In an atom, electrons will fill up orbitals in order of increasing energy . The principle quantum number determines the “energy level” of the orbital. Orbitals with lower values of n are usually associated with lower energy and will be filled first.
Another frequently asked question is “Why do electrons quickly fall to lower shells?”.
Electrons (negatively charged) fall into electron shells around Protons (positively charged) because it results in a less energetic state . The reason that protons and electrons don’t just “stick together” is that as electrons are attracted closer and closer to protons, they lose potential energy (resulting in a “lower energy state”).
Some believe that when an atom or ion receives electrons into its orbitals, the orbitals and shells fill up in a particular manner. A subshell is particularly stable if it is half full or full.
You might be wondering “What allows an electron to skip into a higher shell?”
One source stated in order for the electron to skip back into the ground state (at lower energy), an interaction must occur.
Why are electrons removed first from the outermost shell?
This is because the outer shell is maximum shielded from the influence of the nucleus, and hence lower energy is required to extract electrons from the outermost shell than from an inner shell. Since 4s orbital lies in the fourth shell, and 3d in the third shell, electrons are removed first from 4s .
The explanation is actually quite simple. Let us discuss how an electron moves from a lower energy level to a higher energy level first. Electrons are negatively charged and move around the other edges of the atom, and protons are positively charged and are at the center of the atom (nucleus).
Do electrons fill the lower energy levels first?
The Aufbau diagram can be used to determine the order of filling of atomic sublevels, although there are some exceptions among the transition metals. The Aufbau diagram shows the order of filling of atomic sublevels in order of increasing energy .
Electrons can’t fall into lower energy levels if those orbitals are already filled. That’s because of the Pauli Exclusion Principle . Electrons can indeed jump to higher energy levels, but only when energy is put into the atom.
Do electrons lose energy when moving shells?
When electrons gain or lose energy , they jump between shells as they are rotating around the nucleus. Then, as they lose energy by emitting photons, they might move back to the second energy level shell or even to the first energy level shell.
So when it gains some energy (it may be in the form of charge) and gets energy equal to or more than equal to the next shell it jumps up to the next shell and radiates the extra energy (if it gains more energy than that shell) to be stabilised. Here’s the spectrum and transition details: Hope it helps you.
Why does an electron lose energy when it comes close to nucleus?
More stability implies less energy. This is a general rule. As an electron comes near to the nucleus, as the distance decreases the force of attraction increases because the force is inversely proportional to the square of distance .
Atomic electrons lose / gain energy when transferring from one orbital to another and hence emitting / absorbing a photon. Free electrons (by which I mean electrons that are not part of an atom) lose or gain energy by scattering inelastically with atoms or molecules .