(i) The vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
(ii) Based on the common characteristics of elements in each group, they can be grouped as various families.
(iii) The Lanthanides and Actinides, which form part of Group 3 are called inner transition elements.
(iv) Except ‘group O’, all the elements present in each group have the same number of electrons in their valence shell and thus have the same valency.
Eg: all the elements of group 1 have one electron in their valence shells (Is ).
So, the valency of all the alkali metals is ‘ 1’.
(v) As the elements present in a group have identical valence shell electronic configurations, they possess similar chemical properties.
(vi) The physical properties of the elements in a group such as melting point, boiling point and density vary gradually.
(vii) The atoms of the ‘group 0’ elements have stable electronic configuration in their valence shells and hence they are unreactive.
