The unpaired electrons in Al and Si are present in 3p orbital. Which electrons will experience more effective nuclear charge from the nucleus

To understand which electrons experience a greater effective nuclear charge between aluminum (Al) and silicon (Si), we need to delve into the concepts of electron configuration and effective nuclear charge. Both elements have unpaired electrons in their outermost p orbitals, but the way these electrons interact with the nucleus differs due to their atomic structure.

Electron Configuration Overview

Aluminum has the atomic number 13, and its electron configuration is 1s² 2s² 2p⁶ 3s² 3p¹. Silicon, on the other hand, has the atomic number 14, with the electron configuration of 1s² 2s² 2p⁶ 3s² 3p². The key point here is that both elements have their outermost electrons in the 3p orbital, but the number of protons in the nucleus differs: Al has 13 protons, while Si has 14.

Understanding Effective Nuclear Charge

The effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the actual nuclear charge (the number of protons) and the shielding effect caused by inner electrons. The formula to estimate Z_eff is:

• Z_eff = Z - S

Where Z is the atomic number and S is the shielding constant, which represents the extent to which inner electrons shield outer electrons from the nucleus.

Comparing Aluminum and Silicon

In aluminum, the unpaired electron in the 3p orbital experiences a nuclear charge of +13 from the nucleus. However, it is shielded by the 10 inner electrons (1s² 2s² 2p⁶), leading to a significant shielding effect. This results in a lower effective nuclear charge for the 3p electron in Al.

For silicon, the unpaired electrons in the 3p orbital feel a nuclear charge of +14. Although it is also shielded by the same 10 inner electrons, the additional proton in silicon's nucleus means that the effective nuclear charge is higher than that experienced by the unpaired electron in aluminum.

Conclusion: Which Experiences More Effective Nuclear Charge?

To summarize, the unpaired electrons in silicon experience a greater effective nuclear charge compared to those in aluminum. This is primarily due to the higher number of protons in silicon's nucleus, which increases the attractive force on the outer electrons despite the similar shielding effect from the inner electrons. Therefore, the unpaired electrons in Si are held more tightly by the nucleus than those in Al.

This concept is crucial in understanding the chemical behavior of these elements, as a higher effective nuclear charge can influence properties such as ionization energy and electronegativity.