The metals in Group I of the periodic table are called the alkali metals. They are:
Properties of alkali metals:
The alkali metals have the high thermal and electrical conductivity, lustrous, ductile, and malleable that are characteristic of metals.
The alkali metals are softer than most other metals.
They have low melting points
Lower densities than other metals
Alkali metals do not occur in nature as elements.
They are called alkali metals because they react with water to form alkaline solutions. For example:.
- sodium + water sodium hydroxide + hydrogen
- 2 Na + 2H2O 2 NaOH + H2
This group lies in the s-block of the periodic table. Each alkali metal atom has a single electron in its outermost shell (s-orbital), which is loosely bound. This gives alkali metals the largest atomic radii in their periods.
Alkali metals are highly reactive metals. The reactivity increases on moving down the Group from lithium to cesium. That means as their atomic numbers increase the furthur down they appear in the group, their reactivity increases.
Alkali metals have low electronegativities.
Alkali metals have low ionization energies.
They react readily with nonmetals, particularly halogens.
Oxides are formed when an alkali metal comes in contact with air or oxygen. Oxides of alkali metals are basic in nature and are soluble in water and form alkali metal hydroxides.
- sodium + oxygen sodium oxide
- 4 Na + O2 2 Na2O
When alkali metals react with hydrogen, ionic hydrides are formed. These hydrides have basic and reducing properties. The ionic nature of the hydrides increase as we move down the Group from lithium to caesium. The stability of these hydrides reduces with the increase in the atomic numbers of alkali metals.
- sodium + hydrogen sodium hydride
- 2 Na + H2 2 NaH
When alkali metals react with halogens, halides are formed. All the halides readily dissolve in water except lithium fluoride (LiF). All the halides are ionic in nature except lithium iodide.
- The chemical reaction of the alkali metals with the halogens is:
- 2 M + X2 2 MX (where M represents an alkali metal and X represents a halogen)
When alkali metals react with nitogen, nitrides are formed.
- The chemical reaction of lithium with nitrogen is:
- 6 Li (s) + N2 (g) 2 Li3N (s)