Question

Why chromium is placed in the d block in the Periodic Table.

Answer 1

Answer:

The d-Block consists of three series in Periods 4, 5, and 6. Each series contains ten elements.

In the ground state of an atom, the electrons are always arranged to give the lowest energy value.

Electrons repel each other (both have negative charge), so a lower energy is achieved by placing the electrons singly in orbitals than if they are paired.

The energies of 3d and 4s orbitals are very close together in period four. It works out that with chromium and copper, putting the two electrons in the 4s orbital would result in a higher energy, thus they fill the 3d orbital first.

Explanation:

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Answer 2

D-BLOCK

• The elements in the d-block have completely filled d-shell.
• Due to the special electronic configuration of the elements, they show different characteristic properties.
• Chromium has an electronic configuration of $3d^54s^1.$

• The element has extra stability due to the presence of a half-filled d-shell.
• The electrons are always arranged in the lowest energy shell so, in-ground state, electrons should go first in 4s than 3d due to the lowest energy of the 4s shell.
• Despite the low energy of 4s, electrons are arranged in 3d orbitals to attain a stable electronic configuration of much lower energy than 4s.