, its volume density is 1.873 g/cm³. This is nearly double that of water, which is 1 on the same scale.

Cesium is in group 1a of the Periodic Table, which means that it is of the main group of alkali metals. Because cesium is the most alkaline of this group, it is the most alkaline of all of the elements. This means that a solution of cesium and water would form a very alkaline substance, which is a sign of high reactivity. Cesium’s electron configuration accounts for this. It has a total of six shells in its pure state, with the configuration being 2-8-18-18-8-1. This extra electron is released during reaction, making cesium a positive one ion. It reacts vigorously with air, hydrochloric acid, nitric acid, sodium hydroxide, hydroxide, oxygen, and water. When it reacts with hydroxide to form cesium hydroxide, it will form a very strong base and it will be able to destroy glass. It will react with oxygen to form Cs₂O, CsO, or CsO₂. It will also react vigorously with water, explosively with cold water. It is able to react with ice, if the ice’s temperature is above –116 degC. Unusually, this doesn’t affect the fact that cesium is non-toxic.

There are different places to acquire cesium naturally, even though it is a rare element. The french island of Elba has been discovered to have ores of the highest concentration of cesium oxide, which is a concentration of 34% cesium oxide. The United States has pollux in Maine and South Dakota, but this ore only has a concentration of 13% cesium oxide. Cesium can also be found in lepodolite, carnalite, and some types of feldspars. To remove the cesium from these ores, the cesium compound must first be extracted from the mineral. Then, the compound must be turned into cesium cyanide, or CsCN. Finally, the process of electrolysis puts the element into its pure form. Or, as an alternative method, the hydroxides or carbonates could be heated with aluminum or magnesium, and the chlorides could be heated with calcium.

There are many useful properties cesium retains that make it helpful in many situations. Its high reactivity with air makes it a good "getter," or a substance that helps remove air from a tube to create a vacuum tube. It is also useful in medicine. It releases more energy than radium, therefore it kills more cancer cells for better cancer treatment. Amazingly enough, this wonder element can also be used for clocks. Cesium’s stable form is Cs-133, which has 55 protons and 78 neutrons. In a cesium clock, microwaves are applied to cesium-133 until it vibrates at one of its resonant frequencies. This helps to keep a quartz clock at a pulse of 5 MHz. This entire device is enclosed and protected from the outer environment and from exterior magnetic fields. How well insulated and how precise these clocks are determines which of two classes they are in. One kind is a "laboratory standard," and the other is a "commercial standard." The lab standard is far better than the commercial standard, but the commercial version is less expensive, with some the relative size of a suitcase. These are often placed in clusters to produce an accurate mean time for scientific and public use.

In contrast, the lab standard is very large and is also very accurate, more so than the commercial version. It is unfortunately more expensive. The laboratory models are mainly used for research and measurements of extreme accuracy and precision. These clocks have a measurement error of one second per 1.4_*10⁶ years. It is the most accurate measurement man has achieved. This is why there are only a few in the world.

When we think of time or of medicine, we generally think of accurate and effective ways to do things. We may want a clock that keeps time precisely, or a method to kill cancer cells. In any case, we want something that has the properties needed to make such devices. In 1860, when German chemist Robert Bunsen and German physicist Gustav Kirchhoff discovered cesium through the use of a spectroscope, they were not aware of its possible uses. Cesium turned out to be an effective tool to create precise clocks and to kill cancer cells.

1. "Cesium." 16 Nov. 2000 http://www.chemicool.com/elements/cesium.html
2. "Cesium." Microsoft Encarta 97 Encyclopedia. ©1996 Microsoft Corporation
3. "Cesium Atomic Clocks." 16 Nov. 2000 http://tycho.usno.mil/cesium.html
4. "Periodic Table: Cesium." 16 Nov. 2000 http://www.chemicalelements.com/elements/cs.html
5. "Periodic Table – WebElements : caesium : key data." 16 Nov. 2000 http://www.webelements.com/webelements/elements/text/Cs/key.html

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