-4

How do boron atoms make five bonds with other boron atoms even if the electron configuration of unbound boron atoms is [He]2s²2p¹, i.e. there is an insufficient number of outer electrons? Are the inner electrons ([He]) involved in binding?

enter image description here

$\ce{B12H12^2-}$, source: https://commons.wikimedia.org/wiki/File:Dodecaborate(12)-dianion-from-xtal-3D-bs-17.png

Karsten
  • 40,170
  • 8
  • 67
  • 183
Get_ Maths
  • 127
  • 5
  • 4
    Even though you've completely rewritten the question, it's still cryptic. Boron-12 refers to an isotope $\ce{^{12}B},$ but I think you are asking about the $\ce{B12}$ icosahedra of either a standalone cluster, or a certain allotrope (which one?). Also, what "stable core" are you asking about? I suspect this could be a duplicate of https://chemistry.stackexchange.com/questions/32319, but I'm not sure I fully understand the question. – andselisk Feb 03 '22 at 06:22
  • 3
    Be aware that laconic, not elaborated questions are usually closed on the StackExchange network. How do I ask a good question?. Describe the question well, search, think, refer and summarize. Well elaborated questions have higher probability to receive acceptable answers. Lack of explicit, a priori effort may cause missing existing answers, question misinterpretation, needed clarification and difficult estimation of the OP knowledge . – Poutnik Feb 03 '22 at 08:47
  • 2
    The short answer is that a bond can cover multiple linkages, not just a single pair of atoms; therefore an atom can be joined to more neighbors than the number of bonds it forms. When you learn about molecular orbitals you can see how this happens. – Oscar Lanzi Feb 03 '22 at 11:55
  • @andselisk I am talking of dodecahedron structure of boron-12 and not of isotopes . – Get_ Maths Feb 04 '22 at 04:26
  • 3
    @Get_Maths You've probably misread my comment. "Boron-12" is a notation for isotope that is equivalent to $\ce{^{12}B}.$ In the context of recent edit, you should refer to your composition as to dodecaborate, not boron-12 since the latter causes confusion. – andselisk Feb 04 '22 at 04:52

1 Answers1

5

Boron makes not five but six bonds in compounds such as dodecaborate or boron carbide. Boron carbide is a semiconductor, so it has aspects of a metal and a non-metal. For actual metals such a elemental sodium, you have to explain twelve nearest neighbors with only 1 outer electron, so there is no way to describe it with covalent bonds. For boron carbide, you can get away with invoking 3 center 2 electron bonds, but it is not clear if there is much insight to be gained.

Roald Hoffmann wrote a detailed account of bonding in boron carbide here. Even if all you get out of it is that boron makes beautiful intricate structures, and 2 electron bonds do not do justice to all compounds known, it is worthwhile taking a look.

enter image description here

I don't think any of the bonding models make use of the inner electrons.

Karsten
  • 40,170
  • 8
  • 67
  • 183
  • But if boron's maximum covalency is 4 , then how can it make 6 bonds – Get_ Maths Feb 04 '22 at 18:24
  • 2
    Call it advanced inorganic chemistry. Either you need less than 2 electrons per bond, or a bond connects more than two atoms. The existence and structure of the boron icosahedra is well supported by experiment. If your bonding model cannot explain it, you need a more sophisticated bonding model. – Karsten Feb 04 '22 at 18:30