Yup, that one sheet of paper which defines the entire foundation of chemistry ( and our high school). That eklota less than 2 mm paper ,which defines everything around you. Yup, that's exactly what we are going to talk about again (after almost half a year after my previous blog on the Periodic Table (Man, time flies) )
If u haven't read my previous blog on the basics of periodic table click on the link below
But, this time it's going to be a little different... This time instead of going in detail of every characteristic of the table , we are going to look at only the exceptions.
The common problem encountered with every high school student is remembering the exceptions in the trends of the Periodic Table. And the exceptions the exceptions have. (No, I am not going crazy)
DISCLAIMER:- If you haven't completed the Periodic Table chapter in the NCERT textbook, the terms I use might sound very vague, so don't panic, I am pasting links to detailed explanation of each new scientifical term I use and I am planning on posting another blog with detailed explanation of each term and explanation soon )
ATOMIC RADIUS
The average distance of valence shell electrons from nucleus is called atomic radius.
THE USUAL - Increase down the group, Decrease across the shell ( Check out https://ncert.nic.in/ncerts/l/kech103.pdf Page.13 Right hand side for mroe details)
THE EXCEPTIONS
S/P block
In the III A group , the size of Aluminium and Gallium is nearly same thought they are in different groups.
Why? You may ask
This is due to a phenomena called D-Block (transition) contraction
( Brief version, As we move down the group from Al to Ga , 18 electrons increases , out of which 10 go to the 'd-orbital' (another long story) which have poor screening effect (a longer story) this causes the outer electron to be attracted more by nucleus and hence the decreased size)
so the actual order is B < Ga < Al < In < Tl
D block
In the transition series, the elements of the period
3d < 4d ≈ 5d
This is because of the poor shielding effect by f-subshell
Hence, Ti < Zr ≈ Hf and the pattern continues throughout.
but there is an exception to this exception (See! I wasn't kidding)
Sc < Y < La < Ac -- follow the usual pattern though there are in the D-block
IONISATION POTENTIAL OR IONISATION ENTHALPY
The amount of energy required to remove an electron from an isolated gasous atom
THE USUAL - Increases across the period, decreases down the group ( https://ncert.nic.in/ncerts/l/kech103.pdf , page 15 , Right Hand side of the NCERT)
THE EXCEPTIONS -
CASE .1
Li < B < Be < C < O < N < F
Na < Al < Mg < Si < S < P < Cl
( For Detailed explanation, click here _ it redirects to my previous blog where I have explained this in great detail)
CASE. 2
Group IA and IIA
Li > Na > K > Rb > Fr > Cs
Be > Mg > Ca > Sr > Ra > Ba
This is the consequence of the Lanthonoid contraction (the poor shielding effect of the f - subshell)
CASE. 3
B > Tl > Ga > Al > In
( Galium as it has the effect of D-shell (transition) contraction and Thallium got a double effect of both the Lanthanoid and D - shell contraction)
C > Si > Ge > Pb > Sn
(Pb is smaller than Sn cause of Lanthanoid contraction)
CASE. 4
We read that due to lanthanoid contraction ,
3d < 4d ≈ 5d, and the Ionisation potential potential is depended on the size of the element - the smaller the size, greater the Ionisation potential
Hence,
5d > 3d > 4d (in decreasing order of Ionisation energy)
ELECTRON AFFINITY
(This is what happens when the destructive nature of Physics rubs on Chemistry, -- Have no idea on what I am talking about, Well, read this now! -- my desperate attempts on linking physics, chemistry and maths together (ง •_•)ง )
The amount of energy released (or absorbed) when an electron is added to the outermost shell of an isolated gasous atom
THE USUAL :- The amount of energy released increases across the group, decreases down the group.
THE EXCEPTION:-
CASE. 1 -
Unlike other atoms which release energy, our dear Nitrogen demands energy for the addition of electron (due to half filled electronic sub-shell ) (talk about a hard bargain)
But unlike Nitrogen, though the entire Nitrogen family (i.e 15th group) have half filled electrons, only Nitrogen absorbs energy when an electron is added -- P , As, Sb, and Bi release energy but the magnitude of energy released is lesser than expected.
CASE. 2-
Noble gases are very stable in nature and they don't like their stability to be distrupted. They donot allow the addition of electrons and If we force an electron, they will demand very very very high energy.
CASE. 3-
Alkali Earth Metals due to the high penetrating power of s 'orbital' absorb energy when an electron is added.
CASE. 4
According to the previous trends, we know that the 3rd period is more larger than the elements in the 2nd period. The 2nd period element, cause of it's small size, experience higher inner-electronic repulsions making it tougher to take in extra electrons.
Hence, 3rd period > 2nd period
In conclusion , the trend absorbed down these groups will be
Cl > F > Br > I
Well, that's all folks! Keeping up with the new tradition, ending this blog with a surprisingly relatable joke ^^;
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