Idiot's question about periodic table
Ed Green
Why is the first row single, but all the remaining rows doubled?
Doesn't a new set of orbitals kick in with each increase in principal
quantum number?
"Vamos pa' Tabasco"
Bryan Reed
The rows do not correspond to principle quantum number. When you get
enough electrons in the core states, the relative energy levels shift--so
that, for example, a 3d state tends to have more energy than a 4s state by
the time you get enough core electrons to start filling either.
Similarly, 4d exceeds 5s by the time you get to it, and the f orbitals are
yet higher in energy. So the filling order (drawn to look kind of like
the periodic table) is:
1s
2s 2p
3s 3p
4s 3d 4p
5s 4d 5p
6s 4f 5d 6p
7s 5f 4d 7p
So, when you get up to the higher shells, adding angular momentum (going,
say, from p to d or d to f) adds more energy than increasing the principle
quantum number by 1. The filling order is violated in a few places, by
the way, in the d- and f-filling range. The p states are only a little
higher in energy than the corresponding s states. 2 electrons can fit in
an s subshell, 6 in a p, 10 in a d, and 14 in an f.
Without those core electrons altering the potential away from a pure
inverse square, you'd have all orbitals with the same principle quantum
number having essentially the same energy, as you do in hydrogen.
Have fun,
Bryan
Randy Poe
>
> I just realized I can't explain something very basic about the periodic table.
>
> Why is the first row single, but all the remaining rows doubled?
>
I don't understand what you mean by "single" and "doubled".
The first row has two elements. The second and third have
eight.
The 4th and 5th have 2+6+10 = 18.
The 6th and 7th have 2+6+10+14 = 32.
> Doesn't a new set of orbitals kick in with each increase in principal
> quantum number?
Oh, OK. I see what you mean. How come you don't start
adding "d" electrons till row 4? What happened to the
3d orbital?
Reaching back to chemistry class in the dim recesses
of memory, I think it has to do with energy levels. I think
that elements 21-30 have 4s full, and then 3d starts
filling up.
Now let me see if I can recall the energy considerations:
Starting with #18, Ar. We have 18 protons, 2 in 3s, 6 in
3p. There is a 3d shell available, but unoccupied in the
ground state.
Now we add another proton to the nucleus to give us #19 K.
We want to add another electron. Why doesn't it go into
3d? Answer: 4s is lower energy. But after 4s is full,
3d is lower than 4p. So the next 10 elements populate
3d. Only then do we start filling 4p.
Going up the next few rows in the periodic table,
we populate next: 4p, 5s, 4d, 5p (end of row 5),
6s, 4f (lanthanoids), 5d, 6p (end of row 6),
7s, 5f (actinoids), 6d, 7p (end of row 7).
I'm staring at www.webelements.com as I write this,
which has a lot of good stuff, but doesn't have the
orbital info I've seen on some big printed periodic
tables.
- Randy
Ed Green
>Message-id: <3BFC114A...@atl.lmco.com>
>Ed Green wrote:
>> I just realized I can't explain something very basic about the periodic
>table.
>>
>> Why is the first row single, but all the remaining rows doubled?
>>
>
>I don't understand what you mean by "single" and "doubled".
>
>The first row has two elements. The second and third have
>eight.
>
>The 4th and 5th have 2+6+10 = 18.
>
>The 6th and 7th have 2+6+10+14 = 32.
I was just about to clarify this, but...
<snip explanation>
Thanks to you and Bryan. I realized I couldn't
explain this while I was trying to explain the shape
of a water molecule in terms of orbitals.
The frightening thing is I don't even remember forgetting
that, after reading the explanation. I think Columbia
should dig out my transcript and erase that "A" in
freshman chemstry! Jeez.
You know, I once got an "A" in art history, but was
startled to see a B- on my report card, or whatever
they call it. So I go to the registrar and it very
clearly looks as if there has been an erasure and
a new entry on the master record (they still kept
paper records, I guess, in that dark age). Now
they denied up and down that it was possible that
the grade was changed after it was submitted
without their having a record of this...
Except I recall I had really pissed off the instructor
_after_ the term was over by expressing an interest
in an independent study project, then dropping it.
Never piss off a full professor. Strange things can
be made to happen.
"Vamos pa' Tabasco"
Steve Harris
news:20011121211715...@mb-mt.aol.com...
> Thanks to you and Bryan. I realized I couldn't
> explain this while I was trying to explain the shape
> of a water molecule in terms of orbitals.
>
> The frightening thing is I don't even remember forgetting
> that, after reading the explanation. I think Columbia
> should dig out my transcript and erase that "A" in
> freshman chemstry! Jeez.
Things like this happen. I was ridiculously along in chemistry before I
realized that the periodic table should really be printed as an elongated
thing with two really long bottom rows, but that (instead) every periodic
table I'd ever seen had those two rows snipped out and pasted on underneath,
as sort of an afterthought. I felt like somebody just seeing a world-globe
and realizing that Alaska actually *isn't* really this great huge island off
the coast of California, which it appears to be in the limited series of
maps which are the only ones you've ever seen....
My reaction of course was WHY DIDN'T YOU TELL ME THAT A LONG TIME
AGO???!?!?!? To which the teacher replied what they always do: something
along the line of "We didn't realize there was anybody out there so stuuupid
as not to know it. Especially by the time they had gotten to your level.."
Grrr.
> You know, I once got an "A" in art history, but was
> startled to see a B- on my report card, or whatever
> they call it. So I go to the registrar and it very
> clearly looks as if there has been an erasure and
> a new entry on the master record (they still kept
> paper records, I guess, in that dark age). Now
> they denied up and down that it was possible that
> the grade was changed after it was submitted
> without their having a record of this...
>
> Except I recall I had really pissed off the instructor
> _after_ the term was over by expressing an interest
> in an independent study project, then dropping it.
>
> Never piss off a full professor. Strange things can
> be made to happen.
No, this is only professors of art history. Where the present controls the
past, ala 1984. No professor of chem or physics or math would have been able
even to conceive of doing that.
Serves you right for taking such classes.
SBH
--
I welcome Email from strangers with the minimal cleverness to fix my address
(it's an open-book test). I strongly recommend recipients of unsolicited
bulk Email ad spam use "http://combat.uxn.com" to get the true corporate
name of the last ISP address on the viewsource header, then forward message
& headers to "abuse@[offendingISP]."
> "Vamos pa' Tabasco"
Ed Green
>Message-id: <9thuk1$kps$1...@slb6.atl.mindspring.net>
>"Ed Green" <null...@aol.com> wrote
>> You know, I once got an "A" in art history, but was
>> startled to see a B- on my report card ...
>No, this is only professors of art history. Where the present controls the
>past, ala 1984. No professor of chem or physics or math would have been able
>even to conceive of doing that.
Very good! I didn't think of this in terms of the subject
matter. I had been historically reevaluated.
I have always maintained a fondness for van Eyck
after that class though. In principle.
I am looking at an interesting artistic object as we
speak... a preserved stick insect, under glass. The
body is about 6" long, with 6 very twiggy appendages.
Perhaps you have seen such things in life. But this
one has a difference: it also has a set of wings. It
is quite real.
I can't imagine it was a very powerful flier, but if you
saw this monster leaping out of a tree, the effect
would be bad on the faint hearted.
"Vamos pa' Tabasco"
Lucius Chiaraviglio
fritz again.]
bwr...@u.washington.edu (Bryan Reed) wrote:
>In article <20011121134111...@mb-fz.aol.com>,
>Ed Green <null...@aol.com> wrote:
>>I just realized I can't explain something very basic about the periodic table.
>>
>>Why is the first row single, but all the remaining rows doubled?
>>
>>Doesn't a new set of orbitals kick in with each increase in principal
>>quantum number?
>
>The rows do not correspond to principle quantum number. When you get
>enough electrons in the core states, the relative energy levels shift--so
>that, for example, a 3d state tends to have more energy than a 4s state by
>the time you get enough core electrons to start filling either.
>Similarly, 4d exceeds 5s by the time you get to it, and the f orbitals are
>yet higher in energy. So the filling order (drawn to look kind of like
>the periodic table) is:
>
>1s
>2s 2p
>3s 3p
>4s 3d 4p
>5s 4d 5p
>6s 4f 5d 6p
>7s 5f 4d 7p
Does anyone have a handy table like this for the filling order in a
nucleus (that is, as one adds more protons or neutrons)? The mathematical
rule for determining the number of elements in each row of the periodic table
is easy enough to understand and predict, but the "magic numbers" (numbers
corresponding to all shells being either filled or empty) of nuclear structure
do not fit into an obvious mathematical pattern (they may follow some
mathematical rule -- just not an obvious one; if some rule is known, I'd like
to know what it is). Proton "magic numbers" are 2, 8, 20, 28, 50, 82, and 114
(predicted); neutron "magic numbers" are 2, 8, 20, 28, 50, 82, and 126 --
not even the same as the proton "magic number" at the end of the sequence of
numbers. What's going on -- electrostatic repulsion causing inner shells to
be partially emptied as outer shells are filled?
--
Lucius Chiaraviglio
E-mail address is approximately: lucius1@telo_large_urban_area.com
To get the exact address: ^^^^^^^^^^^^^^^^^
Replace indicated characters with common 4-letter word meaning the same thing
and remove underscores (Spambots of Doom, take that!).
Ollie Brennan
momentum zero, 2 spin states, so there are only 2 possible states in total.
The next highest energy level has orbital angular momentum =1, and also
spin=+1/2 or -1/2 so there are 6 possible states - ang.mom=-1,0,1 and 2 spin
states for each. This pattern continues, which is why the pattern in the
periodic table emerges.
A new shell kicks in with every increase in principal quantum number (n)
because, if you solve the Schrodinger equation for Hydrogen (or, if you're
adventurous, any element) the spherical harmonic component depends on
l(ang.mom)=n-1 at maximum, and there are 2l+1 possible states for each l,
multiplied by 2 for spin.
Hope that answers what you want, cos the question isn't particularly clear
(there are 2 elements on the first row).
"Ed Green" <null...@aol.com> wrote in message
news:20011121134111...@mb-fz.aol.com...
Ed Green
<9uts5v$169$1...@news.ox.ac.uk>
>It's about shells, yep.
...
>Hope that answers what you want, cos the question isn't particularly clear
>(there are 2 elements on the first row).
Thanks for the reply, but see the remaining
replies for what I was really asking.
>This pattern continues, which is why the pattern in the
>periodic table emerges.
>A new shell kicks in with every increase in principal quantum number (n)
Right... and what you might wonder from this picture,
is why the second and third shell and then the fourth and fifth shell have the
same number of electrons. Aren't
there new orbitals kicking in with each increase in n?
The simple answer to this idiot's question was that
a shell, as you remind me the terminology goes,
does not correspond to completely filling the orbitals
associated with a given principal quantum number.
The electrons sometimes take a breather and defer
filling all the states available for a given n until the
next shell. :)
"Vamos pa' Tabasco, du rassenhassender Glatzkopf!"
Ollie Brennan
left) 2p (6 atoms on right), 3s 3p, 4s 3d - the energy levels of 4s and 3d
are similar so the electron goes into the leve with the lowest energy. It
gets all complicated there with spin-spin repulsion meaning you get 3d(5)
4s(1) before 3d(6) and 3d(10) before 4s(2) etc but the general scheme is
that a new orbital at a higher energy kicks in with each increase in
principal quantum number, as you get further and further from the nucleus
the energy levels of the shells mix up a lot more so the structure of atoms
is more complicated.
"Ed Green" <null...@aol.com> wrote in message
news:20011208183059...@mb-fz.aol.com...