Short Answer Type
Long Answer TypeWhich 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.
Short Answer TypeAmong 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 ?
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).
Long Answer TypeThe IE1, of carbon, is more than that of boron while its IE2 value is smaller. Explain.
Short Answer TypeArrange the following in order of increasing ionisation enthalpies and assign reason:
(i) K+, Ar, Cl-
(ii) Fe, Fe2+, Fe3+
(i) K+, Ar, Cl-:
The correct order is Cl- < Ar < K+.
All the three species are isoelectronic, each containing 18 electrons. The nuclear charge increases in the order Cl- (+17) < Ar (+18) < K+ (+19). As the nuclear charge increases, the attractive force between the nucleus and the same number of electrons also increases. This results in the decrease of size and hence ionisation enthalpy increases.
(ii) Fe, Fe2+, Fe3+:
The correct order is Fe < Fe2+ < Fe3+.
In the formation of the cation from the atom, electrons are removed. As a result, the effective nuclear charge increases and so is the ionisation enthalpy. Greater the magnitude of positive charge on the ion, more will be its ionisation enthalpy. Hence the order is justified.
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 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?
Switch
