👇 Download Handwritting Notes 👇
DOWNLOAD PDF
Points
INTRODUCTION
The s-block elements of the Periodic Table are those in which the last electron enters in the outermost s-orbital.
As the s-orbital can accommodate only two electrons, two groups (1 & 2) belong to the s-block of the Periodic
Table. Group 1 of the Periodic table consists of the elements: lithium, sodium, potassium, rubidium, cesium and
francium. They are collectively known as the alkali metals. They are so called because they form hydroxides on
reaction with water which are strongly alkaline in nature. The elements of Group 2 include Beryllium, Magnesium,
Calcium, Strontium, Barium and Radium. These elements with the exception of beryllium are commonly
known as the alkaline earth metals. They are so called because their oxides and hydroxides are alkaline in
nature and these metal oxides are found in the earth's crust
ANOMALOUS BEHAVIOR OF LITHIUM
l On account of its small size it exerts the greatest polarising effect out of all the alkali metals and ions, consequently
covalent character is developed.
l Li has the highest ionisation energy and electronegativity as compared to other alkali metals.
l It is not affected by air easily and does not lose its lusture even on melting.
l It is more harder and lighter than other alkali metal.
l It reacts slowly with water to liberate hydrogen.
l When burnt in air or oxygen, it forms only monoxide, Li2O. However, the rest of the alkali metals give peroxide
or superoxides.
l Li2O is less basic oxides than of other alkali metals.
l Lithium hydroxide decomposes when red heated to form Li2O. Hydroxides of other alkali metals do not decompose.
2LiOH ¾¾D ® Li2O + H2O
l Li2CO3 is less stable, as it decomposes on heating. Li2CO3
¾¾D ® Li2O + CO2
l Li2SO4 is the only alkali metal sulphate, which does not form double salts Ex. Alum.
l Li when heated in NH3 forms imide Li2NH while other alkali metals form amides. MNH2
l Lithium shows resemblance with magnesium, an element of group IIA.
This resemblance is termed as diagonal relationship.
Similariteis between lithium and Magnesium
(i) Both lithium and magnesium are harder and lighter than the other elements in their respective groups.
(ii) Lithium and magnesium reacts slowly with cold water. Their oxides and hydroxides are much less soluble
and their hydroxides decomposes on heating. They both form nitride by direct combination with nitrogen,
Li3N and Mg3N2.
(iii) The oxides, Li2O and MgO do not combine with excess oxygen to give a peroxide or a superoxide.
(iv) The carbonates of lithium and magnesium decomposes easily on heating to form the oxide and CO2.
Solid bicarbonates are not formed by lithium and magnesium.
(v) Both LiCl and MgCl2 are soluble in ethanol.
(vi) Both LiCl and MgCl2 are deliquescent and crystallise from their aqueous solution as hydrates,
LiCl.2H2O and MgCl2.8H2O
ANOMALOUS BEHAVIOR OF BERYLLIUM
l It is the hardest of all alkaline earth metal as maximum metallic bonding is there due to it's smallest size.
l The melting and boiling points of the beryllium are the highest.
l It is least reactive due to highest ionisation potential.
l Due to high charge density its polarising effect is highest and it forms covalent bond.
l It dissolves in alkalies with the evolution of hydrogen
Be + 2NaOH + 2H2O Na2BeO2.2H2O + H2
Sodium beryllate
other alkaline earth metals do not react with alkalies.
l Oxides and hydroxides of beryllium are amphoteric in nature.
BeO + H2SO4 ® BeSO4 + H2O BeO + 2NaOH ® Na2BeO2 + H2O
Be(OH)2 + 2HCl ® BeCl2 + 2H2O Be(OH)2 + 2NaOH ® Na2BeO2 + 2H2O
The hydroxide is Insoluble in water and is covalent in nature.
l Like Al4C3, its carbide (Be2C) on hydrolysis evolves methane.
l Due to its small size it has strong tendency to form complex.
l It shows diagonal relationship with Al
0 Comments