CBSE Class 11-science Answered

Effective nuclear charge is the net positive force experienced by electron inside an atom.

Atomic number of Scandium = Z = 21

E.C. of Scandium = (1s²)(2s²2p²)(3s²3p²)(3d¹)(4s²)

Effective nuclear charge = Zeff for 4s electron in scandium = Z – S

Where S is shielding effect.

According to Slater’s rule,

S is 0.35 per electron for n orbital

S is 0.85 per electron for n-1 orbital

S is 1 per electron for n-2 and so on orbital

In Scandium,

n = 4s = 1 electron 

n-1 = 3s²3p⁶3d¹ = 9 electrons

n-2 = 2s²p⁶ = 8 electrons

n-3= 1s² = 2 electrons

Therefore,

S= (1×10) + (0.85×9) + ( 0.35 × 1)= 0.35 + 7.65 + 10 = 18

Hence, Zeff for 4s electron of Scandium =  Z−S =  21 – 18 = 3