Assertion (A): The valence shell electronic configuration of Cr is 4s'3d.
Reason (R) : To attain stability, one electron from 4s orbital is shifted to 3d orbital.
Answers
Answer:
assertion is wrong. Reason can be correct but gnerally Cr forms +3 oxidising state more stabl
Explanation:
Cr= [Ar] 3d^5 4s^1
Chromium has ground state configuration of [Ar]3d
5
4s
1
after it has attained a configuration of +3 its electronic configuration becomes [Ar]3d
3
this makes it half filled stable at the t
2g
level which means three sub-D orbitals i.e. dxy dyz dxz are half filled.
Half filled t
2g
state is more stable than d
5
configuration so ,Chromium is more stable in its d
3
state than its d
5
state.
Hence chromium is more stable in +3 oxidation
Answer:-
Both Assertion and Reason are correct.
Chromium (Cr) has configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵ instead of 4s² 3d⁶ because it is a half stabled element , and 1 electron from 4s is moved to 3d orbital to attain stability.
Copper (Cu) is an other example for this type of elements. It has the configuration of 4s¹ 3d¹⁰ instead of 4s² 3d⁹.
Generally these elements do not follow the Aufbau's Principle since the electrons are arranged half filled in the orbitals.
Hence, we can say that both Assertion and Reason are correct.