Q.Give reasons.
a. Alkali metals have low ionization enthalpies.
b. Inert gases have exceptionally high ionization enthalpies.
c. Fluorine has less electron affinity than chlorine.
d. Noble gases possess relatively large atomic size.
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Start your 14-day free trial to unlock the full solution →Step 1a. Alkali metals' low IE. Alkali metals have only one valence electron () sitting in a large outer shell heavily shielded by a full inner core, giving a very low effective nuclear charge on that electron — so very little energy is needed to remove it (Table 7.3 confirms the lowest IE in every period belongs to its alkali metal).
Step 1b. Inert gases' high IE. Inert gases have a completely-filled, exceptionally stable valence shell (a full octet, or a full duplet for He); disturbing this unusually stable arrangement by removing an electron requires far more energy than for any other element in the same period, giving inert gases the highest IE of their period (Table 7.4: Ne at 2080 kJ mol⁻¹, the period-2 maximum).
Step 1c. Fluorine's electron gain enthalpy. Although F is smaller and more electronegative than Cl, its very small 2p subshell is already electron-dense, so the incoming extra electron experiences significant electron-electron repulsion there, which partly offsets the energy released on adding it. Chlorine's larger 3p subshell accepts the extra electron with comparatively less repulsion. The net result is that fluorine's electron gain enthalpy is LESS negative than chlorine's, i.e. chlorine has the higher electron affinity of the two — matching the reasoning already used in Problem 7.7 for the Cl-vs-Br comparison, applied here one further step to F-vs-Cl. …
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