All alkali metals are highly reactive, so they form compounds easily and are found in many minerals. The walls of this potash mine have orange and white stripes due to the many potassium compounds being mined.
As well as hydrogen, the first column of the periodic table contains the alkali metals, a group of six elements that react vigorously with water to produce chemicals known as alkalis. Members of this group are soft enough to cut with a knife. They are never found pure in nature, but always as a compound, from which the pure metal is extracted.
Coloured flames Each alkali metal burns with a distinctive colour. While lithium burns with deep-red flames, potassium’s flames are lilac and sodium’s are yellow. Chemists look for these colours to identify the metals involved in reactions.
Easily tarnished
Freshly cut or scraped alkali metals are shiny, but turn dull as their surface reacts with oxygen in the air and forms a thin layer of the metal’s oxide. In laboratories, the metals are stored in oil to prevent this.
Highly reactive
Alkali metals are usually stored in oil because they are so reactive to the oxygen and water vapour in the air that some of them will burst into flames when they come into contact with it. Lithium tarnishes in the air, but doesn’t ignite until it is heated (as shown on the left). It combines with oxygen to form a whitish compound called lithium oxide.
Salt compounds
Alkali metals react with halogen elements to create salts, such as sodium chloride. These are white crystals that dissolve in water very easily. An example of this is sea salt, which is mostly sodium chloride, but also contains potassium chloride and trace amounts of other salts.
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