Molecular covalent bonds across energy levels

In summary, the conversation touches on the topic of valence electrons and their role in forming bonds. The group discusses how the inclusion of full inner electrons does not contribute to overall bonding, and only the outermost electrons are likely to show any net bonding. They also mention the use of simple examples for demonstration purposes and the difficulty in drawing orbitals for elements with d orbitals. The concept of electronegativity and its relation to ionic bonds is also brought up, with a reference to Koopman's theorem.
  • #1
nomadreid
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In examples for molecular covalent bonds on the Internet (e.g., the site given in the full text), all components, with the exception of hydrogen, have the same energy level n. Yet there are bonds formed from orbitals of different energy levels, even though the bonding is more likely for identical n, no? So isn't it just whether the orbitals are s's, p's, an sp hybrid, or whatever? Why the n?
I am sure this is an elementary question; I'm just trying to clarify some points that were poorly explained to me years ago in secondary school. I know that a full answer would involve solving Schrödinger's equation etc., but keeping this on the level of valence electrons,...) I was confused by the sites, e.g. , https://chem.libretexts.org/Bookshe...1.7:_Molecular_Orbitals_and__Covalent_Bonding, using only components , besides H, that had the same n for all components. After all, isn't the whole idea of a group the similarities across peiods?
 
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  • #2
I think it is a case of giving you the simplest possible examples, using only the outermost electrons, where n, the principle quantum number, is the main contribution to the energy of the outer electrons, and l the azimuthal quantum number making a smaller contribution to the energy of the orbitals. They are deliberately choosing elements with only s and p orbitals to keep it simple but still show that predictions can be made.

If the full inner electrons were included, they would show that the number of bonding and antibonding orbitals would be the same, all would be full, and so make no contribution to the overall bonds as the bonding orbitals are canceled by the antibonding orbitals. It's only the outermost orbitals, when they are not full, that are likely in their examples to show any overall net bonding.

You could draw them all out for the sodium example and see this for yourself. Then repeat for potassium, and as the diagram becomes bigger you will see why they ignore the ones which don't contribute overall to the bonding.

And when it gets to elements with d orbitals, it gets even harder to draw.
 
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  • #3
Thanks, @DrJohn. The reason for not including the inner electrons is clear, but I thought it would be even simpler if, instead of saying for example, ns1 and ns1 give nσ, say that, among the valence electrons, ns1 and ms1 give σ, or something similar. But your explanation that that they are simply using the simplest examples makes sense, though. It just worried me to think that I was missing something...
 
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  • #5
caz, thanks. Looks good. downloaded!
 
  • #6
If the orbitals are of vastly different energy, you'd rather get an ionic bond.
 
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  • #7
Thanks, DrDu. I never noticed that. Very helpful!
 
  • #8
You are welcome!
This reasoning can be formalized. Pauling already introduced the electronegativity, which determines the ionicity of the bonds, in terms of the electron affinity and ionization energy.
According to Koopman's theorem, both are given basically in terms of the LUMO and HOMO orbital energies. https://en.wikipedia.org/wiki/Koopmans'_theorem
 
  • #9
DrDu, thanks again; once again, your comments are helpful and the Wiki article is as well.
 

1. What is a molecular covalent bond?

A molecular covalent bond is a type of chemical bond formed between two or more atoms through the sharing of electrons. This type of bond is typically found in nonmetallic elements and results in the formation of molecules.

2. How does a covalent bond form across energy levels?

A covalent bond forms across energy levels when the electrons of two atoms are attracted to the positively charged nuclei of each other. The electrons are shared between the atoms, resulting in a more stable configuration and the formation of a covalent bond.

3. What determines the strength of a covalent bond?

The strength of a covalent bond is determined by the number of shared electrons between the atoms and the distance between the nuclei of the atoms. The more shared electrons and the shorter the distance between the nuclei, the stronger the bond will be.

4. How does the energy level of an atom affect covalent bonding?

The energy level of an atom affects covalent bonding by determining the number of electrons available for bonding. Atoms with higher energy levels have more electrons available for bonding, making them more likely to form covalent bonds with other atoms.

5. What are the properties of molecules with strong covalent bonds?

Molecules with strong covalent bonds tend to be more stable and have higher melting and boiling points. They also tend to be less reactive and have a higher degree of hardness and strength. Examples of molecules with strong covalent bonds include diamond, water, and carbon dioxide.

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