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Calculez la masse moléculaire d'un composé.
Charge nucléaire effective (Z_eff)
2.20
Effective Nuclear Charge (Z_eff) vs Atomic Number (Z)
Formule
Effective Nuclear Charge
Formula
Z_eff = Z − σ
Where:
Inner electrons shield outer electrons from the full nuclear charge. Z_eff increases across a period (more protons, similar shielding) and stays roughly constant down a group.
Exemple Résolu
Sodium (Z = 11) with shielding constant σ = 8.8 for the 3s electron.
- 01Z_eff = Z - σ
- 02Z_eff = 11 - 8.8
- 03Z_eff = 2.2
- 04The 3s electron feels an effective charge of +2.2
Questions Fréquentes
What is effective nuclear charge?
Z_eff is the net positive charge experienced by an electron after accounting for shielding by inner electrons. It determines how tightly the electron is held.
What are Slater's rules?
Slater's rules provide a systematic way to estimate the shielding constant σ. Different electron groups contribute different amounts of shielding.
Why does Z_eff matter?
Z_eff explains periodic trends in atomic radius, ionization energy, and electronegativity. Higher Z_eff pulls electrons closer and makes them harder to remove.
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