Question

1. What is screening effect ? Explain how it affects the ionization potential and atomic radius of an atom ?

2. Calculate the electronegativity of O according to Pauling scale, Mulliken scale and Allred-Rochow scale.

Thanks

Answer 1

The screening effect or shielding effect is the phenomena by which the inner shell electrons repel the outershell electron and shield them from the attraction of the nucleus.

Higher the electron density in the inner shell, higher will be the electron-electron repulsion and hence higher will be the shielding effect of the inner shell electrons. Smaller the size of orbital in the inner shell, higher will be the density of electrons. Hence higher will be the shielding effect of the inner shell electrons.

Electrons in a subshell also repel each other and hence shield each other from the nucleus. The shielding of the electrons in the subshell is smaller than the shielding effect of inner shell electrons on the outer shell electrons. Shielding effect increases with increase in the number of electrons in the inner shell or in the outermost shell.

The atomic radius increases down the group and decreases along the period because along the period the electrons are being added in the same subshell and there is not an increase in the number of shells bt down the group the number of shells are increasing and it dominates the screening affect of the nucleus on the outer most electrons and the screening effect of the inner shell electrons are more due to the high electron density in the inner shell which causes more repulsion and so increase in the atomic radius but along the period the number of shells are same but the nuclear charge is increasing which has a dominated screening effect on the outer most shell electrons as compared to the screening effect of inner shell electrons.

Ionization potential is the potential difference required to remove an electron from an isolated gaseous atom to obtain a unipositive cation is called ionization potential(Ip).The energy corresponding to the ionization potential is called ionization energy. So along the period the screening effect of nucleus increases on the outemost shell so the ionization potential also increases. And down the group the screening effect of inner shell electrons dominates so ionization potential decreases.

The ability of a molecule to attract bond pair of electrons towards itself resulting in partial negative charge on itself and a partial positive charge on the adjacent atom is called electronegativity of that atom

To calculate the electronegativity of O we must have it in bonding with another atom to form a molecule as electronegativity is not the property of an isolated atom in gaseous state. The formulae to calculate the electronegativity are shown in the image