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.
(a) Cl or F: Chlorine is expected to have lower IE1 as compared to fluorine since ionisation enthalpy decreases down a group. Chlorine comes after fluorine in group 17 of the periodic table.
(b) Cl or S: Sulphur is expected to have lower IE1 as compared to chlorine since ionisation enthalpy increases along a period. Chlorine having smaller size than sulphur comes after sulphur in the third period.
(c) K or Ar: Potassium is expected to have lesser IE1 than argon (noble gas-element) because the configuration of argon is very much symmetrical stable. Hence argon has a very high IE, value.
(d) Kr or Xe: Both the elements belong to group 18 (noble gas family). As we know ionisation enthalpy decreases down the group, thus xenon comes after krypton has lesser IE1 value.
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?
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 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 ?
