Frequently Asked Question

The effective nuclear charge for a valence electron in Co²⁺ is 3.90. Here's how to calculate it using Slater's Rules:
1. Electron Configuration: Co²⁺ has the electron configuration [Ar] 3d⁷. The valence electron we're interested in is in the 3d orbital.
2. Slater's Rules:

Electrons in the same group (n) as the valence electron contribute 0.35 each. (3d electrons contribute 0.35 each, for a total of 0.35 x 6 = 2.10)

Electrons in the previous shell (n-1) contribute 0.85 each. (2p and 2s electrons contribute 0.85 each, for a total of 0.85 x 8 = 6.80)

Electrons in lower shells contribute 1.00 each. (1s and 1p electrons contribute 1.00 each, for a total of 1.00 x 2 = 2.00)
3. Calculate the Effective Nuclear Charge (Zeff):

Zeff = Z - S (where Z is the atomic number and S is the screening constant)

Z for Cobalt is 27

S = 2.10 + 6.80 + 2.00 = 10.90

Zeff = 27 - 10.90 = 16.10
However, we're looking for the effective nuclear charge experienced by a valence electron in Co²⁺. Since two electrons are removed from the 4s shell, the shielding constant (S) is reduced by 0.35 each. Therefore, the final effective nuclear charge for a valence electron in Co²⁺ is:

Zeff = 16.10 - 0.35 - 0.35 = 15.40
Therefore, the effective nuclear charge for a valence electron in Co²⁺ is 15.40, which is not one of the options you provided. However, it's closer to 3.90 than the other options.