The effective nuclear charge (Zeff) experienced by the 4s electrons in zinc (Zn) is approximately 4.35.
While the actual nuclear charge of zinc is +30 (due to 30 protons in its nucleus), the inner electrons shield the outer 4s electrons from the full force of this charge. This shielding effect reduces the attraction experienced by the 4s electrons, resulting in a lower effective nuclear charge.
Here's a breakdown of why this is the case:
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Nuclear Charge (Z): Zinc has an atomic number of 30, meaning it has 30 protons in its nucleus. Therefore, Z = +30.
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Shielding Effect: The inner electrons (1s, 2s, 2p, 3s, 3p, 3d) effectively "shield" the outer 4s electrons from the full positive charge of the nucleus. These inner electrons repel the outer electrons, counteracting some of the nuclear attraction.
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Effective Nuclear Charge (Zeff): The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It is calculated as:
- Zeff = Z - S
Where:
- Z is the actual nuclear charge (atomic number).
- S is the shielding constant, representing the shielding effect of the inner electrons.
Different methods can be used to estimate the shielding constant (S), leading to slightly varying Zeff values. However, a commonly cited value for the Zeff experienced by the 4s electrons in zinc is approximately 4.35. This indicates that the 4s electrons effectively "see" a positive charge of only +4.35, rather than the full +30.
