First and foremost, you're asking conceptual questions that
require a more involved discussion, either with your JC teacher, or
your personal/private tuition teacher. It is not feasible to
discuss these at length on an online forum.
As far as the A level H2 syllabus is concerned, you do not need
to (and it can be counterproductive to) concern yourself with some
of the more involved concepts and details.
If you're interested anyway, you could try posting your
questions on the Chemical Forums, for potentially more involved
discussions.
Brief comments :
1.1. Ignore 'filled' vs 'empty'. Not only is it not required, it
will be counterproductive and confusing to you (ie. an A level
student, assuming that's what you are) to dwell on this.
1.2. It is not the orbitals that possess energy, but electrons
occupying these orbitals that possess said energy.
1.3. A moot and irrelevant point. Since elements heavier
than copper are (as far as the H2 syllabus
is concerned) either period 4 'p' block elements (whose
chemistry do not depend on 4s and 3d orbitals) or period 5 'd'
block elements (whose chemistry depends on 5s and 4d orbitals, and
are beyond the syllabus anyway).
1.4. Is this a typo on your part? 4d electrons certainly possess
more energy than 3d electrons. Do you mean 4s electrons? If so,
here's the key to this classic riddle :
On
average, 4th quantum shell orbital electrons do
indeed have more energy than 3rd quantum shell orbital electrons.
But at the same time, it's also true that d orbital electrons
have more energy than s orbital electrons (for the same quantum
shell). Hence, these two 'opposing' trends counteract each other,
and it just so happens (in this universe at least), the latter
trend slightly outweighs the former trend. That's really all
there is to it.
2. It means less concentrated or focused. Think of it this way :
each orbital can only hold 2 electrons. Since 3rd quantum shell
orbitals are much larger than 2nd quantum shell orbitals, yet both
orbitals hold the same number of electrons, hence if electrons are
visualized as lights, then a filled 2nd quantum shell orbital would
be much brighter (ie. lights are more concentrated or focused)
compared to a 3rd quantum shell orbital, even though both orbitals
have exactly the same number of lights (ie. 2 electrons).
3. Think of it this way : wouldn't you need to possess more
energy in the first place, to resist the electrostatic pull of the
nucleus and remain further away from the nucleus, compared to an
inner shell electron? So whether the chicken or egg came first, all
these are beyond the concerns of the A level H2 syllabus.
4. The term ‘shielding’ only specifically refer to the
repulsive forces exerted by inner shell electrons on outer/ valence
shell electrons. As to your hypothesized, "if outer shell
electrons were to exert a repulsive force on inner shell electrons,
would that not increase the effective nuclear charge, since the
force should repel the electron closer towards the nucleus?",
it is a moot point for four reasons :
Firstly, the effect of the electrostatic attraction of the
positively charged nucleus far outweighs the relatively
negligible effect of your hypothesized phenomenon.
Secondly, chemical reactions concern only the valence electrons,
and thus as a practical functionality, the concept of effective
nuclear charge applies specifically to these valence electrons
which take part in chemical reactions. You are probably
arguing that your hypothesized phenomenon would indirectly reduce
the atomic/ionic radius and hence, increase the electrostatic
attraction of the nucleus for valence electrons. If so, that brings
us to the 3rd point.
Which is, thirdly, even if that is the case, it would apply to
all atoms/ions everywhere in any case, and consequently, we can
equally discount it's contribution towards meaningful comparisons
across atoms/ions.
Fourthly and finally, the practical functional definition of
effective nuclear charge is nuclear charge + shielding effect. And
since shielding effect has already been defined (ala circular
logic) as that of inner shell electrons repelling outer shell
electrons, to say shielding effect increases effective nuclear
charge would run counter to the point of a useful concept of
shielding effect. More pertinently, as mentioned in point #1,
your hypothesized effect is really rather negligible.
It's like, are you running out of a burning building
more because you don't wish to be burnt alive, or more because
you also happen to have a craving for a McSpicy meal at the same
time as you're running out of the building... deliciously hot
spicy firey stuff.
Hi, I would be grateful for some help with regards to the
following questions:
1. Statement: “4s orbitals
have lower energy than 3d orbitals for elements lighter than
copper.”
2. What is meant by orbitals becoming more diffused (e.g. when
principal quantum number increases)?
3. Why does the energy of the
electrons increase as the principal quantum number
increases?
4. Does outer shell electrons
exert shielding on inner shell electrons, or does the term
‘shielding’ only specifically refer to the repulsive forces exerted
by inner shell electrons on outer/ valence shell electrons?
Additionally, if outer shell electrons were to exert a repulsive
force on inner shell electrons, would that not increase the
effective nuclear charge, since the force should repel the electron
closer towards the nucleus?
