ALKALI METAL
· Alkali metals
The metal of group IA like Li, Na, K, Rb, Cs and Fr dissolve in water to give metal hydroxide. They are ionized to give hydroxide ion and act a strong alkali. Therefore, group IA metal are called as alkali metal. The last element Fr is radioactive.
2Na + 2H2O ----------» 2NaOH + H2
NaOH ----------»Na+ + OH-
2K + 2H2O ----------» 2KOH + H2
KOH ----------» K+ + OH-
· Characteristics of Alkali metal
1) Electronic
configuration
Alkali meta has 1
electron in valence shell and has electronic configuration ns1 where
n represents number of shell.
Example: Li ----------»1s2,2s1
Na----------»1s2,2s22p6,3s1
K----------»1s2,2s22p6,3s23p6,4s1
2) Valency
and oxidation state
Due to the presence of only one
electron in the valence shell, it shows valency +1 and +1 oxidation states.
Na----------»Na+ + e-
3) Atomic
and ionic size
Alkali metals have
greater size in period and the size goes on increasing in a group.
4) Boiling point and melting point
Due to greater size of alkali metal, there is weak metallic bonding due to which melting point and boiling point is low.
5) Reactivity
Due to greater size of alkali metal, the valence electron can be removed easily. So that reactivity is high in period and it goes on increasing in group.
6) Flame colouration
Due to greater size of alkali metal, the valence electron are weakly attracted
by the nucleus. When alkali metal are heated in oxidizing flame, the valence
electron absorb heat energy and excited to higher energy level. But at higher
energy level, the electron are unstable so immediately, it returns back
to the ground state on doing. So, it emits the absorbed heat in the form
of radiation giving different colours to the flame.
Example: Li----------»Crimson color
Na----------»Golden yellow
K ----------» Purple
Rb----------»violet
· Na cannot be extracted from NaCl by using Carbon reduction process
1) Na itself is a strong reducing agents. So, it’s oxide and halide cannot be reduce by using Carbon
2) Na show greater affinity toward oxygen than that of Carbon
3) Carbon reduction process take place at high temperature at high temperature. Na combine with Carbon to form carbide
