Why do the orbitals at different energy levels overlap while electrons cannot jump between energy levels without absorbing or releasing energy?

Question

Also, looking at their orbitals, how can electrons in 2p shell be as close to the nucleus as 2s or 1s electrons for "90% of their time"? Because how can we get different energy levels like this, that electrons cannot simply switch between without an energy exchange..

Thank you..

Answer 1

There are two quantum numbers that determine energy : The principal quantum number (the higher n is, the higher the energy because the orbital is farther as n increases) and the azimuthal quantum number (the higher l is, the more complicated the orbital l = 0,1,2 is s, p, d which means that the electron is more constrained and higher energy as l increases). This is why things get complicated with transition metals as 4s and 3d switch energy level as the d orbitals are populated (4s is higher energy with n = 4 and l = 0, but 3d is higher energy because l = 2 - the d electrons do not push each other out as much as they push out (or shield) the more distance s orbital)

Answer 2

Electrons in different orbitals may overlap without transitioning between, because electron orbitals are somewhat diffuse things. If we could "interrogate" a particular electron, we might "find" it at various places, at different times. But its quantum state, NOT its instantaneous position, is What It Is. So, many different electrons COULD simultaneously be in a particular place around an atom, BUT that is only possible because they have different quantum number sets, and are acting like waves (which, after all, can pass right through each other on the surface of the water). The electrons simply ignore each other!

There is a qualification to the idea that electron clouds are big puffy things all the way around an atom. And that is, that higher orbitals and suborbitals have NODES in their clouds -- places (spherical or radial shapes) where the electron will NEVER be found, BUT the electon exists simultaneously on both sides of that gap! That's a property of a standing or travelling wave on the water, too -- it exists on both sides of a node!

Now, that's not the case for "free electrons", namely, those not on an atom. Those repel each other fiercely, by electrostatic force.

With respect to your followup question to Jacques D. above, there are several sorts of modification to the energies you usually observe for various orbitals and suborbitals, that give the general organization to the Periodic Table. One big one is that a half-filled suborbital (such as 3d5) is more stable than the 3d4 and 3d6 on either "side" of it, so it will "borrow" a 4s electron to fill itself, for atomic manganese (or any ion with the same number of total electrons). The same goes for a completely-filled suborbital, so for Zn atom, it fills the 3d10, and then loses BOTH 4s electrons to form a Zn(2+) ion, for example.

-- Cheers, --Mr. d.