Consequently the atomic and ionic radii decreases from La (57) to Lu (71) The outer electrons are attracted more by the nucleus. Thus the effective nuclear charge increases then the mutual shielding effect of (n-2) f electrons. The mutual shielding effect of (n-2) f electrons is very little because the shape of f-subshell is very much diffused. These two atoms contribute two electrons in the bond formation leaving behind half filled and completely filled 4 f-orbitals respectively.Ĭause of Lanthanide contraction – In lanthanides the additional electrons enters the (n-2) f orbital. Except Eu and Yb other lanthanides contribute three electrons in metallic bond formation. This is due to the difference in metallic bonding. There are two peaks one at Eu (63) and other at Yb (70). The decrease in size is regular in ions but not so regular in atoms. Inner transition elements – As we move along the lanthanide series, there is a decrease in atomic as well as ionic radius. The atomic radii of the elements of 3d transition series are as under. The atomic size from Cu to Zn slightly increases because shielding effect is more than the effective nuclear charge due to d 10 structure of Cu and Zn. The atomic size from the Fe to Ni almost remains the same because both the effects balance each other. In the first transition series the atomic size slightly decreases from Sc to Mn because effect of effective nuclear charge is stronger than the shielding effect. Thus moving from left to right in a period, there is a very small decrease in size and it may be considered that size almost remains the same. The atomic size increases due to shielding effect and balances the decrease in size due to increase in nuclear charge to about 80%. This effect of (n-1)d electrons over ns electrons is called shielding effect or screening effect. So the force of attraction between the ns electrons and the nucleus decreases. These (n-1)d electrons screen the ns electrons from the nucleus. In transition elements, electrons are filled in the (n-1)d orbitals. The atomic size first decreases due to the increase in effective nuclear charge and then becomes constant and then increases. ![]() ![]() For transition elements – There are four series of transition elementsĦd – Ac(89), Rf(104) ………….The Vander Waal’s radius of inert gases also increases on moving from top to bottom in a group. The atomic radius of inert gas (zero group) is shown largest in a period because of its Vander Waal’s radius which is generally larger than the covalent radius.For example the covalent radii of IA group elements in Å are as follows – Li Although the nuclear charge increases but its effect is negligible in comparison to the effect of increasing number of shells. (b)In a group, from top to bottom the number of shells increases. For example the covalent radii of second period elements in Å are as follows – Li ![]() (a) In a period from left to right effective nuclear charge increases because the next electron fills in the same shell.
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