00:01
So, we have to write electronic configuration here and to write the electronic configuration, we must know that atomic number is equal to the number of protons.
00:10
And we know that for a neutral atom that is which is electrically neutral and consists of equal number of positively charged protons and negatively charged electrons.
00:22
So that means that the atomic number for that neutral atom will be equal to the number of electrons we will fill those electrons in the energy levels and the shells and sub -shells accordingly and this is called the electronic configuration so first of all we have aluminium so the elemental simple for aluminium is al and its atomic number is 13 so that means it has 13 electrons so the electronic configuration will be 1 s2 2 to 2 to be 2 to be so if you count them so total 10 electrons are there we have to fill three electrons more so that will be 3 s 2 3p1 so this is the electronic configuration here note that we are using we are following the off principle which says that the electrons must be fill in the lower energy orbitals first and then we will move on to the higher energy orbitals according to the higher energy orbitals according to to the energy order okay and the energy order is decided on the basis of n plus l rule where n is the principal quantum number which tells us about the shell 1 2 3 4 5 and so on and l is the azimethyl quantum number it tells us about the sub shells fpdf okay so here suppose for example to understand i am telling you here this is 1 so this is the principal quantum number so 1 plus following the n plus l rule so 1 plus for s for s the value for l will be 0 so 1 plus 0 will be 1 so next is 2 s so here that means 2 the n value is 2 the s value is 0 so 2 plus 0 2 so now you can see 1 and then 2 and then i have here 2 p so 2 p means i have n value 2 for p for p the l value is 1 so that is 3 for 3 s so n value is 3 s value is 0 okay for 3 p for 3 p i have here n value 3 and p value is 1 so 3 plus 1 4 so you can see that the n plus value is increasing okay n plus l value is increasing and this determines the increasing energy order so this is how we fill up the electrons following the off -po principle so now moving on to the next part so we have iron this time and it has elemental symbol f e and atomic number is 26 so it has 26 electrons so the electronic configuration will be 1 s 2 s 2 s 2 p6 then 3 s 2p 6 3d 3d 3d 6 3d 6 4 so in this way we filled the 26 electron here and here one thing is to be noted this is very important this may confuse you.
03:53
Here i have written 3d6 4 s 2.
03:56
So if you follow off the principle so that says according to that n value is 3 for d the value will be 2.
04:06
So this will be 5.
04:08
For 4 s that will be 4 plus 0 for s for s for the value is 0, okay, l value.
04:16
So that is 0.
04:17
So that means 4.
04:18
So you can see that 5 is greater than 4.
04:21
So it must be come here, right? so if you write according to that, the electronic configuration should be written as 4s2 3d6...