Question

can someone please tell me what shielding effect is and how it works..??

Answer 1

It's referring to the decrease in attraction between an electron n the nucleus in an atom with more than one electron shell.
a 3s2 3p4

the 4 electrons in the p-orbital experience the attraction from the nucleus (positive), but also experience the repulsion from the electrons (negative) in the 2s orbital.
Without going into quantum chemistry, that's the basic idea behind shielding.

Answer 2

when there is one electron in a shell in an atom for eg hydrogen then the total attractive force from the nucleus is concentrated totally in that one elctron but as the no. of electrons in the outer shells increases, the electrons actually act as a screen or curtain for the outermost electron to have the total attractive force from the nucleus due to repulsions from the inner electrons this is known as screening effect or shielding effect... now there's a rule called Slater's rule by which we can measure how much the total effective charge from the nucleus is actually acting on that electron .... the d - electrons exhibit weaker screening effect....
actually this is the main reason behind inert pair effect(this weaker screening)

Answer 3

thanx guys.... :)