# How many empty orbitals do elements have?

A student was contemplating a question regarding elements with "no empty valence orbitals." An argument was made that elements all have infinite number of valence orbitals.

Every atom basically has an infinite number of shells. The thing is that almost all of those shells are empty (they don’t have electrons in them).

https://van.physics.illinois.edu/qa/listing.php?id=1224

So it is facile to say that, say, the fluoride anion has no empty valence orbitals on the basis of it having 8 valence electrons and the $2n^2$ rule (where n = 2)?

• While it's true that electron orbitals could go on forever, each element has to have a practical limit. For example, a hydrogen atom can easily hold 1 electron because it has 1 proton. A hydride can have 2 electrons and a -1 charge. However I don't think you can jam 10 electrons on a hydrogen even if the orbitals technically exist to hold them. I don't know what the best way to describe the number of orbitals on an atom is, but calling it infinite may confuse some students. Commented Aug 19, 2014 at 16:31
• @user137 its important to note that once you have more than 1 electron, the hydrogenic orbitals are an approximation anyway. Though from a simple perspective you could just say that after a certain point those orbitals have a positive orbital energy and that can explain why you wouldn't ever have $\ce{H^{9-}}$. You could access these orbitals by excitations if you only have 1 electron.
– Tyberius
Commented Dec 14, 2017 at 17:12

In my view there is an important difference between empty orbitals and empty valence orbital. There are an infinite number of orbitals, a finite number of filled orbitals, but only one valence orbital.

The definition of a valence electron is usually something like, "The electrons in the outermost shell are the valence electrons--the electrons on an atom that can be gained or lost in a chemical reaction." Therefore, a valence orbital would be the orbital holding those electrons. If the valence orbital is full, it is full; there are no other valence orbitals.

Based on this understanding, it would be correct to say "the fluoride anion has no empty valence orbitals."

• +1, I agree that the word valence is critical there, and it can be made rigorous by reference to the principal quantum number. Commented Aug 19, 2014 at 16:54
• In general I agree. However, there is further confusion when you get to the transition metals and above where there can be several incomplete orbitals. Commented Aug 19, 2014 at 22:09
• I generally agree, but I am a little confused, why you used one valence orbital. Did you mean valence shell? I am just uncertain of how to fit degenerate orbitals, like in oxygen, into this. || In computational chemistry we like to avoid the term valence orbital, being the previously stated one reason. It is more practical to think of occupied and unoccupied (or virtual) orbitals only. It is also impossible to measure an unoccupied orbital, so speaking of it is in a fuzzy grey area... Commented Aug 20, 2014 at 4:08
• @Martin Yes, "shell" would have been a better choice of words.
– ron
Commented Aug 20, 2014 at 13:03
• @Jon Custer Sometimes it gets a bit tricky just where to draw the line on what information to include and where to focus the answer.
– ron
Commented Aug 20, 2014 at 13:31