Chromium is a first-row transition element with an atomic number of 24. During a chemical … — JAMB UTME

Chromium is a first-row transition element with an atomic number of 24. During a chemical reaction, a neutral chromium atom loses three electrons to form the chromium(III) cation, $Cr^{3+}$ . Which electronic structure correctly represents this $Cr^{3+}$ ion in its ground state?

$[Ar] 3d^3$ Answer
B
$[Ar] 3d^1 4s^2$
C
$[Ar] 3d^2 4s^1$
D
$[Ar] 3d^4$

Answer

The ground-state electronic configuration of the chromium(III) ion,

Cr^{3+}

, is

[Ar] 3d^3

Neutral chromium has an electronic configuration of

[Ar] 3d^5 4s^1

due to half-filled subshell stability. When forming a

Cr^{3+}

cation, the atom loses three electrons: the single valence electron in the

4s

orbital is lost first, followed by two electrons from the

3d

subshell, leaving a final ground-state configuration of

[Ar] 3d^3

Step-by-Step Solution

Determine the ground-state electronic configuration of neutral chromium (

Cr

Z = 24

Neutral chromium has the anomalous configuration

[Ar] 3d^5 4s^1

Chromium exhibits an exception to the standard Aufbau principle because a half-filled

d

-subshell (

3d^5

) provides extra thermodynamic stability.

Apply the rule for cation formation in transition metals.

Electrons in the outermost principal quantum shell (

4s

) are removed prior to removing electrons from the inner

(n-1)d

subshell (

3d

Once filled, the

3d

orbitals experience greater nuclear attraction and drop lower in energy than the

4s

orbital.

Deduct three electrons to account for the

+3

charge of

Cr^{3+}

Remove the single electron from

4s

(

[Ar] 3d^5 4s^0

), then remove two electrons from

3d

to obtain

[Ar] 3d^3

Removing 3 electrons total converts neutral

Cr

into

Cr^{3+}

Key Concept

Electronic Configuration of Transition Metal Cations

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic