For example, what is the electronegativity difference for Acetone(CH2O)? Are there two different answers? 0.4 for C & H, and 1.0 for C & O? Which one do you choose?
6 Comments
AlwaysReady1
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Apr 3, 2016, 10:14 PM
I might not understand very well the question but if you are trying to find an electronegativity for a compound to try to assess if it would attract electrons I think there are other factors that would affect this.
I would say that depending on the compound. In the case of CH2O, which would be formaldehyde, you could see that the oxygen has two pairs of electrons available to be donated. Neither H or C would be available for bonding since they have all the bonds necessary to fill the valence shell.
Robo94
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Apr 4, 2016, 10:22 AM
You're trying to apply something from a binary system to a bigger system. I assume you're trying to find the dipole moment of a molecule. In a biatomic molecule, (A bonded to B) you can just say the potential difference is that of A minus that of B. Bigger molecules require a lot more math per atom.
If you're asking because you need homework help its a completely different process than what you're used to. I suggest starting by figure out how to do it with Water, and working your way out from there.
Electronegativity is a concept that is designed for individual elements (individual atoms really), and isn't really applicable to molecules.
What exactly are you trying to use this information for? If you're looking at how electrons will transfer between molecules, there's a little bit more going on - within a molecule, more electronegative elements can pull electrons away from other atoms (this is common in organic molecules, for example, where oxygen often bonds to carbon and will pull some of its electrons away). However, this effect is reduced in longer molecules. It's a more complex system because molecules don't have one constant electronegativity (which you can approximately say is true for atoms), but instead have more localized regions of charge at different locations on the molecule that will react differently.
It sounds to me like your question is about the electronegativity difference between atoms of an acetone molecule. For this, it definitely depends on the two atoms you're looking at, and will not be constant throughout - however, it will also notsimply be the difference you'd calculate from an electronegativity table because of the effects mentioned above.
This was kind of a vague explanation and I'm only an undergrad so take my words with a grain of salt, but feel free to ask me to elaborate.
cheeseborito
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This is wrong.
Electronegativity is by definition the pull an atom has on the electrons in a covalent bond with another atom. So, in reality, an element does not have one standard electronegativity, and its measured electronegativity will vary based on what it is bound to. We can't talk about the electronegativity of one atom in a vacuum.
That isn't to say we can't speak in averages, and for all intents and purposes (Though not technically), the effective electronegativity of an oxygen atom bound to a carbon atom will be more or less the same.
As far as I'm aware, while my definition of electronegativity may not be flawless, the pull of an oxygen atom on the electrons of a carbon atom is not independent of what the carbon is bound to. The effective local charge around the oxygen in acetic acid, for example, would be higher than that of the oxygen in decanoic acid.
The electronegativity thing may have been poor phrasing on my part - I didn't mean individual atoms in a vacuum, but rather individual pairs of atoms relative to one another. An oxygen will always exert the same pull relative to a carbon but the relative difference in local charge will vary because of other atoms exerting a pull - thus the things we typically use electronegativity to understand become more complicated.
Atoms of elements that are nonmetals tend to gain electrons and atoms of metallic elements tend to lose electrons. Metals have few electrons in their valence shells.
By losing those electrons, these metals achieve noble gas configuration and satisfy the octet rule.
Nonmetals that have close to 8 electrons in their valence shells readily accept electrons to achieve noble gas configuration.
An example is the reaction between calcium and oxygen. Calcium is a metal and has 2 valence electrons. Oxygen is a nonmetal and has 6 valence electrons.
Calcium gives up its two valence electrons and oxygen accepts them and an ionic bond is established resulting in the formation of anew compound namely calcium oxide.
Ion exchange chromatography is a chemical process where molecules are separated by affinity to an ion exchange resin. To separate different aminoacids you must use the isoelectric point (That is the pH where the aminoacid will be in its neutral form).
For lysine, PI is:
9,8
For arginine:
10,75
At pH = 9,8 lysine will be in its neutral form and will not be retain in the column but arginine will be in +1 charge being retained by the ion exchange resin.
Thus, <em>pH 9,8 is likely to work best for this separation</em>
