Wednesday, 1 July 2015

Mendeleev Periodic Law, Modern Periodic Law and s, p, d, f - Block Elements

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.

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