Question

First ionisation energy of alkali metals is very low but second ionisation energy is very high because

• A. alkali metals acquire noble gas configuration after losing one electron
• B. a large amount of energy is required to remove electron from a cation
• C. alkali metals can form only univalent ions
• D. first group elements can lose only one electron

Answer 1

Answer: (A)

alkali metals acquire noble gas configuration after losing one electron

Answer 2

All the alkali metals have one valence electron $n s^{1}$. outside the noble gas core. The loosely held s-electron in the outermost valence shell of these elements makes them the most electropositive metals. They readily lose electron to give monovalent $M ^{+}$ions. So, the first ionization energy of alkali metals is low. after the removal of one electron, i.e. formation of monovalent $M ^{+}$ ion, the metal atom attains noble gas configuration, so they require every high ionization energy to remove electron from stable noble gas configuration. Therefore the second ionization energy is very high as compared to first ionization energy.