# Electronic configuration in d-block

According to Bohr-Bury rule, 4f and 5d orbital come after 6s orbital. But if I search for the electronic configuration for Os or any atom in d block for that matter, they give the electronic configuration as 4f 5d 6s instead of 6s 4f 5d

Why does this happen ? why is S orbital written in the end even though it has less energy Can someone please explain ?

• What is "Bohr-Bury rule"? This looks pretty much like Aufbau approximation known by a plethora of other names, but Bohr-Bury rule is something new (at least to me). Anyway, chemistry.stackexchange.com/questions/141708 seems to be related. Aug 11 at 13:00
• Thanks, but my question is not on the order of filling of orbitals per say, but the order with which each orbital is portrayed on the internet. For example if you search for the electronic configuration of Ir (Iridium) in the internet or any reliable source, you get 4f(14) 5d(7) 6s(2) which is right, but why not 6s(2) 4f(14) 5d(7), same answer but this one is ordered in such a way that it follows the order increasing energy of orbitals. Energy wise 5d has more energy than 4f and 6s respectively so why do they have to mix the order up can't they just follow the order of increasing energy ? Aug 11 at 13:24

It doesn't matter the way you write it. 4f 5d 6s is the same as 6s 4f 5d. The first one is ordered by energy and the second by the way the orbitals are filled. Even though, you must note that the 5d$${^1}$$ fills first in the element lanthanum [Xe] 6s2 4f0 5d1 ^[1] https://en.wikipedia.org/wiki/Electron_configuration