Predicting Crystal Structures in Metals: Is There a Simple Explanation?

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Discussion Overview

The discussion centers on predicting the crystal structures of pure metal elements, exploring the limitations of the 'electron sea' model and considering factors such as valence electrons and orbital types. Participants also inquire about the applicability of these predictions to alloys and precipitation reactions, with a focus on quantum mechanical calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the crystal structure of metals is influenced more by the valence shell of the element rather than the 'electron sea' model.
  • It is suggested that alkali metals tend to adopt a body-centered cubic (BCC) structure due to their fewer valence electrons, while transition metals may form face-centered cubic (FCC) or hexagonal close-packed structures.
  • One participant questions whether the number of closest neighbors required for metallic bonding is related to the number of valence electrons, particularly contrasting alkali and transition metals.
  • There is a discussion about the role of s-orbitals in alkali metals and d-orbitals in transition metals, with a suggestion that the symmetry of these orbitals may influence bonding and structure.
  • Participants inquire if the calculations mentioned can also explain the structures of alloys and precipitation reactions, and whether these calculations are based on quantum mechanics.
  • A participant expresses uncertainty about the applicability of these calculations to alloys and suggests that an expert in the area should contribute further insights.

Areas of Agreement / Disagreement

Participants express differing views on the influence of the 'electron sea' model and the role of valence electrons in determining crystal structures. The discussion remains unresolved regarding the applicability of calculations to alloys and precipitation reactions.

Contextual Notes

There are limitations in the discussion regarding assumptions about bonding and structural preferences, as well as the complexity of calculations involved in predicting crystal structures.

scott_alexsk
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Is there any way to predict what crystal structure a pure metal element will be? It seems that the simple 'electron sea' idea does not explain a lot of things.

Thanks
-scott
 
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scott_alexsk said:
Is there any way to predict what crystal structure a pure metal element will be? It seems that the simple 'electron sea' idea does not explain a lot of things.

Thanks
-scott

Er.. it actually has nothing to do with the 'elecron sea', at least not directly. It has more to do with the valence shell of the element. Alkali metals, for example, tend to have BCC structure, whereas transition metals tend to have either FCC and hexagonal closed pack. But this really is a rather generalized picture. There's a rather complicated, detailed calculations on why such-and-such a structure is more preferred than others. In fact, in some cases, there can even be a structural phase transition at some temperature or pressure.

Zz.
 
So I guess in the case of the alkali metals, since they have fewer valence electrons, they require fewer closest neighbors when forming metallic bonds? For the transition elements, is the same true that since they have a greater number of valence electrons, they require the maximum number of closest neighbors?

Also can these calculations you describe explain the structures of alloys? Can they explain precipitation reactions? Are these calculations based on QM?

Thanks,
-scott
 
scott_alexsk said:
So I guess in the case of the alkali metals, since they have fewer valence electrons, they require fewer closest neighbors when forming metallic bonds? For the transition elements, is the same true that since they have a greater number of valence electrons, they require the maximum number of closest neighbors?

Er.. not quite. Remember that alkali metals have an s-orbital as the valence shell. s-orbitals tend to be isotropic. Somehow, this is conducive to forming BCC structures (don't ask me why). Transition metals have d-orbitals as valence shell. So you expect the symmetry of the d-orbitals to dictate how the covalent or metallic bonds form.

Also can these calculations you describe explain the structures of alloys? Can they explain precipitation reactions? Are these calculations based on QM?

Thanks,
-scott

I don't know. Someone else who is an expert in this area needs to come here and help.

Zz.
 

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