Introduction

The elements in which the last electron enters the outermost s-orbital are called s-block elements. s-block has two groups (1 and 2).

Diagonal Relationship

• The similarity in the properties of definite pairs of diagonally adjacent elements in the second and third periods of the periodic table is called diagonal relationship.
• In s-block elements Lithium is the first element of group 1 whereas Beryllium is the first elementsof Group 2.
• Some of their properties do not match with the properties exhibited by other elements of their group.
• Instead their properties resemble the properties of the second element of the following group due to the similarity in ionic sizes and /orcharge/radius ratio of the elements.
• Consequently lithium and magnesium have similar properties whereas Beryllium and Aluminium exhibit similar properties.
• This relation is called diagonal relationship.

• Both the elements are harder and lighter than the other elements.
• Both of them react slowly with
• The oxides and hydroxides of both the elements are less soluble.
• The hydroxides of both the elements decompose on heating.
• Both the elements form nitrides by combining directly with nitrogen.

6 Li+ N₂ (g) = 2 Li₃N

3 Mg(s) + N₂ (g) = Mg₃N₂(s)

• Both Li₂O and MgO do not produce their superoxide by combining with excess oxygen.
• Chlorides of both lithium (LiCl) and magnesium (MgCl₂) are soluble in ethanol, are deliquescent and crystallize as hydrates.

LiCl·2H₂O

MgCl₂·8H₂O

Atomic and Ionic Radii of alkali metals

• In Group 1 the atom of the atomic and ionic radii increases down the group.
• Increase in atomic number increases the size of the atom of the elements.