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> but I can't find any canonical reference as to that.
[Look harder][1] ;-)
It seems to be that the lone pair has lowest priority.
OK, I can't find any *authoritative* reference to that (I don't have access to the [original paper][2]), but I've got plenty of others:
> In the Cahn-Ingold-Prelog priori... |
> but I can't find any canonical reference as to that.
[Look harder][1] ;-)
It seems to be that the lone pair has lowest priority.
<s>OK, I can't find any *authoritative* reference to that (I don't have access to the [original paper][2]), but I've got plenty of others:</s>
Alright, IUPAC [says][3]:
>Exce... |
can an atom have more than 8 valence electrons? according I have reviewed in chemical texts, the max quantity is 8, but does not explained the why. then if is not possible, why an atom can not have more than 8 valence electrons? thanks in advance. |
can an atom have more than 8 valence electrons? if not, why 8 is the limit? |
Can an atom have more than 8 valence electrons? According to some chemistry textbooks, the maximum number is 8, but they do not explain why. If is not possible, why can't an atom have more than 8 valence electrons? |
Can an atom have more than 8 valence electrons? If not, why 8 is the limit? |
Can an atom have more than 8 valence electrons? According to some chemistry textbooks, the maximum number is 8, but they do not explain why. If it is not possible, why can't an atom have more than 8 valence electrons? |
Chiral molecules tend to absorb one circular polarization of light more than the other. Is this ever used to isolate a particular enantiomer? |
Is circularly polarized light ever used to isolate particular chiralities? |
I'm familiar with the concept of a reaction coordinate from high school chemistry as some generic conformational parameter that all of the intermediate states of a chemical reaction lie upon. Recently, though, I've seen some presentations where chemists presented plots of the free energy with respect to two reaction co... |
What does "reaction coordinate" mean? |
I liked this question because I had never thought much about it. However, it's not such a mistery because the answer is in the [Wikipedia “radical” page][1]:
> Historically, the term radical was also used for **bound parts of the molecule**, especially when they remain unchanged in reactions. These are **now called ... |
While reading [this paper][1] (suggested by @jonsca [here][2]), I came across the following line:
> Surface reconstruction is known to be extremely important for Si, the material of 20th century electronics. However, surface reconstruction has been much less studies for graphite. One of the reasons might be graphit... |
Why is fabrication of ordered graphite substrates difficult? |
While reading [this paper][1] (suggested by @jonsca [here][2]), I came across the following line:
> Surface reconstruction is known to be extremely important for Si, the material of 20th century electronics. However, surface reconstruction has been much less studies for graphite. One of the reasons might be graphit... |
This answer is intended to supplement [Manishearth's earlier answer](http://chemistry.stackexchange.com/a/445/83), rather than compete with it. My objective is to show how octet rules can be helpful even for molecules that contain more than the usual complement of eight electrons in their valence shell.
I call it do... |
Just some while ago i was burning a box of cardboard in my backyard and I saw a very curious phenomenon .
I saw that as the cardboard box started burning it started to curl. up after a while as i came back to check if the fire was out i saw that though the cardboard box wasn't a box any longer but individual sides... |
Most molecules containing nitrogen atoms in trigonal pyramid configuration undergo a relatively fast process of [inversion](http://en.wikipedia.org/wiki/Nitrogen_inversion) at room temperature. On the other hand, the free energy barrier for [phosphines](http://en.wikipedia.org/wiki/Phosphine), [sulfoniums](http://en.wi... |
How come trigonal S and P compounds do not undergo inversion at room temperature? |
Just some while ago I was burning a box of cardboard in my backyard and I saw a very curious phenomenon.
I saw that as the cardboard box started burning it started to curl. Up after a while as I came back to check if the fire was out I saw that though the cardboard box wasn't a box any longer but individual sides/... |
While reading [this paper][1] (suggested by @Janice [here][2]), I came across the following line:
> Surface reconstruction is known to be extremely important for Si, the material of 20th century electronics. However, surface reconstruction has been much less studies for graphite. One of the reasons might be graphit... |
Given two crystal space groups, how can one determine if they are in a group-subgroup relationship? The specific case at hand is **P 21/m 2/m 2/a** (aka **P m m a**, [#51][1]) and **P m m 2** ([#25](http://img.chem.ucl.ac.uk/sgp/large/025az1.htm)), but knowing how to solve this question in a general manner will sure pr... |
Are these two space groups in a group–subgroup relationship? |
According to some chemistry textbooks, the valence shell can only hold eight electrons (except for hydrogen). This is called the "octet rule", and is invoked often.
But, many of the shells have a capacity of more than eight. (2,8,18,32.... are the capacities of successive shells). They are only restricted to eight ... |
Most molecules containing nitrogen atoms in trigonal pyramid configuration undergo a relatively fast process of [inversion](http://en.wikipedia.org/wiki/Nitrogen_inversion) at room temperature. On the other hand, the free energy barrier for [phosphines](http://en.wikipedia.org/wiki/Phosphine), [sulfoniums](http://en.wi... |
Can an atom have more than 8 valence electrons? According to some chemistry textbooks, the maximum number is 8, but they do not explain why. If it is not possible, why can't an atom have more than 8 valence electrons? |
I just bought a heat bag from store and it has special property.
It is made up of transparent plastic bag and transparent unknown liquid inside when sold. There is a tiny circular metal piece in there. If you bend the metal piece, crystalization will occur and release quite a lot of heat. The crystalization will spr... |
What kind of material made up of such heat bag? |
According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained.
So, can an atom have more than 8 valence electrons?
If this is not possible, why can't an atom have more than 8 valence electrons? |
Can an atom have more than 8 valence electrons? If not, why is 8 the limit? |
What material are heat bags made of? |
I just bought a heat bag from store and it has special property.
It is made up of transparent plastic bag and transparent unknown liquid inside when sold. There is a tiny circular metal piece in there. If you bend the metal piece, crystalization will occur and release quite a lot of heat. The crystalization will spr... |
I am currently searching for a portable dehumidifier but notice that most of them come with a indicator that actually using the Blue Silica Gel, which I believe that it may contain Cobalt Chloride.
So, I would like to ask, <br>
(1) if that is the case, would the **portable dehumidifier become a harmful product**?<b... |
Blue Silica Gel more harmful than the orange ones? |
I am currently searching for a portable dehumidifier but notice that most of them come with a indicator that actually using the Blue Silica Gel, which I believe that it may contain Cobalt Chloride.
So, I would like to ask, <br>
(1) if that is the case, would the **portable dehumidifier become a harmful product**?<b... |
Magnetite, $\ce{Fe3O4}$ is able to capture $\ce{As(III)}$ and $\ce{As(V)}$ from drinking water through the following mechanisms.
![enter image description here][1]
Bidentate-binuclear complex
![enter image description here][2]
Monodentate-binuclear complex
(both from [here](http://arsenic.tamu.edu/about/... |
What are the mechanisms for capture of $\ce{As(III)}$ and $\ce{As(V)}$ by magnetite from water? |
Magnetite, $\ce{Fe3O4}$ is able to capture $\ce{As(III)}$ and $\ce{As(V)}$ from drinking water through the following mechanisms.
![enter image description here][1]
Bidentate-binuclear complex
![enter image description here][2]
Monodentate-binuclear complex
(both from [here](http://arsenic.tamu.edu/about/... |
Magnetite, $\ce{Fe3O4}$ is able to capture $\ce{As(III)}$ and $\ce{As(V)}$ from drinking water through the following mechanisms.
![enter image description here][1]
Bidentate-binuclear complex
![enter image description here][2]
Monodentate-binuclear complex
(both from [here](http://arsenic.tamu.edu/about/... |
I've heard some people mention that this or that program isn't "up to date" with respect to the borders used in the Ramachandran plots to classify φ/ψ as being in the most favorable/acceptable/disallowed regions.
How *are* the accepted regions defined? What is the current accepted paper that covers this? |
What are the border definitions in the Ramachandran plot? |
In Cell Culture, DMSO is added to prevent the formation of ice crystals which may lyse the cells. Exactly how does DMSO act as a cyroprotectant? |
How does DMSO serve as a cyroprotectant? |
When mixing two fluids of different composition at constant pressure when no heat can escape, is the enthalpy additive?
If not, how to compute the enthalpy of the mixture resulting from mixing two fluids with given compositin after equilibrium is reestablished? |
Is enthalpy additive in mixing? |
When mixing two fluids of different composition at constant pressure when no heat can escape, is the enthalpy additive?
If not, how to compute the enthalpy of the mixture resulting from mixing two fluids with given composition after equilibrium is re-established? |
As Ali said, unless the mixture is [ideal](http://en.wikipedia.org/wiki/Ideal_solution) the enthalpy of mixing (or excess enthalpy) is not zero. This is the basis for a whole field of thermodynamics (and in particular, statistical thermodynamics): **solution theories**. To quote only a few of the most famous ones:
-... |
Portable dehumidifier require consumer to plug into a outlet to "re-generate" its crystal so that the indicator will change from pink color to its original blue color. However, I notice that there is usually a color-less gas (or smell - as it smell differently from the surrounding air).
So, is the gas (or smell) fro... |
Is the gas (or smell) that come out from a portable dehumidifier safe? |
Can you explain what the crystal is? Based on the common colors you describe and the "Regeneration" I would think that the "crystal" you are describing is just a basic Desiccant (like a silica gel, its hygroscopic, it absorbs water). Most desiccants are pretty(never heard of any issues with common ones used in consumer... |
A portable dehumidifier requires the consumer to plug it into an outlet to regenerate its crystal. When the crystal is thus "regenerated", the indicator will change from pink color to its original blue color. However, I noticed that there is usually a colorless gas (or smell - it smells differently from the surrounding... |
In cell culture, dimethylsulfoxide (DMSO) is added to prevent the formation of ice crystals which may lyse the cells. Exactly how does dimethylsulfoxide act as a cryoprotectant? |
How does dimethylsulfoxide serve as a cryoprotectant? |
What software does the PDB used to generate these "cel-shaded" protein models with outlines around foreground atoms?
 |
What software is used to generate the PDB molecule of the month images? |
[Molprobity](http://kinemage.biochem.duke.edu) and some other protein structure validation tools report a *Cβ deviation* statistic and offer plots for it (example below). Apparently if the Cβ is greater than 0.25 Å, some attention should be given to the residue.
The statistic is given in units of an... |
What is Cβ (C-beta) deviation? |
Can you explain what the crystal is? Based on the common colors you describe and the "Regeneration" I would think that the "crystal" you are describing is just a basic Desiccant (like a silica gel, it's hygroscopic, it absorbs water). Most desiccants are pretty harmless (never heard of any issues with common ones used ... |
Is the smell coming out from a portable dehumidifier safe? |
These illustrations are by [David Goodsell][1], and carry his famous look. Whilst I was not able to determine what specific software he uses, [this page][2] suggests that he probably creates his illustrations as a composite of renders and that the outlines and depth cueing are achieved by running a 'find edges' filter ... |
These illustrations are by [David Goodsell][1], and carry his famous look. Whilst I was not able to determine what specific software he uses, [this page][2] suggests that he probably creates his illustrations as a composite of renders and that the outlines and depth cueing are achieved by running a 'find edges' filter ... |
These illustrations are by [David Goodsell][1], and carry his famous look. Whilst I was not able to determine what specific software he uses, [this page][2] suggests that he probably creates his illustrations as a composite of renders and that the outlines and depth cueing are achieved by running a 'find edges' filter ... |
I know that $H^+$ is not possible in water and it is present as $H_3O^+$ . But later on i come to know that even $H_3O^+$ is not possible and that it is present as $H_9O_4^+$
Why does this happen? what give that compound so much stability that is not present in $H_3O^+$ or $H+$ ? |
I know that H<sup>+</sup> is not possible in water and it is present as H<sub>3</sub>O<sup>+</sup>. But later on I come to know that even H<sub>3</sub>O<sup>+</sup> is not possible and that it is present as H<sub>9</sub>O<sub>4</sub><sup>+</sup>.
Why does this happen? What give that compound so much stability that is ... |
I think that for this type of question a bit of context as to why you are asking the question, would be useful.
If for instance you are in an Intro Chem class I would say the following:
**All chemical systems tend towards their most stable state (in the absence of external energy being applied).**
$H^+$ is j... |
I think that for this type of question a bit of context as to why you are asking the question, would be useful.
If for instance you are in an Intro Chem class I would say the following:
**All chemical systems tend towards their most stable state (in the absence of external energy being applied).**
$H^+$ is j... |
What software does the PDB use to generate these "cel-shaded" protein models with outlines around foreground atoms?
 |
I think that for this type of question a bit of context as to why you are asking the question, would be useful.
If for instance you are in an Intro Chem class I would say the following:
**All chemical systems tend towards their most stable state (in the absence of external energy being applied).**
$H^+$ is j... |
[Molprobity](http://kinemage.biochem.duke.edu) and some other protein structure validation tools report a *Cβ deviation* statistic and offer plots for it (example below). Apparently if the Cβ is greater than 0.25 Å, some attention should be given to the residue.
The statistic is given in units of an... |
Assume a cubic diamond crystal with hydrogen-terminated surface bonds. The terminating hydrogen atoms will form pairs that are geometrically close together in alternating diagonal pairs (think of the rectangles on corrugated walking steel).
Next, picture a formaldehyde molecule being pushed oxygen-first into one of ... |
Is it possible that diamond can be grown from aqueous solutions? |
Are there endothermic dissolution reactions? |
Why is calcium fluoride insoluble? NaCl is soluble, but CaF2 is not. Why is this? |
Why is calcium fluoride insoluble? |
Why is calcium fluoride insoluble? $\ce{NaCl}$ is soluble, but $\ce{CaF2}$ is not. Why is this? |
It's possible to select a perfluorinated hydrocarbon that is immiscible in another organic solvent, forming a distinct phase boundary. Such systems may become miscible at elevated temperature which is exploited in the design of some catalytic processes<sup>1</sup>.
Why is it that many fluorous solvents are immiscibl... |
Why do biphasic systems of fluorous and organic solvents form? |
It seems from a brief search of the literature that 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) is a prototypical room temperature ionic liquid (RTIL) that has been studied extensively. However, numerous -- almost limitless -- combinations of cations and anions that give rise to ionic liquids are possible.... |
Why is 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) often considered a prototypical room temperature ionic liquid? |
What is the specific heat capacity of *liquid* iron? The online handbook I've been using only lists specific heat for the solid and gaseous states. Is this a known property and I'm just looking in the wrong place, or is there a reason specific heat isn't listed anywhere for the liquid state?
I only found one refer... |
Specific heat of liquid iron? |
Does *liquid* iron have a constant specific heat capacity? Everywhere I've looked (save one sourceless online reference to Cp = 611 J/kgK [here][1]), I find no value listed for liquid iron. Is this because the heat capacity is temperature-dependent? Or is this related to a measurement problem? Or does an accepted c... |
I am not a chemicist, I hope I will be enough specific.
Suppose there are two chemical species A, B, with properties:
- at temperature $t<T_r$, no reaction occurs between A, B (in any combination),
- at $t\ge T_r$, A interacts with itself to create $A^2$, B reacts with itself to create $B^2$, and A, B are reacti... |
I am not a chemicist, I hope I will be enough specific.
Suppose there are two chemical species A, B, with properties:
- at temperature $t<T_r$, no reaction occurs between A, B (in any combination),
- at $t\ge T_r$, A interacts with itself to create $A^2$, B reacts with itself to create $B^2$, and A, B are reacti... |
I am not a chemicist, I hope I will be enough specific.
Suppose there are two chemical species A, B, with properties:
- at temperature $t<T_r$, no reaction occurs between A, B (in any combination),
- at $t\ge T_r$, A interacts with itself to create A<sub>2</sub>, B reacts with itself to create B<sub>2</sub>, and... |
Does *liquid* iron have a constant specific heat capacity? Everywhere I've looked (save one sourceless online reference to $C_p$ = 611 J.kg<sup>–1</sup>.K<sup>–1</sup> [here][1]), I find no value listed for liquid iron. Is this because the heat capacity is temperature-dependent? Or is this related to a measurement p... |
Is the specific heat of liquid iron constant? |
Heat capacities are usually dependent on temperature except for ideal gases. You will generally find the values tabulated at specific temperature and pressure values. For instances for which one is interested in heat capacity as a function of temperature, this is usually approximated through a regression equation. The ... |
Okay, let's answer bit by bit:
- Measurement of heat capacity of liquids: this isn't particularly hard to do, and in fact it's much easier to obtain $C_p$ experimentally than $C_V$… however, once you know one, the other can be determined from it and some other thermodynamic properties. Different types of calorimeter... |
I am not a chemicist, I hope I will be enough specific.
Suppose there are two chemical species A, B, with properties:
- at temperature $t<T_r$, no reaction occurs between A, B (in any combination),
- at $t\ge T_r$, A interacts with itself to create A<sub>2</sub>, B reacts with itself to create B<sub>2</sub>, and... |
Heat capacities are usually dependent on temperature except for ideal gases. You will generally find the values tabulated at specific temperature and pressure values. For instances for which one is interested in heat capacity as a function of temperature, this is usually approximated through a regression equation. The ... |
This is a very good question. These compounds have been studied for long enough that most people working with them "know" the answers to these questions, but the answers are buried in physical chemistry articles from 20 or more years ago. The imidazolium tetrafluoroborate salts are popular RTILs because 1) they have th... |
Fluorous solvents have the odd property of being both hydrophobic and lipophobic ([Ref][1]) and thus are not miscible with either aqueous or many organic solvents as you've noted. Fluorine, as the most electronegative element, does odd things to a molecule (and is often used in pharmaceutical compounds just because of ... |
Fluorous solvents have the odd property of being both hydrophobic and lipophobic ([Ref][1]) and thus are not miscible with either aqueous or many organic solvents as you've noted. Fluorine, as the most electronegative element, does odd things to a molecule (and is often used in pharmaceutical compounds just because of ... |
Can someone explain the nomenclature of 7-amino-4-methylcoumarin, pictured below ([from the Sigma-Aldrich website][1])?
![enter image description here][2]
The alpha-carbons of the methyl- and amino-groups here are separated by a minimum of three C's, whereas the numbers 4 and 7 are separated by two digits. What am ... |
*(Assuming this is homework or self-education which should be treated homeworky).*
> 1) why we are not adding the contribution of water to the H3O+ ions
1. Write down the dissociation constant equation with and without $\ce{H2O}$.
What changes?
2. Can you find a formulation of the dissociation constant where ... |
Ok, a little wierd one:
In the title I am refering to silver spoons, which, when used to consume milk products (like yogurt), get a wierd taste. It could be described as umami/meaty, a little bit like onions. I came to the cunclusion that it must be the silver, because this taste is never observed when using steel s... |
While trying to understand the solution of a problem given in my text book, I realized I'm having some difficulty with the solution. The problem is as folows:
The ionization constant of HF is $3.2 \times 10^{-4}$. Calculate the degree of dissociation of HF in its 0.02 solution.Calculate the concentration of all spec... |
Turbostratic graphite is graphite in which there is quenched rotational disalignment between adjacent graphene sheets, i.e. one sheet is rotated with respect to its neighbor. I suppose this could be considered a crystallographic defect of sorts. How do these turbostratic layers form, and can they possess long range ord... |
While trying to understand the solution of a problem given in my text book, I realized I'm having some difficulty with the solution. The problem is as folows:
The ionization constant of HF is $3.2 \times 10^{-4}$. Calculate the degree of dissociation of HF in its 0.02 solution. Calculate the concentration of all spe... |
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