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Thread: Mr. Non-Polar

  1. #1 Mr. Non-Polar 
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    OK so water is a polar molecule. The oxygen has a stronger hold on the electrons than the hydrogen does, so therefore the oxygen is a little negative and the hydrogen is a little positive. I have two questions. (My question mark key is broken so I'm using three dots instead).

    Do all polar molecules have slightly positive and slightly negative parts...

    Does the oxygen have a stronger hold on the electrons because it has a larger nucleus (more protons) than hydrogen...

    How can they prove that the electrons are more strongly attracted to the oxygen. Have they observed it or is it just hypothetical...

    I know I sound stupid, but I'm trying to learn and go beyond what my science teacher teaches me (which isn't a lot).


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    I know exactly what your talking about... my teacher doesn't go into much detail either. But our current unit is on this exactly. I don't know the exact case for H2O but this is how it generally works:

    To figure out if a bond is polar you need to find dEN, change in electronegativity. This can be found on a periodic table. H has EN of 2.2 while O has EN of 3.44. 3.44 - 2.2=1.22.

    Generally you can follow this rule: if dEN < 0.5 the bond is non-polar, if it is between 0.5 and 1.7, it is polar and > 1.7 is ionic. 1.2 is in the middle range and the bond should be polar.

    In order to find out whether the molecule is polar or non-polar you need to find it's vsepr shape. In the case of H2O it is "bent" or "angular". That shape is polar, not non-polar as you said.

    Onto your 2 questions...

    1. Polar molecules have slightly negative and slightly positive ends. I would imagine non-polar to have too, but I think it is negligible.

    2. No, oxygen has a stronger hold because it has a higher electronegativity than hydrogen. I don't know how electronegativity is calculated, but I think it has something to do with the relation between atomic radii and number of protons. Electronegativity is strongest at the top right of the periodic table and lowest at the bottom left.

    Hope this helps.


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    Good job shawngoldw, I don't have too much to say now... Just to give a little more explaination on electronegativity... The most (I'm going to abbreviate it from here on) electronegative element is fluorine, with oxygen being second most. You were right about the elements with more EN being in the upper right of the periodic table, because this is where they have the most protons (positive charge to attract the negative charge of electrons), yet have the fewest electron shells. An element that has more protons, say bromine, has less EN because of its added electron shells, which create distance between the nucleus and the bonding electrons. There's also electron shielding occuring, which shields outer electrons from the attractive power of the nucleus, effectively lowering EN. EN isn't really measured in any way, it's really just determined by comparison of the attractive power of various elements. Fluorine is more 'attractive' than oxygen, so they gave it a higher EN, but the number 3.98 doesn't really mean much, except that it's higher than 3.44. Hope that helped you understand EN a bit better.
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    Thanks a lot, both of you. shawngoldw notice that I did change the term in my post from non-polar to polar because I realized that I had written the wrong one. I did know that water was a polar molecule.
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    I believe the answer to why oxygen is more negatively charged is not about electronegativity, but rather that its nucleus is many many times larger than the hydrogens. A hydrogen is one proton big, while oxygen has 8 protons and 8 nuetrons. Physically the electron would have to spend more time around the oxygen than the hydrogen. The oxygen has no stronger hold than the hydrogen, its just bigger. That would be the biggest cause of its polarity. I would also like to comment on the fact that there are no definite charges, scientists use positive and negative as arbitrary names. I hope I helped. =)
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    No worries P-Manator. Size is a factor, but I don't think it's the main one. In a Fr-Cl bond, if they would bond, which I think they would, The electron would spend more time near Cl although Fr is bigger.
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    =P I just want to point out, incase your not aware, and i'm not intending this to sound arrogant but EN simply means how much an atom wishes to bond with another atom. Since Cl has 7 valence electrons it only needs one more for a complete outer shell. That makes it very eager to get another electron. Now i believe what your referring to is a by product of this effect. It varies on how strong the bond is. It would be found only in covelent bonds, not ionic. So Cl and Fr would not fall into that category. I would imgaine that Fr would bond with Cl, because of Cl EN. All atoms wish to become stable. So the closer they are the more likely and stronger the force will be that will allow that bond to happen. Cl and Fr would not be a polar molecule because its not a covelent bond, It would be considered an ion, if i'm not mistaken. They wouldn't share it, Fr would give up its electron to Cl. I did a little more research into it, EN does have a small part, but it does come down to how big each atom is.

    =) I only mean to help you understand, i'm not here to start arguments. If I am wrong could you please link me to some good sites, i'm always eager to learn new things
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    not trying to start an argument either . Is EN not the strength of the electric field around the atom?

    I know Fr-Cl would be ionic, that would be due to dEN being greater than 1.7.

    I'm saying that size is important but not the only factor. As you move across a period, electronegativity goes up because the atom has more protons, which causes the atom to have a lower atomic radii. But as you move down a group, the atom gets quite a bit larger, yet EN goes down. I have to go but I'll try to find a site later.

    Here,
    as always, WIKIPEDIA!!! http://en.wikipedia.org/wiki/Electronegativity
    http://www.chemguide.co.uk/atoms/bon...lectroneg.html
    Enjoy!
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    Quote Originally Posted by Tony John C
    EN simply means how much an atom wishes to bond with another atom.
    That's not EN. That's called electron affinity. There's a difference. The element with the highest electron affinity is not fluorine (which of course has the highest EN), but chlorine.
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    Quote Originally Posted by Chemboy
    Quote Originally Posted by Tony John C
    EN simply means how much an atom wishes to bond with another atom.
    That's not EN. That's called electron affinity. There's a difference. The element with the highest electron affinity is not fluorine (which of course has the highest EN), but chlorine.

    Umm no. :P EN means exactly what I said. Electron affinity is simply how much energy is released from the ionic bonding.

    I'm actually getting conflictiong answers, from my chem teacher, and my bio professor. It is starting to bug me. For science being so logical, its hard sometimes to find consistency
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    Here is the definition of electron affinity and electronegativity in my notes. As I said before, this is the exact unit we're doing now.

    Electron Affinity: The change in energy that accompanies the addition of an electron to an atom in the gasseous state.

    Electronegativity: The degree of attraction an atom has for a shared pair of electrons.

    Other definitions on that same page are atomic radius, ionization energy, force of attraction and effective nuclear charge. I would imagine them all to be related and have something to do with electron affinity and electronegativity.
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    I'll go with shawngoldw's definitions, so sorry if I offend anyone. Just because he managed to support his definition by pulling it out of his notes. And because Tony John C got conflicting answers from different teachers, I'm not sure if what he's saying is right.
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