What is the electron configuration for Gd?

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Discussion Overview

The discussion revolves around the electron configuration of gadolinium (Gd), focusing on the correct arrangement of electrons in its atomic orbitals. Participants explore the implications of half-filled orbitals and the energy levels of 4f and 5d orbitals, with a particular emphasis on why Gd's configuration may deviate from expected patterns.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes the electron configuration [Xe]6s²4f⁸ but questions its correctness based on a hint that suggests the last two orbitals are only half full.
  • Another participant suggests an alternative configuration of [Xe]6s²4f⁷5d¹, explaining that 4f and 5d orbitals are close in energy, leading to stability considerations for half-filled orbitals.
  • There is a query about whether Gd is an exception to the general filling order of orbitals and how one can determine when a configuration is energetically favorable.
  • A later reply confirms that Gd is indeed an exception and suggests that memorization of such exceptions is necessary, noting that there are few exceptions to the general rules of electron configuration.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the electron configuration of Gd, with multiple competing views on the stability of half-filled orbitals and the filling order of orbitals. The discussion remains unresolved as participants explore different perspectives without reaching a consensus.

Contextual Notes

Participants highlight the complexity of orbital energy levels and the exceptions to typical filling orders, indicating that the discussion may depend on specific definitions and interpretations of stability in electron configurations.

jumbogala
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Homework Statement


What is the electron configuration for Gd?

Homework Equations


None


The Attempt at a Solution


Since Gd has 64 electrons, I would assume that the electron config. is:

[Xe]6s24f8

Apparently this is wrong. The hint the question gives is that the last two orbitals are only half full... so I guess it would be something like:

[Xe]6s24f75d1

But why? According to my diagram, the 4f level fills up before the 5d level does, so why wouldn't it take all 14 spaces for the electrons?

And if the 4f level doesn't really fill up before the 5d level, then why do lower levels fill up in weird orders like (1s2,2s2,2p6,3s2). Eg. Why does it jump from s to p then back to s?
 
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jumbogala said:
[Xe]6s24f75d1

But why? According to my diagram, the 4f level fills up before the 5d level does, so why wouldn't it take all 14 spaces for the electrons?

4f and 5d are very close in terms of energy levels. In such case strange things may happen. Half filled orbital is slightly more stable than orbital with one additional electron. You put 7 electrons on 4f and when you add next electron it may land on 4f - but then you loose half orbital premioum - or on 5d. It happens that the latter version is energetically better.

And if the 4f level doesn't really fill up before the 5d level, then why do lower levels fill up in weird orders like (1s2,2s2,2p6,3s2). Eg. Why does it jump from s to p then back to s?

It is all about orbital energy level.
 
So is Gd an exception to the rule, then? How do I know then something is energetically better?
 
jumbogala said:
So is Gd an exception to the rule, then? How do I know then something is energetically better?

It is exception, and honestly, the only way to know these expception is to remember them. There are a few of them, less then five if I recall correctly. Any reasonably good general chemistry book should list them in the electron configuration section.
 

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