# Orbital Shielding

1. Feb 8, 2015

### henry3369

Assuming all orbitals are filled, which of these orbitals is most shielded: 1s, 3s, 4d, 5s

The answer is 4d, but I chose 5s. Can someone explain? I thought the electrons in the d block are considered core electrons and contribute to the shielding, but feel more pull from the nucleus because of this and the 5s orbital is higher in energy and the electrons are valence electrons so they experience the most amount of shielding. Isn't this why electrons are removed from the 5s block before the 4d because the 5s orbital have more energy?

2. Feb 8, 2015

### Simon Bridge

It's kinda a trick question: the 5s/4d orbitals reverse the usual sequence of s after d.
The 5s orbitals are (usually) filled before the 4d, s the 4d orbitals get more shielding.
s shells are spherical, too, so that makes them better at shielding.

3. Feb 9, 2015

### DrDu

With "assuming all orbitals to be filled" I suppose you mean 1s22s22p63s23p63d104s24p64d105s2?

Then applying these rules, the 5s electron sees an effective charge of 4.35 while the 4d a charge of 8.85. So clearly, the 5s is more strongly shielded than 4d.

Last edited: Feb 9, 2015
4. Feb 9, 2015

### cgk

I'd just like to add that the energy argument can be highly misleading when estimating the shielding. Even when the 4d orbitals would represent comparable energy levels to the 5s orbitals, the 4d orbitals would still be much more compact (i.e., smaller in space) and represent d orbitals, which are less strongly shielded in any case. So, as DrDu said, I'd find it hard to believe that the 4d are more strongly shielded than the 5s.

5. Feb 9, 2015