The effective nuclear charge, Zeff, for a valence electron can be approximated using the core charge of the atom, that is, the total charge Z of the nucleus and the inner (nonvalence) electrons. Determine the core charge for an atom of Al.
The Correct Answer and Explanation is:
The core charge for an atom is calculated by determining the effective nuclear charge experienced by an electron in the valence shell, which is influenced by the total number of protons in the nucleus (atomic number, Z) and the shielding effect from the inner electrons.
For an atom of aluminum (Al):
- Atomic number (Z): The atomic number of aluminum is 13, which means it has 13 protons in the nucleus.
- Electron Configuration: The electron configuration of aluminum is 1s22s22p63s21s^2 2s^2 2p^6 3s^21s22s22p63s2. The first two energy levels (1s, 2s, and 2p) are filled with electrons, while the outermost shell (3s) contains the valence electrons.
- Core Electrons: These are the electrons in the inner shells that do not participate in bonding or chemical reactions. For aluminum, the core electrons are the electrons in the 1s21s^21s2, 2s22s^22s2, and 2p62p^62p6 orbitals. This gives a total of 10 core electrons.
- Valence Electrons: The valence electrons are the electrons in the outermost shell, which is the 3s23s^23s2 orbital in this case. Aluminum has 3 valence electrons.
- Core Charge (Zeff): The core charge is calculated by subtracting the number of core electrons from the total atomic number. This represents the effective nuclear charge felt by the valence electrons due to the shielding from the inner electrons. Core Charge(Zeff)=Z−core electrons=13−10=3\text{Core Charge} (Z_{\text{eff}}) = Z – \text{core electrons} = 13 – 10 = 3Core Charge(Zeff)=Z−core electrons=13−10=3
Thus, the effective nuclear charge for the valence electrons in an aluminum atom is 3. This means that the valence electrons experience a net charge of +3 from the nucleus after accounting for the shielding effect of the 10 inner electrons. This value influences the chemical behavior and reactivity of aluminum, as it governs the attraction between the nucleus and the valence electrons.
