# Quantum mechanical model of an atom

• B
Frigus
We say that principal quantum number tells us the average distance from the nucleus, so the sub shells of some principal quantum number say 3 has 3 sub Shells 0,1,2 and in 3p sub shell their will probability of finding the electron near the nucleus which doesn't mean electron will find in region of 2p orbital.
How can we say that there are different orbitals in an electron as the smaller orbital for example 2p will come in the region of 3p.

## Answers and Replies

Homework Helper
Which part of the calculations are unclear to you ?
Does it worry you that the probability distributions for the distance to the nucleus show overlap ?

Mentor
How can we say that there are different orbitals in an electron as the smaller orbital for example 2p will come in the region of 3p.

Because which orbital the electron is in is not determined by where it is. The electron doesn't even have a definite position to begin with. Which orbital the electron is in is determined by its energy and angular momentum.

Frigus
Please tell me where I am wrong,I think like
That when we say there are two orbitals 1s and 2s and both have spherical shape and the average distance of 2s orbital is larger so doesn't it means that the smaller s orbital will lie in the region of larger s orbital. In my mind their is picture of atom where two orbitals 1s and 2s lie like a ball(of course it is not but it is the region where we can find the electrons) so the the smaller ball region should lie in the volume of smaller if this is the case then both smaller and larger 1s and 2s orbitals share some volume then if we found an electron in the smaller 1s orbital then it is also present in the larger s orbital so then how can we say in which orbital is the electron present and like that their are many numbers of orbitals in an atom doesn't their region overlap with one another.

Frigus
Because which orbital the electron is in is not determined by where it is. The electron doesn't even have a definite position to begin with. Which orbital the electron is in is determined by its energy and angular momentum.
So sir it means that if the election is found near the nucleus then it can be in the larger p orbital but if we find an electron near the nucleus then shouldn't it have less energy than how can we say that it can be in larger 3p orbital as electron energy is less.

Mentor
when we say there are two orbitals 1s and 2s and both have spherical shape and the average distance of 2s orbital is larger so doesn't it means that the smaller s orbital will lie in the region of larger s orbital.

This is not correct. The spatial parts of the wave functions for the orbitals do overlap. Again, which orbital the electron is in is not determined by position. The orbitals are different because they have different combinations of energy and angular momentum, not because they occupy different portions of the space around the nucleus.

if we found an electron in the smaller 1s orbital then it is also present in the larger s orbital

This is not correct. Go back and read what I've already written.

if the election is found near the nucleus then it can be in the larger p orbital

If all we know is the electron's position, then yes, it could be in any orbital whose spatial wave function gives a nonzero probability for the electron being found in that position.

But in practice we never find electrons in atoms at particular positions. We don't measure their positions. They don't even have definite positions. We measure their energies and their angular momenta. And that tells us which orbital they are in.

f we find an electron near the nucleus then shouldn't it have less energy

No. The electron is not a classical particle. You can't relate its energy and its position the way you could for a classical particle in a classical orbit.

• BvU
Frigus
Thanks sir Mentor
If all we know is the electron's position, then yes, it could be in any orbital whose spatial wave function gives a nonzero probability for the electron being found in that position.

More precisely, before we measured its position it could have been in any orbital whose spatial wave function gives a nonzero probability for the electron being found in that position.

But after we measure the electron's position, it is no longer in the same state as it was before. It is now in a state localized at that position we just measured, and that state is not an orbital at all. It's not a state with definite energy or definite angular momentum. It's a different kind of state altogether. The electron isn't even bound to the atom any more--basically the process of measuring its position will have knocked it out of its previous bound state.

Once again, quantum mechanics does not work like classical physics, and the electron is not a classical particle.

• mattt