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Panopticon
06-02-2003, 10:07 PM
On my homework, I came across a reference to a molecule with a formulae of XeF4. Is such a molecule possible? or is my teacher mistaken..
And how is NO2 bonded? Nitrogen has 3 available covalent bonds while Oxygen has 2. Is this case similiar to that of CO where co-ordinate covalencies are involved or what? I've tried drawing diagrams for the bonding structure (without co-ordinate covalent bonds) and still haven't found a possible case where N and O can exist as NO2 (Or NO for that matter)... :( woe is me.

Clyde
06-03-2003, 04:55 AM
On my homework, I came across a reference to a molecule with a formulae of XeF4. Is such a molecule possible? or is my teacher mistaken..
And how is NO2 bonded? Nitrogen has 3 available covalent bonds while Oxygen has 2. Is this case similiar to that of CO where co-ordinate covalencies are involved or what? I've tried drawing diagrams for the bonding structure (without co-ordinate covalent bonds) and still haven't found a possible case where N and O can exist as NO2 (Or NO for that matter)... woe is me.


XeF4 is a real molecule, as is NO2, CO, and a whole host of other molecules.

The faff answer is you use dative covalent bonds:

In CO carbon needs 4 and oxygen needs two, they form a double bond by sharing two electrons each giving oxygen its full outer shell and leaving carbon still needing two more, so oxygen lets carbon share two more of its electrons, thats a dative covalent bond.

NO2 you can represent as a one neutral oxygen double bonded and once negative oxygen single bonded to a positive nitrogen. Use normal rules then add an electron to the negative oxygen and remove one from the positive nitrogen.

The real answer is that chances are, almost everything you have been taught about bonding is utter nonsense: All the stuff you have done on ionic bonding (those circle diagrams) is complete nonsense and what you understand of the entire driving force behind chemical reactions - the octet or "full outer shell" rule is not the be all and end all that it is presented as at your level.

Panopticon
06-03-2003, 05:03 AM
Yeah just as I suspected, dative bonds. (Dative bonds are another name for co-ordinate covalent bonds apparently) Seems like that would be the only way those mentioned molecules could exist.


The real answer is that chances are almost everything you have been taught about bonding is utter nonsense: All the stuff you have done on ionic bonding (those circle diagrams) is bogus and what you understand of the entire driving force behind chemical reactions - the octet or "full outer shell" rule is also all lies.
Well, my "chemistry" teacher is an idiot that can't read the periodic table, and is actually a biology teacher which imo shouldn't be considered a science. (and I question his ability in that field too) See, because of that I've taken the initiative to tutor myself on the sciences from text books. Now, what you're saying is the books I'm using are wrong? That's a pretty big statement.

Either way, thanks for confirming my suspicions :)

Clyde
06-03-2003, 05:06 AM
"I've taken the initiative to tutor myself on the sciences from text books. Now, what you're saying is the books I'm using are wrong? That's a pretty big statement."

The way chemistry is taught at pre-undergrad levels is amazingly simplified to such an extent that it's essentially nonsense.

Ok, not all of it, at levels just pre-undergrad (A-Levels in England) its starts getting a bit better.

So yea alot of whats in your books is "wrong" but then the authors know this and wrote them "wrong" deliberately so that they would be easier to understand.

Panopticon
06-03-2003, 05:11 AM
Oh ok I see, point taken.
Yeah, I'm starting to realise alot of stuff is made gibberish for the sake of simplicity, but they do serve as a healthy foundation for deeper concepts that are to come at higher levels of study, simply because the bs learnt before would in most cases require small alterations to suit the current teaching. I see your point.

Well, personally I'm not really a chemistry person anyway, only taking chem cos its a science and I'm naturally good at understanding concepts (well, compared to my ineptitude in English, which here is sadly a compulsory subject thats downright pulling my beautiful marks down :( ) I'm more into physics, but then again, at a high school level they teach physics as its name implies "physics" as general as it comes. We learn the basics of everything. hehe I like rambling.

Fountain
06-03-2003, 10:41 AM
Why is biology not a science?

Or did you mean like at school level or something. It is kinda important subject and may lead to ppl studying medicine/chemistry etc etc. Or is it just the 'word' biology you dont believe is a science?

ZerOrDie
06-03-2003, 12:37 PM
Originally posted by Panopticon
Oh ok I see, point taken.
Yeah, I'm starting to realise alot of stuff is made gibberish for the sake of simplicity, but they do serve as a healthy foundation for deeper concepts that are to come at higher levels of study, simply because the bs learnt before would in most cases require small alterations to suit the current teaching. I see your point.

Well, personally I'm not really a chemistry person anyway, only taking chem cos its a science and I'm naturally good at understanding concepts (well, compared to my ineptitude in English, which here is sadly a compulsory subject thats downright pulling my beautiful marks down :( ) I'm more into physics, but then again, at a high school level they teach physics as its name implies "physics" as general as it comes. We learn the basics of everything. hehe I like rambling.

no no you dont understand... what you learn is completly useless and has not been used since the 1800's in most cases... and most of it is completly irrelevant to the current theories...

Ken Fitlike
06-03-2003, 12:51 PM
>>I've taken the initiative to tutor myself on the sciences from text books<<

Perhaps an introduction to Molecular Orbital theory may be of interest:

http://www.chm.davidson.edu/ChemistryApplets/MolecularOrbitals/index.html

http://www.ch.ic.ac.uk/vchemlib/course/mo_theory/main.html

http://www.chem.qmul.ac.uk/software/download/mo/

A little group theory (molecular symmetry) is always useful too:

http://www.chem.wm.edu/courses/chem402/hand.html

http://www.science.siu.edu/chemistry/tyrrell/group_theory/sym1.html

>>...not been used since the 1800's in most cases...<<

Was it as long ago as that? Just seems like yesterday... :p ;)

Panopticon
06-04-2003, 12:12 AM
Thanks for the feedback ppl, really helps.


Why is biology not a science?

Well personally I have nothing against the study as a science itself, I guess I wasn't thinking straight in my haste when I typed. My opinion though is that people (in my school anyway) that take biology ........ me off cos you cud just tell by their behaviour that hey have no passion for the sciences, and merely taking it cos they are (most, no, vast majority) mindless mediocre drones void of individual thought that go by the cliche that "doctors get paid alot and i like money, therefore i'll take biology!".

Brian
06-04-2003, 11:12 AM
Originally posted by Clyde
"I've taken the initiative to tutor myself on the sciences from text books. Now, what you're saying is the books I'm using are wrong? That's a pretty big statement."

The way chemistry is taught at pre-undergrad levels is amazingly simplified to such an extent that it's essentially nonsense.


Holy $$$$!

I'm ........ed off now. Everything I've been taught is bull$$$$? That is $$$$ing gay. Means I'll have to relearn it all at $$$$ing chemistry A Level. If people weren't so $$$$ing retarded, maybe they'd teach us the real deal rather than a bunch of lies. 8 electrons in the outer shell my ass.

Ken Fitlike
06-04-2003, 11:42 AM
>>Everything I've been taught is bull$$$$?<<

As Clyde has pointed out it's a 'simplified' version ie texts are "...wrong" but then the authors know this and wrote them "wrong" deliberately..."

There are historical and utilitarian reasons for this - for many practical purposes this 'simplified' or conventional approach works perfectly well and so a 'it's good enough to get the job done' attitude is taken. For example, consider what you have learned in Chemistry so far: you are able to predict with some precision and certainty the paths, states and outcomes of many reactions using these 'older' models.

Here's an analogy: consider the expressions "the sun comes up" or "sunrise". These expressions exist for historical reasons, before understanding of the motions of Earth and Sun were properly understood. We retain - and understand - these expressions because they 'seem' to be true; they have sufficient utility and practicality in our everyday lives so that there is no need, at that level of understanding, to alter them or their use even though we know that they are actually false statements.

Anyway, if you think that's bad, consider the plight of electronic engineers who, by convention and for pretty much the same historical reasons, use positive current flow. ;)

Brian
06-04-2003, 05:28 PM
Yeah, but they could have at least told us, "this isn't true, but..."

Speedy5
06-04-2003, 05:36 PM
Well I'm in tenth grade and my honors chemistry teacher was ACTUALLY a chemist! He worked on lasers. Anyways, we were taught things beyond the textbook and things that other chemistry teachers don't know how to do.

But in bonding, we were taught about the s, p blocks, hybrid orbitals, exceptions to the octet rule, and all this crazy stuff. Seems really real and I understand why many of these molecules bond and how and which "slots" are open for more bonds.

So it all depends on your teacher.

ZerOrDie
06-04-2003, 10:33 PM
Originally posted by Speedy5
Well I'm in tenth grade and my honors chemistry teacher was ACTUALLY a chemist! He worked on lasers. Anyways, we were taught things beyond the textbook and things that other chemistry teachers don't know how to do.

But in bonding, we were taught about the s, p blocks, hybrid orbitals, exceptions to the octet rule, and all this crazy stuff. Seems really real and I understand why many of these molecules bond and how and which "slots" are open for more bonds.

So it all depends on your teacher.

:rolleyes: yeah a laser! that is proof he is a chemist :rolleyes: that would actually have more to do with physics...

and trust me the stuff you learnt was not what is currently used by chemists...

not to mention the whole high school level bonding theory is bogus...

Zach L.
06-04-2003, 10:40 PM
Originally posted by ZerOrDie
and trust me the stuff you learnt was not what is currently used by chemists...

not to mention the whole high school level bonding theory is bogus...

True true, but then again, so many things are like that. Take physics as an example. Just about every school starts out teaching Newtonian physics, as opposed to more recent theories such as Relativity.

ygfperson
06-04-2003, 10:46 PM
Originally posted by Panopticon
Thanks for the feedback ppl, really helps.



Well personally I have nothing against the study as a science itself, I guess I wasn't thinking straight in my haste when I typed. My opinion though is that people (in my school anyway) that take biology ........ me off cos you cud just tell by their behaviour that hey have no passion for the sciences, and merely taking it cos they are (most, no, vast majority) mindless mediocre drones void of individual thought that go by the cliche that "doctors get paid alot and i like money, therefore i'll take biology!".
While we're at it, let's stereotype nurses for not being smart enough or ambituous enough to become doctors. Or pilots for being too cowardly to become regular infantry.

Biology is definitely a science, and a hard one at that. It employs the scientific principle over and over again, same as Chemistry and Physics.

Zach L.
06-04-2003, 10:50 PM
Biology is a science, though the way it is taught in many schools, it barely qualifies. A lot of the 'school biology' is just memorization, and doesn't really require much actual thinking.

SMurf
06-04-2003, 11:41 PM
Pre-advanced level science is much like The Matrix. You get told relatively simple concepts which work under laboratory conditions, the sun shines, people are happy.

Then at the start of A-Level/Scottish Highers or non-British equivalent you meet up with this bald guy (Played by Laurence Fishburne) who offers you some pills. Suddenly you find out that everything they told you was a lie and you basically have to re-learn science while evading psycotic kung-fu English teachers who are under the impression you don't know the language.

At one point you learn that the Government is going to let education standards slide by keeping more of this "false science" in advanced level, and then it's up to you to save humanity.

You'll get what I'm on about soon :D

Panopticon
06-05-2003, 02:37 AM
Yeah... Biology is a science. What I meant was that in my haste I chucked a freudian slip and said bio wasn't a science instead of making a direct attack on dumb jocks in my school.

And about the matrix analogy... you just ruined my day.

and about this so called octet rule... what is it?

edit::
And about the electron configurations of elements... I cannot explain why there are inconsistencies in the pattern progression (i forgot specifically which elements break the pattern but e.g. one element wud prolly be like 2,8,13,2 and the next wud be 2,8,15,1 instead of the expected 2,8,14,2.. [these configs are arbitrary] ) Is this a direct consequence of the inane models used in highschools?
Likewise with why transition metals will have inconsistent valencies dependant on what it is reacting with.

Clyde
06-05-2003, 10:06 AM
and about this so called octet rule... what is it?

It goes something along the lines of: "The reason chemical reactions occur is so that each atom is able to get a full outer shell of electrons". Given that all the "shells" other than the first one supposedly contain 8 electrons its called the octet rule. From your query below it seems that perhaps it has not been emphasised in your course.



And about the electron configurations of elements... I cannot explain why there are inconsistencies in the pattern progression (i forgot specifically which elements break the pattern but e.g. one element wud prolly be like 2,8,13,2 and the next wud be 2,8,15,1 instead of the expected 2,8,14,2.. [these configs are arbitrary] ) Is this a direct consequence of the inane models used in highschools?


I think what you are talking about is the change in energy between the 4s and the 3d which occurs in the transition elements.

Lets take Nickel, its electronic structure is

1s2 2s2 2p6 3s2 3p6 4s0 3d10

Whereas its expected to be 4s2 3d8

Basically the 4s and the 3d are very similar in energy and due to orbital shielding effects the 4s ends up feeling less effective nuclear charge and hence becomes higher in energy than the 3d in certain situations.

So to answer your question, yes its due to inane models, (though I covered this particular topic pre-undergrad) as soon as you start talking about orbitals and their effects on shielding and nuclear charge it make more sense (although you don't start getting any explanations for why orbitals are the way they are untill a much higher level).



Likewise with why transition metals will have inconsistent valencies dependant on what it is reacting with."


The differing valencies of transition metals can't really be understood untill you start covering molecular orbital theory, crystal field theory, and the effects of ligands with regards to stabilising charges.

golfinguy4
06-05-2003, 01:03 PM
Originally posted by Clyde

The differing valencies of transition metals can't really be understood untill you start covering molecular orbital theory, crystal field theory, and the effects of ligands with regards to stabilising charges.

:me's confused now:

Clyde, are you a chemist? Or did you just take some advanced chem courses?

Clyde
06-05-2003, 03:10 PM
I'm on a chemistry degree, next year is my final year.

golfinguy4
06-05-2003, 03:36 PM
Good. If not, you would just be insanely smart.

Panopticon
06-06-2003, 12:12 AM
>> From your query below it seems that perhaps it has not been emphasised in your course

No, my course basically revolves around this principle. Except we don't call it that.

And damn.. i don't understand your electron config notation, with the letters between numbers :rolleyes: i feel so primitive. I bet they have something to do with your mentioned modern theories. I am interested in them and would investigate them further but because I am about a year and a half away from my final exams (equivalent to the american SAT or ACT or whatever, the university entrance one) I'm highly preoccupied by all this assorted gibberish they throw at me.

But again, thanks Clyde, you've broadened my understanding a lil, now that I know the stuff I've been learning are all lies. :)