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Classification of Elements and Periodicity in Properties

Short Answer Type

131.

Nitrogen and phosphorus have high value of ionisation enthalpies. Explain.

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132.

Be and Mg have high value of ionisation enthalpies. Explain.

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133. Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

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Long Answer Type

134.

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.

294 Views

Short Answer Type

135.

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 ?

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136.

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).

183 Views

Long Answer Type

137.

The IE₁, of carbon, is more than that of boron while its IE₂ value is smaller. Explain.

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Short Answer Type

138.

Arrange the following in order of increasing ionisation enthalpies and assign reason:

(i) K⁺, Ar, Cl^-(ii) Fe, Fe²⁺, Fe³⁺

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139.

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?

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140.
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?

The decrease in first ionization enthalpy (∆_IH₁) value from B to Al is due to the bigger size of Al atom. But the element Ga has ten 3d electrons present in the 3d sub-shell which does not screen as much as is done by s and p electrons. Therefore there is an unexpected increase in the magnitude of effective nuclear charge resulting in increased ∆_iH₁, value. The same explanation can be given in moving from In to TT. The latter has fourteen 4/ electrons with very poor shielding effect. This also results in an unexpected increase in the effective nuclear charge resulting in inflated ∆_IH₁ value.

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