Why does Cr have a higher melting point than Mn?

Question

Read the following passage and answer the next five questions based on it.
The transition metals are very hard and have low volatility. Their melting and boiling points are high. In any row, the melting points of these metals rise to a maximum at d5 and fall regularly as atomic number increases. The high melting points of these metals are attributed to the involvement of greater number of electrons from (n– 1)d in addition to ns electrons in the interatomic metallic bonding.

Answer 1

Step 1: Link melting point to bonding.
The melting point of a transition metal depends on how strong its metallic bonding is, which depends on the number of unpaired electrons taking part in bonding.

Step 2: Write the configurations.
Chromium is \([Ar]3d^5 4s^1\), giving six unpaired electrons available for bonding. Manganese is \([Ar]3d^5 4s^2\), where the \(4s\) electrons are paired, so effectively five unpaired electrons are available.

Step 3: Compare the bonding electrons.
Chromium has more unpaired electrons free for metallic bonding than manganese.

Step 4: Relate to bond strength.
More unpaired electrons make stronger metallic bonds, which need more energy to break.

Step 5: Conclude.
So chromium has stronger metallic bonding and a higher melting point than manganese.

Answer: Chromium \((3d^5 4s^1)\) has more unpaired electrons taking part in metallic bonding than manganese \((3d^5 4s^2)\), so its metallic bonds are stronger and its melting point is higher.

List-I	Transition metal/compound
A	V₂O₅
B	Fe
C	PdCl₂
D	Ni complex

List-II	Catalytic role
I	Preparation of ammonia from N₂/H₂ mixture
II	Polymerisation of alkynes
III	Oxidation of SO₂ to SO₃
IV	Preparation of ethyne to ethene

Why does Cr have a higher melting point than Mn?

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Solution and Explanation

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