What is electron shielding and what impact does it have on atomic radius?

Answer 1

The electrons in the atom surround the nucleus, and the higher the atomic number of the element the more electrons there are. Unless it is ionised, there will be an equal number of protons in the nucleus and electrons surrounding the atom. Ideas of how the electrons are arranged have evolved from imagining them to be in orbit around the nucleus, like a small solar system, to modern ideas of quantum physics where it is best to imagine them as an electron 'cloud'. However the idea of electron shells is still useful, this is as imagined by Bohr in the twenties of the last century, where concentric shells contain fixed numbers of electrons according to strict rules on their composition. Your query on 'electron shielding' is probably to do with these electron shells, and the more shells there are determines the effective size of the atom. You can read more in the link below

Answer 2

First off, it's important to remember that electronegativity is an atomic property within a molecule, not in its free form. If you think of it like that, it makes complete sense that the further an atom's valence electrons are from the nucleus, the weaker the electromagnetic bond between it and the nucleus, and therefore the less likely it will want to take in another electron, ie., lower electronegativity. The valence electron's own electromagnetic field repulses other electrons, and the further they are from the nucleus, the stronger the repulsive force is compared to the nucleus' attractive force.