How are diatomic molecules formed?

Why do some atoms bind with other atoms of their own elements, such as O2 and N2, and why do others not? What property of these atoms enable them to do this?
 
Are you asking about covalent bonds exclusively? The short answer is that "a full octet is more stable, so they share their electrons", but this does not cover the atoms that no not form covalent dimers, like Be. The long answer involves what are called binding and antibinding molecular orbitals. I advice you to consult any first year university chemistry textbook for an introduction to this topic.
 

alxm

Science Advisor
1,841
7
this does not cover the atoms that no not form covalent dimers, like Be.
Ah, but Beryllium http://www.sciencemag.org/content/324/5934/1548.abstract" [Broken] form a covalent dimer! Or perhaps I should say 'covalent-ish'; there really isn't a word for that peculiar bond, although it's certainly stronger than can be accounted for by 'proper' dispersion forces (which is what most theory would predict to be the only bonding force). You could say the bond is too weak to be covalent and too short to be dispersion.

It's a noteworthy failure of all the simple bonding theories (MO, VB, Lewis).
 
Last edited by a moderator:
Wow, thanks for that interesting read! :biggrin:

Judging by the references provided, all the earth alkali metals actually form dimers! My first "instinct" is that the error of the standard bonding models arise because they don't take into account the effect of both nuclei on the electron wavefunctions. Is that the case?
 

DrDu

Science Advisor
5,982
728
No, the nuclei aren't important. The binding in Be_2 etc. is so complicated due to strong correlation of the electrons.
 
No, the nuclei aren't important. The binding in Be_2 etc. is so complicated due to strong correlation of the electrons.
I still don't see how they form. I mean I know Alkaline metals are reactive, but Nitrogen and Oxygen due this. Why dont other elements? And both ionic and covalent bonds.
 

DrDu

Science Advisor
5,982
728
I don't see the basis for your question. In gas phase, homonuclear diatomic molecules of practically all elements have been observed. With the exception of the bonding between noble gasses, these bonds are considerably stronger than van der Waals bonds, i.e. they are really covalent bonds. The classic reference is G. Herzberg, Molecular Spectra and Molecular Structure: Spectra of Diatomic Molecules
 

Borek

Mentor
27,999
2,509
If I understand correctly what is LogicalAcid current level of education, diatomics other than those most basic (H2, N2, O2 and halogens) are too esoteric to be not confusing.

It is all in energy - those commonly observed have much lover energy than atomic gases, so they dominate in conditions that we assume standard (around 1 atm and around room temperature). Those exotic ones have lower energy too, but the difference is very small, so they can survive only in gas phase and at low pressures, as in the presence of other elements they have many other ways of getting to the lowest energy state.
 
Last edited:

DrDu

Science Advisor
5,982
728
You are probably right Borek, nevertheless then I do not quite understand what the question is. Maybe that not for all elements the diatomic molecules are the most stable ones in comparison with other struktures? I think LocigalAcid could precise that point.
 
You are probably right Borek, nevertheless then I do not quite understand what the question is. Maybe that not for all elements the diatomic molecules are the most stable ones in comparison with other struktures? I think LocigalAcid could precise that point.
Basically, why do some elements form diatomic molecules and others not?
 

DrDu

Science Advisor
5,982
728
Tell me an element besides the noble gasses which does not form a diatomic molecule.
 

DrDu

Science Advisor
5,982
728
It does.
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top