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Alkali Metals: General Characteristics And Properties

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Alkali Metals: General Characteristics And Properties - Lesson Summary



Group 1 metals are also called as alkali metals. These are the most reactive metals. They contain only one electron in its valence shell thus they form +1cations.

The alkali metals are good conductors, and they have a shiny, silvery appearance. In flame tests, lithium forms a candy-apple red colour, while sodium produces a yellow flame and potassium a lilac flame.

Chemical properties:
They react with hydrogen to form metal hydrides.
2M + H 2 → 2MH
(Where M= Li, Na, K, Rb, Cs)

They react with halogens to form alkali metal halide salts, such as NaCl.
2Na + Cl 2 → 2NaCl

They react with oxygen lithium forms oxides, sodium forms peroxides, and the other group 1 metals form superoxides.
4Li + O 2 → 2Li 2O (Lithium oxide)
2Na + O 2 → Na 2O 2 (Sodium peroxide)
M + O 2 → MO 2
Where M = K, Rb, Cs
 
Alkali metals react vigorously with water to produce hydroxide ions in solution, and hydrogen gas. 

Applications:
  • An alloy with lead is used to make engine parts, an aluminium-lithium alloy is used in airplane construction and a magnesium-lithium alloy is used to make armour plates.
  • Lithium metal is used in some thermonuclear reactions and to construct various types of batteries.
  • Sodium-lead alloy was used to produce organo-lead compounds such as tetraethyl lead, which was used as an anti-knock agent in automobile fuel. 
  • Potassium has a variety of roles in biological systems.  Potassium chloride is used as an agricultural fertiliser under the name ‘muriate of potash’.
  • Cesium is used in the manufacture of photoelectric cells.

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