Lithium is the lightest of all metals and is named from the Greek work for stone (lithos). It is the first member of the Alkali Metal family. It is less dense than water (with which it reacts) and forms a black oxide in contact with air.
Lithium was discovered in 1817 by Johan August Arfwedson but not isolated until some time later by W.T. Brande and Sir Humphry Davy.
In its mineral forms it accounts for only 0.0007% of the earth's crust. It compounds are used in certain kinds of glass and porcelain products. More recently lithium has become important in dry-cell batteries and nuclear reactors. Some compounds of lithium have been used to treat manic depressives.
In compounds lithium (like all the alkali metals) has a +1 charge. In its pure form it is soft and silvery white and has a relatively low melting point (181oC).
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Sodium is perhaps the most characteristic alkali metal, reacting violently with water and rapidly with the oxygen in air. It symbol (Na) comes from its Latin name, Natria, whereas its English name is taken from soda which contains it.
Sodium was discovered and isolated in 1807 by Sir Humphry Davy. In its pure form it is silvery white and soft enough to cut with a knife. It is the sixth most abundant element in the earth's crust, occurring in large amounts in both (sea)water and soil in various mineral compounds, the most common of which is sodium chloride.
The metal melts below the boiling point of water (97oC). In its elemental state it has been used as a molten coolant in nuclear reactors and is currently under research for sodium/sulfur batteries. Its most common compounds for industrial use include sodium chloride, sodium hydroxide (lye), sodium carbonate (washing soda) and sodium sulfate.
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Potassium reacts so violently with water that it bursts into flame. The silvery white metal is very soft and reacts rapidly with the oxygen in air. Its chemical symbol is derived from the Latin word kalium which means "alkali". Its English name is from potash which is the common name for a compound containing it.
The seventh most abundant element, potassium was discovered and isolated in 1807 by Sir Humphry Davy.
Important compounds of potassium include potassium hydroxide (used in some drain cleaners), potassium superoxide, KO2, which is used in respiratory equipment and potassium nitrate, used in fertilizers and pyrotechnics.
Potassium, like sodium, melts below the boiling point of water (63oC) and is less dense than water also. Like most of the alkali metals, potassium compounds impart a characteristic color to flames. In the case of the 19th element, the color is pale lavender.
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Like sodium ions, the presence of potassium ions in the body is essential for the correct function of many cells. Rubidium (Latin: rubidius = red) is similar in physical and chemical characteristics to potassium, but much more reactive. It is the seventeenth most abundant element and was discovered by its red spectral emission in 1861 by Bunsen and Kirchhoff. Its melting point is so low you could melt it in your hand if you had a fever (39oC). But that would not be a good idea because it would react violently with the moisture in your skin.
Rubidium was once thought to be quite rare but recent discoveries of large deposits indicate that there is plenty to use. However at present it finds only limited application in the manufacture of cathode ray tubes.
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Cesium is a bright silvery metal which is a liquid in a warm room (28oC). Its name is from the Latin caesius which is a description of a sky blue spectral emission by which it was discovered in 1860 by Bunsen and Kirchhoff.
Cesium is so reactive that it will even explode on contact with ice! It has been used as a "getter" in the manufacture of vacuum tubes (i.e., it helps remove trace quantities of remaining gases). An isotope of cesium is used in the atomic clocks.
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Francium is the last of the known alkali metals and does not occur to any significant extent in nature. All known isotopes are radioactive and have short half-lives (22 minutes is the longest).
The existence of Francium was predicted by Dmitri Mendeleev in the 1870's and he presumed it would have chemical and physical properties similar to cesium. That may well be, but not enough francium has been isolated to test.
Numerous historical claims to the discovery of element 87 were made resulting in the names russium, virginium, and moldavium. However, the confirmed discovery is credited to Marguerite Perey who was an assistant to Marie Curie at the Radium Institute in Paris. She named the element after her native country.
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