| Pages:
1
..
4
5
6 |
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Ok I'm struggling here and the more I am reading the more I come to see that something is wrong with this stupid octet rule. Standard teaching - no
shell can have more than 8 electrons, But something is wrong. I will take one example from the periodic table - Titanium. 1s2 2s2 2p6 3s2 3p6 4s2
3d2 (or Ar 3d, see I'm getting there ) People always draw the nucleus, then
successive concentric rings around the nucleus beginning with 2 and then filling each ring with 8 until we have finished counting. This is so
misleading as to be scrapped surely from all chemistry? Titanium has 10 electrons in the 3rd energy level for example, how can one then place 2
concentric circles of 8 electrons and the final outer circle with 4 electrons? This seems so absurd now. The same applies to practically most of the
elements. Asfar as I see it does not make for very good shorthand, the Lewis dot structures are very good shorthand methods/graphical illustrations
of bonding, but this concentric circle with no more than 8 electrons thing is just baloney. It made sense until I started learning about the the
configurations.
[Edited on 4-2-2015 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Titanium: 1s2 2s2 2p6 3s2 3p6 4s2 3d2 = [Ar] 4s2 3d2
The Octet Rule works very well in a large number of cases.
As regards the drawing of concentric circles with the electrons on it, that's a very old form of representation, abandoned almost completely in modern
text books. Modern concepts/representations take time to percolate through the 'systems'. Have mercy!
Re. Cu(II), simple rules like Hund's Rule do not tell the full story here. Other energies are at play. Am digging right now.
[Edited on 4-2-2015 by blogfast25]
|
|
|
Metacelsus
International Hazard
Posts: 2531
Registered: 26-12-2012
Location: Boston, MA
Member Is Offline
Mood: Double, double, toil and trouble
|
|
Yes, the 8 electron rule is useless for anything with d or f orbitals.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
In the case of Cu(I/II) one energy consideration that may need to be taken into account is the lattice energy of Cu(I/II) ionic compounds.
Have a good look at the Born Haber Cycle:
http://en.wikipedia.org/wiki/Born%E2%80%93Haber_cycle
It describes all the subprocesses involved in 'creating' a binary ionic compound (in the wiki example: LiF), thus allowing to predict the Enthalpy of
Formation of said ionic compound.
Two important energies in that process are the ionisation energy (endoenergetic) of the cation and the lattice energy (exoenergetic) of the crystal
lattice.
In the case of say CuCl2 the ionisation energy of Cu === > Cu<sup>2+</sup> + 2 e<sup>-</sup> is of course higher than for
CuCl.
But the lattice energy of CuCl2 however is significantly higher (more negative) than that of CuCl, because of the higher charge of the
Cu<sup>2+</sup> ion and the higher electrostatic attractive forces associated with that.
Add it all up and the Standard Enthalpy of Formation of CuCl2 is indeed higher than that of CuCl.
CRC 86:
Standard Enthalpy of Formation of CuCl = - 137.2 kJ/mol
Standard Enthalpy of Formation of CuCl<sub>2</sub> = - 220.1 kJ/mol
[Edited on 4-2-2015 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Cheddite cheese: glad that I had not overlooked anything here then, unlike aufbau hunds and pauli rules the octet rule does not seen to be a 'rule'
really.
Blogfast: so back we go to enthalpy and entropy and other things, good, I knew there must be something but just did not know where to look.
.....
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
As regards Azurite, in one of my experiments started well over a month ago, something is "stirring".
Recapping, I prepared Malachite in a pet bottle (for carbonated drinks), from:
2 CuSO4(aq) + 2 Na2CO3(aq) + H2O(l) === > Cu2CO3(OH)2(s) + 2 Na2SO4(aq) + CO2(g)
... by mixing the CuSO4 and Na2CO3 solutions and capping the bottle IMMEDIATELY, well before the reaction could run to completion, thus trapping the
formed CO2. Amounts of reagents were calculated to reach 4 - 5 bar CO2 pressure inside the bottle.
A thick, green slurry formed which on shaking coated the inside of the bottle very evenly.
The hope was that the combination of Malachite, water, CO2 and pressure would then convert the Malachite to Azurite
(Cu<sub>3</sub>(CO<sub>3</sub><sub>2</sub>(OH)<sub>2</sub> as per the reaction
equations outlined higher in this long thread.
This 'coating' has gradually changed over the many weeks, developing what I can only call 'structure'.
And now (just peeked) light blue patches are forming. Far too soon to claim victory but this is very interesting
nonetheless.
Photos will have to wait because I'm still basically bed ridden.
Quote: Originally posted by CHRIS25  | Blogfast: so back we go to enthalpy and entropy and other things, good, I knew there must be something but just did not know where to look.
..... |
The Pauli Exclusion Principle is derived from theory, it's not some arbitrary 'rule of thumb'.
Hund's rule is an observational rule, very useful but not chiselled in granite.
The Octet Rule is a useful rule of thumb that still helps explaining the 'valence' of many elements in simple molecular structures. It has many limits
but don't throw away the baby with the bath water.
[Edited on 4-2-2015 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
....no keep the baby throw away the bath water.
I think you started yours way before me, , mine began on 1 january, green for the first week turned to blue green now without a doubt, but I have now
stuck mine outside where the temp is constantly 0 - 2 c. I also laid the bottle horizontally so that 1/3 of the malachite covered limestone is out of
solution and exposed to nothing but the carbon dioxide and pressure. No idea why, seemed like a logical thing to try to be honest. Looking forward
to your results. Have you had time to plot those figures you mentioned some while ago?
[Edited on 4-2-2015 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
These are the results of the study I was referring to in response to kmno4: off limits for the moment due to that 'broken' computer (a bad crash but
nothing an IT guy can't solve).
My results showed that essentially high CO2 pressure may well prove irrelevant for creating the conditions outlined in that paper on the stability
relations you linked too much higher up. This from a thermodynamical viewpoint but perhaps not from a kinetic viewpoint.
I'll publish a summary here as soon as it's feasible. I'm still crawling the walls with a mixture of pain and nausea right now.
[Edited on 4-2-2015 by blogfast25]
|
|
|
| Pages:
1
..
4
5
6 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
