How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?
The electronic configurations of Na and Mg are:
11Na ; 1s22s22p63s1.
12Mg : 1s22s22p63s2
The first ionization enthalpy of sodium is lower than that of magnesium because the nuclear charge of Na (+11) is lower than that of Mg (+12) and size of Na is lower than Mg. After the loss of first electron, the electronic configuration of Na+ is 1s22s12p6 (has noble gas configuration) and Mg+ is 1s22s22p63s1. Hence removal of the second electron from Na+ is very difficult as compared to Mg+ (electron to be removed from 3s). Thus second ionisation enthalpy of sodium is higher than that of magnesium.
The first (IE1) and second (IE2) ionisation enthalpies (kJ mol-1) of a few elements by Roman numerals are as shown:
| IE1 | IE2 | |
| i | 2372 | IE2 |
| ii | 520 | 7300 |
| iii | 900 | 1760 |
| iv | 1680 | 380 |
which of the above elements is likely to be:
(i) a reactive metal
(ii) a reactive non-metal
(iii) a noble gas
(iv) a metal that forms a stable binary halide of the formula AX3 (X = halogen).
Among the elements of second period i.e. from Li to Ne, pick out the elements:
(a) with the highest first ionisation enthalpy
(b) with the highest electronegativity
(c) with the largest atomic radius
(d) which is the most reactive non-metal
(e) which is the most reactive metal ?
Which of the following pairs of elements would you expect to have lower first ionisation enthalpy? Explain your answer:
(a) Cl or F
(b) Cl or S
(c) K or Ar
(d) Kr or Xe.
Arrange the following in order of increasing ionisation enthalpies and assign reason:
(i) K+, Ar, Cl-
(ii) Fe, Fe2+, Fe3+
The first ionization enthalpy values (in kJ mol-1) of group 13 elements are:
B Al Ga In Tl
801 577 579 558 589
How would you explain this deviation from the general trend?
