The effective nuclear charge,Z fff
, for a valence electron can be approximated using the core charge of the atom; that is, the total charge of the nucleus and the inner (nonvalence) electrons. Determine the core charge for an atom of Si. Incorrect -1
The Correct Answer and Explanation is:
To determine the core charge for an atom of silicon (Si), we need to first understand the concept of effective nuclear charge and core charge.
Core charge is the effective positive charge that is “felt” by the valence electrons in an atom. This is calculated by subtracting the number of shielding electrons (non-valence electrons) from the total nuclear charge (the number of protons).
Step-by-Step Process:
- Identify the atomic number of Si:
Silicon (Si) has an atomic number of 14, meaning it has 14 protons in its nucleus. - Electron Configuration:
The electron configuration of silicon is: 1s22s22p63s23p21s^2 2s^2 2p^6 3s^2 3p^21s22s22p63s23p2 This means silicon has 14 electrons in total. The first 10 electrons (in the 1s, 2s, and 2p orbitals) are core electrons, and the remaining 4 electrons (in the 3s and 3p orbitals) are valence electrons. - Calculate the core charge:
The core charge is approximately the nuclear charge (Z) minus the number of shielding electrons. In this case, the core electrons are those in the 1s, 2s, and 2p orbitals. There are 10 core electrons that shield the valence electrons from the full effect of the nuclear charge. The core charge for silicon is: Core Charge=Z−Number of core electrons=14−10=+4\text{Core Charge} = Z – \text{Number of core electrons} = 14 – 10 = +4Core Charge=Z−Number of core electrons=14−10=+4
Therefore, the core charge for silicon (Si) is +4.
Explanation:
The core charge represents the net positive charge that the valence electrons “feel” after accounting for the shielding effects of the inner electrons. For silicon, with its electron configuration, the valence electrons experience a +4 charge from the nucleus due to the shielding by the inner electrons.
Why -1 is Incorrect:
A core charge of -1 would imply that the silicon atom has more electrons than protons, which is not the case for neutral silicon. Silicon has 14 protons and 14 electrons, so the core charge should be positive. The shielding by 10 core electrons reduces the effective nuclear charge felt by the 4 valence electrons, but it does not result in a negative core charge.
