Alkali Metal

The alkali metals are the following chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr). The alkali metals are named this way because their reaction with water in which alkalis (strong bases) are formed. Hydrogen (H) is also placed in the group 1 but it does not belong to the alkali metals because it is a very specific chemical element with very different chemical and physical characteristics. Hydrogen is a gas at standard temperature and pressure. The alkali metals are malleable, ductile and are good conductors of heat and electricity. They can all be easily cut with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air because of oxidation.

Sodium and potassium are the sixth and the seventh most abundant elements, forming respectively 2.6 and 2.4 percent of Earth's crust. Rubidium, lithium and cesium form 0.03, 0.007 and 0.0007 percent of Earth's crust, respectively. Sodium and potassium estimated abundance in the ocean are 1.04x104mg/lit and 3.99x102mg/lit, respectively. Francium is very rare in nature due to its very high range of radioactivity.

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The alkali metals are generally found in nature combined with other elements forming minerals and salts. Some minerals, such as halite (NaCl, sodium chloride) and sylvite (KCl x MgCl2 x 6H2O, potassium-magnesium chloride) are soluble in water and therefore are easily extracted and purified. The more complex, water-insoluble minerals, are more abundant in Earth's crust. These metals react readily with atmospheric oxygen and water vapor. Lithium reacts with nitrogen, as well. Also, they react with water and thereby release hydrogen gas and form strong caustic solution. This reaction is vigorous and often violent. Sodium hydroxide and potassium hydroxide are known as very strong bases. The alkali metals react with inorganic substances such as halogens, halogen acids, sulfur, phosphorus and with organic compounds, particularly those containing a halogen or a readily replaceable hydrogen atom. The alkali metals form complete series of compounds such as hydroxides, intermetallic compounds, compounds with the group 13 and 14 elements, nitrides, oxides, chalcogenides, halides, coordination complexes, organometallics, etc.    

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The alkali metals have low level of electronegativity and electron affinity. Each of these metal atom has a single electron in its outer most shell and this valence electron is much more weakly bound than the electrons in inner shells. That is why they readily lose their outermost electron (ns1) to form cation with +1 charge. This way, they get the electronic configuration of a noble gas which is a preceding element in the periodic table. The oxidation number of each alkali metal is always +1. Chemically, the metals are all strong reducing agents. The ionization energy (the energy necessary to remove the outermost electron from the atoms of an element) decreases in periodic table toward the left and downward in each group. So, the alkali metals are the most easily ionizable elements in the periodic tables. They form ionic bond with non-metal elements from group 16 and 17 very easily. The alkali metals have very similar chemical properties due to the fact that their electronic configuration is ns1 in their outermost energetic shell.

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The melting points of the alkali metals as a group are lower than those in any other nongaseous group. They have low density, in fact lithium, sodium and potassium are the only three metals in the periodic table that are less dense than water. The number of stable isotopes is 2 for lithium, 1 for sodium, 2 for potassium, 1 for rubidium, 1 for cesium and francium has not stable isotopes.      

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The alkali metals have many different applications. Sodium chloride (NaCl) is actually table salt and it has been used since antiquity. Sodium and potassium are essential elements, having important biological roles as electrolytes. Lithium is used in medication and battery production. A common application of the sodium compounds is in the sodium-vapor lamp. Sodium is used as a heat transfer fluid in some nuclear reactors, as well. Very large quantities of commercial compounds that contain sodium are used worldwide, including salt (NaCl), baking soda (NaHCO3), sodium carbonate (Na2CO3) and caustic soda (NaOH). Potassium salts are very important in the manufacture of fertilizers. Atomic clocks are an example of a well-known application of rubidium and cesium. Finally, the alkali metals have application in alloys production as well as in other chemical production processes.

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