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

[scott_alexsk]

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

 

[ZapperZ]

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.

 

[scott_alexsk]

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

 

[ZapperZ]

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.