Question

successive members of the first row
transition elements are listed below with
their atomic numbers. Which one of them is
expected to have the highest third ionization
enthalpy :


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Answer 1

$\displaystyle\underline{\bigstar\orange{\sf Question}}$

• Four successive members of the first row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy :-

(1) Vanadium (Z = 23)

(2) Manganese (Z = 25)

(3) Chromium (Z = 24)

(4) Iron (Z = 26)

$\displaystyle\underline{\bigstar\pink{\sf Answer}}$

• ✭ Manganese has the highest ionisation enthalpy.

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• »» Generally across the period , ionisation energy increases except some places.
• Half filled and completely filled orbital requires more energy to remove the electron from its orbit. Hence they have high ionisation energy.

• »» Half filled d orbital has 5 electrons. It confers maximum stability.

• ➳ Vanadium electronic configuration is 3d³ 4s².
• ➳ Chromium electronic configuration is 3d⁵ 4s¹
• ➳ Manganese electronic configuration is 3d⁵ 4s²
• ➳ Iron electronic configuration is 3d⁶ 4s².

$\displaystyle\bullet\sf{\:Chromium}$

• »» When it loses an electron from 4s orbital , it stablises by half filled 3d orbital. So it is easy to remove one electron. It has low ionisation enthalpy.

$\displaystyle\bullet\sf{\:Vanadium}$

• »» When it loses an electron from 4s orbital , the configuration becomes 3d³4s¹. It is neither half filled nor completely filled. So ionisation enthalpy is relatively low.

$\displaystyle\bullet\sf{\:Iron}$

• »» The removal of electron from 4s orbital has no dependence on its stability factor . Its ionisation enthalpy is also comparitively low.

$\displaystyle\bullet\sf{\: Manganese}$

• »» It is already in half filled state. So it becomes difficult to remove the electron from its outer orbital. So its ionisation energy is much higher.

• ✪ Expected order of ionisation energy: V<Cr<Mn<Fe

• ✪ Correct order: V<Cr<Fe<Mn

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