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 .