Factors affecting Zeff:
* Number of core electrons: The more core electrons there are, the greater the shielding effect, resulting in a lower Zeff.
* Principal quantum number (n) of the valence electron: Electrons in higher energy levels (larger n) experience a weaker Zeff because they are farther from the nucleus and are shielded more effectively by the core electrons.
* Electron configuration: Electrons in subshells with higher azimuthal quantum number (l) are shielded more effectively, resulting in a lower Zeff.
Calculation of Zeff:
Zeff can be estimated using Slater's rules, which provide a set of empirical constants to account for the shielding effect.
Consequences of Zeff:
* Atomic radius: Higher Zeff leads to a smaller atomic radius as the valence electrons are pulled closer to the nucleus.
* Ionization energy: Higher Zeff leads to a higher ionization energy as it requires more energy to remove a valence electron.
* Electronegativity: Higher Zeff leads to higher electronegativity as the atom has a stronger attraction for electrons.
* Chemical reactivity: Zeff plays a significant role in determining the chemical reactivity of an element.
Example:
Consider sodium (Na), which has 11 protons (Z = 11) and an electronic configuration of 1s²2s²2p⁶3s¹. The valence electron in the 3s orbital experiences a Zeff of approximately +1, due to the shielding effect of the 10 core electrons.
In summary, the effective nuclear charge experienced by valence electrons is a key factor influencing various atomic and chemical properties.
