hi everyone so I wanna continue talking about
to trend in ionization energy and um you
a should notice that I spent quite a bit of time talking about an incision energy
and now I'm gonna talk but the exception to a couple of the
a elements the to the trend in an incision energy and the reason I spend
so much time talking about it is because
a I want you to put to to get um
you know it did do kinda concept here of explaining
that trend and as well as the exception
and really what we're relying on as I said from the beginning is
our understanding of this equation which is the equation of the binding energy of
the electron
said nucleus okay but if you can explain what's going on with this equation with
respect to Z effective
and and a then you should be able to explain pretty much you know the
majority of the cases self
uptrend an exception so right now we're gonna do is win go into the
exception to train and ionization energy so
what we'll do is just gonna go back to this plot here which is the plot of the
trainers Asian energy and
point out a couple of the exceptions here and try to rationalize why
those exceptions exist the first exception you notice and I mentioned
this but I was pointing up the trend
what's that in pure period to when we see this
um increasing trend as you go from the left to the
right side of the period but you also notice a couple things that
a violate that trend and the first one is this beer
beryllium versus boron violation okay
s we know the trend should go up so in other words from the ileum tube or on
we should get an increase not decrease the question that is why is there a
decrease
is set up an increase when you wanna answer questions like this what you have
to look at is so waz what is the electron configuration
of burly amanpour on and what a
specifically makes the
electron in boron in this case easier
to remove 2i a nice in comparison to the electron
in beryllium okay and you have to rationalize it again based on your
understanding of
see see effective principal quantum number
shielding and penetration you know combine those
all those factors the current think about what is the most reasonable
explanation
that you can come up with to explain this particular
exception to the threat so let's look at the explanation that
um we have here for more on Versus brilliant
so borough on is bigger um we expect the
a a ionization energies be higher but it's actually instead
smaller so why well
first thing like I said it's look at the electron configuration so borough on
5 electrons looks like this early in for like trance looks like this
what's the main difference the main differences in boron
the first ionization energy corresponds to remove a love for 2p
electron in Burley 'em the
removal of a 2s electrodes now
as we talked but when we talk but the energy of electrons in orbitals
I set their that the 2p
orbital is less stable then the two SO
to orbital and the reason for that is because self
electoral penetration um the 2s or bill is able to penetrate remember to the 1s
space
wheres the 2p lectern cannot and as a result the 2s
orbital becomes more stable know if the 2s electorate is more stable
then to remove it would require
higher energy in comparison to the 2p electrons
and that's why we see instead of a increase here we see a decrease because
the borough on
the 2p elector in boris actually easier to remove in comparison to the
2s electron beryllium now you might argue that
um there's an increase in
Z in that Tomic number going from
Berlin tube or on going from four to five and
when that then make a difference in terms of the stability of the other
up bore on versus the burly 'em
electron well as it turns out you we see that
the exception exists so clearly there is steady increase in atomic number
but that atomic number increase apparently it's not enough
to make a difference in terms of the stability of the boron
instead the difference in the stability of the
s versus the PR battle dominates a or
as a larger difference in comparison to the increase that you gain from
an increase in the atomic number and that this is a really important point to
make at this point because
when you're rationalizing the six ep Shin
you almost always have two factors that might go against each other
okay and when that happens you have to basically make a
you know he we without access to actual number send
you know calculations what we have to rely on this the experimental
observation
and if the experimental observation tells is one thing
than what we have to do is say the theory has to explain what we observe
experimentally
so in this case we have to conclude that the increase in ze
in the atomic number going from four to five somehow doesn't compensate
for the difference in stability between the two p for sister 2s electron so you
still see that
decrease in ionization energy okay
so that's something you need to keep in mind because like I said there's always
two competing factors lot of times and one factor will predict one way in the
other factor would predict the other way
the question is which one is you know more important in that particular
context which one
is the larger one okay and that's something you need to start to develop
the skill of
being able to um understand that
even though there are many many factors that might affect something
one or two factors usually are more dominant and therefore more important
than the rest of them
let's take a look at the second exception here which is the exception
though we observe when we go from nitrogen to oxygen
again we expect an increase in a decision energy but what we see said
decrease
United station energy between into all
what you can do at this point is you can pause the video and start think about it
on your own and think about how old
you can explain this exception and
what I would start with again is electoral conflagration because that's
really the basis of how would you explain
all of these things to start with electron configuration
and if I go and draw the electron configuration
and again this particular case I'm actually using the box diagram because I
want to highlight certain things
about the lights on cover Gration the box diagram that I can't do with the
written form a you notice that nitrogen
past seven electron sausages eight electrons so
agenda looks like this oxygen looks like this
what's the main difference again what you notice here's actually
the all they both have valence electrons in the 2s and 2p
orbitals okay so the from that perspective there's no difference
the difference though exists when you look at where
those feeling that electrons are located um would respect each other
in nitrogen the tree valence electrons the PR bills are
located in one orbital each 2px to peel away into pz
in the oxygen atom you notice that because there's 24
there's an additional well electron
in the oxygen atom versus the national anthem that the four selectors actually
located
in one up the p orbitals that already has one electron in them
and as a result when you put two electrons in the same orbital
they're both the same charge so we know from electrostatic
theory that they're going to repeal against each other
and death rate Paul Shin if you think about it
will make this electrode what if these two electrons easier to remove
then an electron that is only single
because there's a little bit a repulsion which makes the electron less stable
complete in comparison to an electron that a single and
if they repulsion makes the electron less stable
that means the electron this easier to I a nice thats easier to I know stan is
ionization energy were actually dropped instead of increase
and that in fact is what we observe here we see a drop in air is Asian energy
instead of an increase
and again you can make the argument as um
I said before with boron and beryllium that
isn't there an increase in atomic number between the 728
it is through you have more protons here but however
somehow that increase in proton
doesn't compensate for this difference in the repulsion that you gain when you
get that
oxygen and you notice actually if you look at both of these
drop here they're not big drop straight there's a disagree up in energy here but
that
change that drop its much smaller than increase you observe when you go from
one element to the other one
so in fact disease or the atomic number does make a difference it does
increase it does make it harder for you to remove that elects one however you
have this
conflicting or opposite effect coming in from
the repulsion and in this case again
as I mentioned earlier the repulsion actually dominate so it's more important
or has a larger affect
and as a result overall the total fact results in
the decrease in amortization energy is suppose to an increase in an incision
energy
we're done with up discussing and is Asian energy both the trend and the
exception
but again essay started with this video I want to remind you again
the next step you know a couple trance that I talked about I would
sort of go through them rather quickly than what I've done with diet is Asian
energy and the reason is because
I really spend quite a bit tight on their decision as you because I want you
to
use the same reasoning I use for
explaining a trend explaining the exception
um on these other trend 7 to talk about in
other videos and upcoming videos and I hope
the you you get a feel for what it iz that's important
when we're trying to look for explanation
a in periodic trends and again that is
what is the effect on the trend on this equation right here
particularly on the sea affect the value and and and value