Observe the following graph for ionisation enthalpies of first, second and third transition series…
Chemistry20253 marksCase based
Observe the following graph for ionisation enthalpies of first, second and third transition series.
(a)[1.0]
Why does the ionisation energy increase across a transition series?
(b)[1.0]
The ionisation energies are nearly equal for first and second transition series but abruptly increases for third transition series. Explain.
(c)[1.0]
Which element would have higher density, technetium or rhenium? Justify your answer.
Answer
Answer (a)
Official answer key
Ionisation energy increases with increase in nuclear charge which increase with increase in atomic number. The added electron shields the added proton. The effect of increased nuclear charge is more than the shielding effect.
Answer (b)
Official answer key
In the third transition series, after lanthanum, lanthanoids have electrons entered in 4f orbital, which shows poor shielding effect, hence atomic size decreases due to lanthanoid contraction, ionisation energy increases abruptly for decreased atomic size.
Answer (c)
Official answer key
Rhenium has higher density due to decreased atomic size and increase in nuclear charge. Hence, the atomic volume decreases and electron density increases.
