Effective Nuclear Charge

We have already covered the Representation of the s−Orbitals in the previous unit (see below).

Example: 12Mg atom.

Here, we will focus on the effective nuclear charge acting on the outermost electron(s).
Zeff = Z − S Z-eff

Z-Eff 2


So, the question is: How does the trend of Zeff look like in a periodic table ?
Zeff increases as atomic number increases across a period. Z-eff-4

Number of core electrons stays the same, but the actual nuclear charge increases, causing more attraction to the outermost electrons.
The outer-shell electrons added to counterbalance the increasing nuclear charge shield each other ineffectively

Zeff slightly increases as atomic number increases down a group:
Although larger cores are added as we move down a group, these are less able to shield the outer electrons from the nuclear charge.
Z-eff-5 Z-eff-6

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Date of last modification: Summer , 2019