THE ALKALI METALS GROUP 1 A

The alkali metals are soft metallic solids ( FIGURE 7.19). AH have characteristic metallic properties, such as a silvery, metallic luster and high thermal and electrical conductivity. The name alkali comes from an Arabic word meaning ashes. Many compounds of sodium and potassium, two alkali metals, were isolated from wood ashes by early chemists. 

The alkali metals exist in nature only as compounds. Sodium and potassium are relatively abundant in Earths crust, in seawater, and in biological systems, usually as the cations of ionic compounds. All alkali metals combine directly with most nonmetals. For example, they react with hydrogen to form hydrides and with sulfur to form sulfides  

The alkali metals react vigorously with water, producing hydrogen gas and a solution of an alkali metal hydroxide  

These reactions are very exothermic. In many cases enough heat is generated to ignite the H2, producing a fire or. sometimes even an explosion ( FIGURE 7.20). The reaction is most violent for the heavier alkali metals, in keeping with their lower ionization energies. 

A FIGURE 7.19 Sodium, lire the other airali metals, is soft enough to be cut with a knife. 

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