will have a smaller radius because of the greater attraction of the electrons to the nucleus. Anion with the greater negative charge will have the larger radius. In this case, the net repulsion of the electrons will outweigh the nuclear charge and the ion will expand in size. Problem .
Which of the following species will have the largest and the smallest size? Mg, Mg + , Al, Al + . Atomic radii decrease across a period. Cations are smaller than their parent atoms.
Among isoelectronic species, the one with the larger positive nuclear charge will have a smaller radius. Hence the largest species is Mg; the smallest one is Al + . (c) Ionization Enthalpy A quantitative measure of the tendency of an element to lose electron is given by its Ionization Enthalpy . It represents the energy required to remove an electron from an isolated gaseous atom (X) in its ground state.
* Two or more species with same number of atoms, same number of valence electrons and same structure, regardless of the nature of elements involved. In other words, the first ionization enthalpy for an element X is the enthalpy change ( ∆ i H ) for the reaction depicted in equation . . X(g) → X + (g) + e – ( .
) The ionization enthalpy is expressed in units of kJ mol – . We can define the second ionization enthalpy as the energy required to remove the second most loosely bound electron; it is the energy required to carry out the reaction shown in equation . . X + (g) → X + (g) + e – ( .
) Energy is always required to remove electrons from an atom and hence ionization enthalpies are always positive. The second ionization enthalpy will be higher than the first ionization enthalpy because it is more difficult to remove an electron from a positively charged ion than from a neutral atom. In the same way the third ionization enthalpy will be higher than the second and so on. The term “ionization enthalpy”, if not qualified, is taken as the first ionization