Mendeleev Periodic Law
Mendeleev explanation that properties of the elements are periodic function of their atomic weights.
Modern Periodic Law
Moseley (1913) according to this law physical & chemical properties of the elements are periodic functions of their atomic numbers.
S – Block Elements
Elements of group 1 (Alkali metals) with ns2 outermost electronic configuration.
· These are all reactive metals with low ionisation enthalpies.
· They lose electrons rapidly to form +1 & +2 ions.
· Metallic character and reactivity increases on going down the group.
P – Block Elements
These elements belong to group no. 13 to 18.
· These with s – block elements are called representative elements.
· Outermost electronic configuration is varies from ns2 np1 to ns2 np6.
· Element of group 18 (ns2 np6) are known as noble gases or invert gases.
· Elements of group 17 known as halogens and elements of group 16 known as chalcogens.
· Group 16 & 17 elements have high -ve electron in their outermost shell to attain stable inert gas configuration.
· Non-metallic character increase on moving left to right in period and metallic character increases on moving down in the group.
D – Block Elements
These are elements of group no. 3 to 12 in centres of periodic table. Also known as the transition elements.
· General outer most electronic configuration is (n-1)d1-10 n0-2
· These are all metals
· Form colours ions and show variable valences & par magnetism
· Mainly used as a catalyst
· Zn , cd , Hg with configuration (n-1)d10 ns2 do not show most of the properties of transition elements.
F – Block Elements
These have 2 – rows of elements at bottom of periodic table. i.e. lanthanides Ce (z = 58) to Lu (z = 71) Actinides Th (z = 90) to Lr (z = 103) .
· Outer electronic configuration =(n-2) f1-14(n-1) d0-1 ns2.
· f – block elements also known as inner transition elements.