why the shielding effect does not comes into play period when electrons keep on adding in the same shell, then why don't due to shielding effect the attraction on the outermost shell decreases, and leading to increase in atomic size? Why it happens vice versa? Explain?
Dear Student,
The shielding effect of electrons is the protection of outermost electrons from the attraction of nucleus due to the increasing number of inner electrons
. On moving across the period the atomic number increases but the subsequent electrons are added in the same principal shell . This creates a repulsion between the electrons but with the increasing atomic number we have to keep in mind that the number of protons in nucleus is also increasing and so the effective nuclear charge also increases. The effect of nucleus dominates over repulsion and the electrons are pulled towards the nucleus leading to a decreased atomic size.
But down the group with increasing atomic number the principal shell also increases. The subsequent electrons are filled in accordance with afbau principle . Thus the number of inner shell electrons also increases and builds a wall between nucleus and valence electrons. The nucleus cannot effectively attract the electron .Hence atomic size increases due to shielding effect and increase in number of shells.
Regards!
The shielding effect of electrons is the protection of outermost electrons from the attraction of nucleus due to the increasing number of inner electrons
. On moving across the period the atomic number increases but the subsequent electrons are added in the same principal shell . This creates a repulsion between the electrons but with the increasing atomic number we have to keep in mind that the number of protons in nucleus is also increasing and so the effective nuclear charge also increases. The effect of nucleus dominates over repulsion and the electrons are pulled towards the nucleus leading to a decreased atomic size.
But down the group with increasing atomic number the principal shell also increases. The subsequent electrons are filled in accordance with afbau principle . Thus the number of inner shell electrons also increases and builds a wall between nucleus and valence electrons. The nucleus cannot effectively attract the electron .Hence atomic size increases due to shielding effect and increase in number of shells.
Regards!