Question
Chemistry Question on Classification of elements & periodicity in properties
The correct order of the first ionization enthalpy is
A
Al > Ga > Tl
B
Ga > Al > B
C
B > Al > Ga
D
Tl > Ga > Al
Answer
Tl > Ga > Al
Explanation
Solution
(i) Due to the lanthanide contraction, thallium (Tl) has a higher first ionization enthalpy compared to gallium (Ga) and aluminum (Al). This is because the contraction results in a higher effective nuclear charge, which increases the ionization energy.
(ii) Similarly, the scandide contraction causes gallium to have a higher ionization energy than aluminum due to a similar increase in effective nuclear charge, making electrons harder to remove.