MO for heteronuclear diatomic molecules? Watch

thenextchemist
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How do we know which molecular orbital diagram to draw for heteronuclear diatomic molecules?

Like, for homonuclear diatomic molecules, between lithium and nitrogen, the sigma orbital is higher in energy than the pii orbitals.
And vice versa for atoms between oxygen and fluorine.

However, what about molecules such as BO, CO and NO?

Which molecular orbital diagram do we follow?

Thank you


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shengoc
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(Original post by Bloom77)
How do we know which molecular orbital diagram to draw for heteronuclear diatomic molecules?

Like, for homonuclear diatomic molecules, between lithium and nitrogen, the sigma orbital is higher in energy than the pii orbitals.
And vice versa for atoms between oxygen and fluorine.

However, what about molecules such as BO, CO and NO?

Which molecular orbital diagram do we follow?

Thank you


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The more electronegative atom would have more tightly held atomic orbitls hence "lower" in energy reltive to those from less EN atom.

Google "moleculr orbitl of xx" images and check out. sensible textbook on intro to these things usually cover these too.
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thenextchemist
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(Original post by shengoc)
The more electronegative atom would have more tightly held atomic orbitls hence "lower" in energy reltive to those from less EN atom.

Google "moleculr orbitl of xx" images and check out. sensible textbook on intro to these things usually cover these too.
This isn't the case for NO


Oxygen is more electronegative

And the sigma orbital comes before the pii orbital



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shengoc
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(Original post by Bloom77)
This isn't the case for NO


Oxygen is more electronegative

And the sigma orbital comes before the pii orbital



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Hi there i am sure you realise that higher level chemistry takes generalisation with pinch of salt.

Though generally it is like this there are always exceptions. it hppens uni professors love to ask on these special cases.

Sorry i have forgotten bout my MOs though...look through shriver nd tkins or any good inorganic books. might help.

If i recall correctly, it was means to an end....NO is a radical. When forming complexes, the polarity seems to be delta negative on N as most nitrosyl complexes form with the N dative bond to metal complexes.(Google nitrosyl complexes)

It is like CO (carbon monoxide) for example, even though oxygen is more electronegative than carbon, but in terms of polarity, the delta negative is on carbon due to the dative covalent bond within the CO (from oxygen towards C). Look up carbonyl complexes for examples.
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MexicanKeith
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(Original post by Bloom77)
How do we know which molecular orbital diagram to draw for heteronuclear diatomic molecules?

Like, for homonuclear diatomic molecules, between lithium and nitrogen, the sigma orbital is higher in energy than the pii orbitals.
And vice versa for atoms between oxygen and fluorine.

However, what about molecules such as BO, CO and NO?

Which molecular orbital diagram do we follow?

Thank you


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sigma and pi orbitals change order because of s-p mixing. As you move to the right across the row (Li--->F) the energy gap between s and p orbitals gets larger (because the effective nuclear charge increases). It just so happens that the crossover between the orbitals energies happens between N2 and O2. CO is isoelectronic with N2 , its MO diagram is asymmetrical but has the same mixing affects as N2 (ie the sigma and pi are swapped). NO has smaller s p mixing so its MO diagram looks more like O2 (again it will be lopsided because the atoms have different electronegativities!)
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thenextchemist
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(Original post by MexicanKeith)
sigma and pi orbitals change order because of s-p mixing. As you move to the right across the row (Li--->F) the energy gap between s and p orbitals gets larger (because the effective nuclear charge increases). It just so happens that the crossover between the orbitals energies happens between N2 and O2. CO is isoelectronic with N2 , its MO diagram is asymmetrical but has the same mixing affects as N2 (ie the sigma and pi are swapped). NO has smaller s p mixing so its MO diagram looks more like O2 (again it will be lopsided because the atoms have different electronegativities!)
Thank you !!
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