Electron Configuration Flashcards
Electron Configuration Order
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
Why does 4s2 come before 3d10
The aufbau principle explains how electrons fill low energy orbitals (closer to the nucleus) before they fill higher energy ones. Where there is a choice between orbitals of equal energy, they fill the orbitals singly as far as possible (Hunds rules).
If 4s orbitals are higher in energy than 3d orbitals, then why do electrons fill up in 4s before filling up in 3d?
The 4s sublevel is only lower in energy if there are no electrons in the 3d sublevel. According to the Aufbau principle, the 4s sublevel is filled before the 3d sublevel because the 4s is lower in energy. As the 3d sublevel becomes populated with electrons, the relative energies of the 4s and 3d fluctuate relative to one another and the 4s ends up higher in energy as the 3d sublevel fills. This is why when electrons are lost from the orbitals of the transition metals, they are lost from the 4s first because it is higher in energy.
When adding electrons for anions
you add them as usually you would do for electron configuration
When removing electrons for cations
you remove them not from the END of the electron configuration but you always remove electrons from the shell that is furthest away from the nucleus.
When removing electrons, they are taken away from the
4s orbital first as it is further away from the nucleus, and then electrons are removed from the 3d orbital.
Which two atoms are exceptions to the rule when it comes to electron configurations?
Chromium, copper
Why are Chromium and Copper exceptions to the electron configuration rules?
Completely filled sublevels are more stable than partially filled sublevels. A sublevel which is exactly half filled is more stable than a partially filled sublevel which is not half full. In both examples, an electron moves from the 4s sublevel to produce a 1/2 full 3d (Cr) or completely filled 3d (Cu). This gives the atom greater stability.
