Question

Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.

Answer 1

(a) Phosphorus (P):   Atomic number = 15 
(b) Silicon (Si): Atomic number = 14 
(c) Chromium (Cr): Atomic number = 24 
(d) Iron (Fe): Atomic number = 26 
(e) Krypton (Kr): Atomic number = 36 .

Answer 2

(a) Phosphorus (P): 1s2 2s2 2p6 3s2 3p3

No of unpaired electron = 3

 

(b) Silicon (Si): 1s2 2s2 2p6 3s2 3p2

No of the unpaired electron will be 2 (since p orbital can have highest six atoms)

 

(c) Chromium (Cr): 1s2 2s2 2p6 3s2 3p6 4s1 3d5

No of the unpaired particles will be 6 (since 1 electron is to be added to 4s & 5 electrons to be attached to 3d orbital.

 

(d) Iron (Fe): 1s2 2s2 2p6 3s2 3p6 4s2 3d6

No of unpaired electrons = 4

 

(e) Krypton (Kr): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Therefore, all orbitals are fully occupied, which means there are no unpaired electrons in krypton.