The Alkali Metals
The Alkali Metals are the reactive elements in Group 1 of the Periodic Table, the consist of Lithium (Li), Sodium (Na), Potassium (K), Caesium (Cs) and Francium (Fr).
Reactions with Oxygen
The alkali metals are soft, shiny metals which react immidiately when in contact with oxygen in air - they tarnish, or corrode, forming a layer of the metal oxide on the surface. This is why they must be stored under oil, the alkali metals burn readily in oxygen. Eg:
Lithium + Oxygen -------> Lithium Oxide
4Li (s) + O2 (g) --------> 2Li2O (s)
The other metals react in similar ways, but the reactions become progressively more violent as you go down the group.
Reactions with Water
The alkali metals also react vigorously with water. Lithium fizzes on contact with water, forming the alkali lithium hydroxide and bubbles of hydrogen gas.
Lithium + Water --------> Lithium Hydroxide + Hydrogen
2Li (s) + H2O --------> 2LiOH (aq) + H2 (g)
The other alkali metals react in similar ways but again get progressively more violent as you go down the group. Sodium fizzes violently. Potassium creats so much heat as it reacts with water that it enlights the hydrogen gas, forming a lilac flame. The other metals are too reactive to carry out in a school lab.
Reactions with The Halogens
The halogens is the name given to the elements in Group 7 of the Periodic Table, including Chlorine and Bromine.
Lithium reacts readily in chlorine gas, producing the salt lithium chloride, LiCl:
Lithium + Chlorine -------> Lithium Chloride
2Li (s) + Cl2 (g) -------> 2LiCl (s)
Lithium reacts with bromine in a similar way, forming lithium bromide. The other alkali metals react similarley, and again the reactions become progressively more violent as you go down the group.
The reactions of the alkali meatls with oxygen, water and the halogens show us that the reactivity of them increase as you go down the group.