Four elements are selected from Periods 2–4 of the periodic table

CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends

Problem

Four elements are selected from Periods 2–4 of the periodic table.

Element	Atomic Number	Valence-shell Configuration (ground state)
N	7	$2s^2 2p^3$
O	8	$2s^2 2p^4$
P	15	$3s^2 3p^3$
As	33	$4s^2 4p^3$

Assume that all elements are in their gaseous ground states. (a) Rank the four elements from lowest to highest first ionization energy. Clearly indicate any equalities if you believe two ionization energies are approximately the same. (b) Provide a detailed justification for your ranking that explicitly discusses (i) the change across a period and (ii) the change down a group. (c) The second ionization energy (

I_2

) removes another electron from the same atom after the first has been removed. Predict which element, N or O, will have the larger

I_2

and explain your reasoning with reference to electron configurations and relative stability. (d) Suppose arsenic is photo-ionized to form As

^{+}

. Compare qualitatively the effective nuclear charge experienced by the electron that is removed in forming As

^{2+}

with that experienced in forming As

^{+}

. Explain how this comparison relates to the expected magnitude of

I_2

for arsenic.

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