Mandeleev’ s Periodic Law:- The properties of the elements are the periodic function of their atomic masses.
Moseley, the English physicist showed that atomic number is more fundamental property of an element than its atomic mass. Therefore, the position of an element in the periodic table depends on its atomic number than its atomic mass.
Modern Periodic Law: The physical and chemical properties of elements are the periodic functions of their atomic numbers.
Types of Elements: s-, p-, d- and f- blocks.
MAIN GROUP ELEMENTS / REPRESENTATIVE ELEMENTS:
The s- and p- block elements are called main group elements or representative elements.
s- block elements: Group-1( Alkali metals) and Group-2 elements( Alkaline earth metals) which respectively have ns 1 and ns 2 outermost electronic configurations.
p- Block elements: They belongs to group- 13 to 18. The outer most electronic configuration is ns 2 np 1-6. He( 1s 2) is a s- block element but is positioned with the group 18 elements( ns 2 np 6) because it has completely filled valence shell and as a result, exhibits properties characteristic of other noble gases.
d- block elements( Transition elements) are the elements of group 3 to 12
having outer electronic configuration( n-1) d 1-10 ns 1-2. Four transition series are 3d, 4d, 5d and 6d. The 6d- series is incomplete. Atomic radius generally decreases across a period and increases as we descend the group.