Example electron gain enthalpy - Elements & Periodicity Video Lecture - Class 11

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classification of elements part 20 is
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part 1 - part 19 let's take one example
our electron here enthalpy the question
is which of the following will have the
most electron gain enthalpy and this
will have less oxygen and sulfur so you
see this oxygen has - 141 and sulfur has
minus 200 but as I told generally the
trend is if you go down the group it
becomes less negative but here if you
see and fluorine and chlorine loss is
one example similar pattern where it
increases actually it becomes more
negative and then follow the trend of
becoming lessening if you see minus 140
when it becomes minus 200 right and then
started decreasing with a negative sign
here if you see - see 28 it became all
the more negative and then this thing
why it is happening so this is happening
because if I am taking oxygen sulfur
here oxygen is very small very small see
the atomic size is very small that's why
a new electron it is added right the new
little is added it repel so the electron
gaining that V is less here I mean less
energy liberated but if you start from
sulfur it follows the pattern because
sulfur is competitively Oh kick kind
size so after that you add electron it
lose energy atom electron in this it
lose less energy lose less energy less
energy and then continues but in case of
oxygen itself it is very small in size
very small in size
thus the moment you are extra electron
it repel right Isabel the
little a lot lot of a person is there
Versailles is very wrong
same taking Florian also the size of
flooring is very small so the extra
electron added it is not welcome that
much because the floor in size is small
and interprets now the question is which
of the following has most negative
electron in enthalpy and which has least
so if you talk about phosphorus sulfur
chlorine so if you see my phosphorus
sulfur and chlorine here part of period
3 right they are part of period 3 and
where is my fluorine mone is somewhere
here period
right this is p2 this is peak that's how
it is my phosphorous is 15 group element
16 then 7 km that's how it is arranged
the priority right now I have told that
as we go from here to here in this
direction the electron or gain enthalpy
become less negative right sorry more
negative while because the atomic size
or decrease I am going from here to here
the atomic size is decreasing right size
is decreasing so it's becoming all the
more negative so chlorine will have you
do is arranged in the order it will be
phosphorus sulfur chlorine right so this
liberate more energy so leave it that
means crawl in chlorine will liberate
more energy then suffer then phosphorus
correct now the question is chlorine
they should be put F now since this guy
F is above here it should
logically have more you should liberate
actually more energy including on adding
new liquor but as I told fluorine has a
very small size of electron atom so
fluorine liberates less energy because
the new electron that you Adam Toren it
get repelled by the small size correct
so I have something like this CL so
fluorine gave me somewhere here
somewhere here right so I have a
optional phosphorus sulfur chlorine or
chlorine or phosphorus Laureen sulfur
Akron which I am Not sure no not sure
which is option but the question asked
me which in his list
Lee sin which is max in both case if you
see that this is my maximum negative and
this is my niche negative because
maximum liberate energy liberated is
negative and minimum liberated is third
this is the way to find also if you want
we can do from electronic and generation
also so for fluorine you can see atomic
number is 9 so I'll say 1s2 2s2 2p5
correct let's say for phosphorus
phosphorus L is 15 atomic number so I
will say it is 1s2 2s2 2p6 3s2 3p3 then
i have sulfur 16 1s2 2s2 2p6 3s2 3p4 and
then I have to write 17 that is 1 as to
us to 2 is 6 3 s 2 Chifa now you see
this guy is half it right so it is
stable others are not stable so that
means this guy will liberate minimum
energy correct why because phosphorus
the outermost sub cell is half it so it
will liberate
minimum energy is stable a stable so by
minimum energy liquid it is phosphorus
that means it is least negative now
we'll talk about the maximum one so if
you see in this case fluorine and
chlorine the moment you get one electron
in this it becomes seven so this is not
in question sulfur is not in question
the answer will be either fluorine or
chlorine
correct fluorine are going in for end if
you see the size is small so the moment
you add extra electron here it gets
rippled correct size one small size
means more a person here if you see is
very small actually very simple size
it's very very small size this cleric
the sigh is decent so the represent is
less it can take this so chlorine will
have maximum negative shows you have
either way of solving the question
either you write the electronic
configuration and try to find y adding
an electron is 0 in which case and not
favorable in which case or you can erase
the elements in the periods of loops and
then you can find they should will have
or most negative electron in college and
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