Final answer:
For aluminum (Al), the shielding constant (S) for the valence electron is approximated by the number of non-valence electrons, which is 10 (accounting for the 1s², 2s², and 2p⁶ electrons).
Step-by-step explanation:
To calculate the shielding constant (S) for the valence electron of aluminum (Al), we need to consider the number of non-valence electrons that shield the valence electron from the nucleus. Aluminum has an electron configuration of [Ne]3s²3p¹, meaning it has a total of 13 electrons. The inner electrons (1s², 2s², and 2p⁶) shield the valence electrons in the 3s² and 3p¹ orbitals. Since there are 10 electrons in the 1s, 2s, and 2p orbitals, these are the non-valence electrons providing the shielding.
Therefore, for the last valence electron in the 3p orbital, the shielding constant S is approximately equal to the number of non-valence electrons (1s², 2s², 2p⁶), which is 10. This estimation would give us the nearest whole number for the shielding constant, which could then be further refined with more sophisticated models if necessary.