>>11884204>>11884857You can infer the electronic arrangement from the configuration, however, I would consider it the best strategy use when you want to find the electronic arrangement.
>1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6,By looking at this we can group the shells together:
>1s2 That is shell 1 and it is telling us it is full (give the s2 since the s orbital can only fit two electrons). Again, the 1 indicates shell 1.
Total number of electrons: 2
>2s2, 2p6The second shell here, it is also full. Two full s orbitals (2 in the s) and p orbitals (6 in the p) with a total number of 8 electrons (refer to how electrons proceed 2, 8, etc. in ascending order).
Total number of electrons: 8
>3s2, 3p6, 3d6**(This section may cause confusion as it isn't as straight forward as the previous two. Also I'll add that for all intents and purposes you'll find the 4s2 orbital coming before the 3d6 orbital because of it's lower energy, however, given the context of trying to find the electron arrangement we can ignore that fact for now only. )**
The first thing you'll notice is that the 3rd shell is not filled completely. A complete 3rd shell requires 18 electrons, here there is only 14 (2 + 6 + 6), you might ask why iron has a 4s2 orbital then when those 2 electrons could be used to fill the 3rd shell. This is because of the periodic table relationship I stated previously. The period of an element determines the number of shells it will have, give iron is a period 4 element it will have 4 shells thus the electrons must obey this so instead of having a full 3rd shell, 2 electrons are reserved for the 4th shell.
Total number of electrons: 14
>4s2Due to reasons I stated earlier, iron has a fourth shell. It is a full s orbital with 2 electrons (since this is iron's outermost shell iron therefore has 2 valence electrons).
Total number of electrons: 2
Now just place the total number of electrons of each respective shell into the electronic arrangement format.
