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Polarizability and polarizing power
The symmetrical pictures of atomic electron clouds that you have seen apply only to isolated atoms and ions in the presence of an external electrostatic field these electron cloulds will be deformed with the electron density being concentrated toward a positive charge and away from a negative charge polarizability is a measure of the ease with which an external electric field is able to distort the charge clould of an atom or molecule (thus polarizability is not exclusively an atomic property ) the external field can come from a nearby ion . or even from the polar end of a molecule that is electrically neutral but does not have its electron cloud distributed evenly in genral large species and especially large negative ions are more polarizable than smaller species the less polarizable an ion is the greater is its polarizing power ions with a high charge density or charge per unit volume exhibit the greatest polarizing power . thus a small ion
Such as li is more polarizing than k + for example h+ is the most polarizing ion of all owing to its minute volume as a bare proton polarizability and polarizing power are correlated with many aspects of chemical behavior and they provide an important link between this behavior and the position of the element in the
Periodic table polarizability is also important for understanding some of the
Physical properties of substances in uncharged species sush as the noble gas
Distribution act to polarize adjacent atoms or the molexules creating a net attractive force that increases with the polarizabitity of the molecule this is the origin of the universal weak attraction that is responsible for holding molecules together in the liquid and solid stares in the absence of any more direct attractive forces