Question about free radicals

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Question about free radicals

Postby Biosapien on March 11th, 2015, 3:13 am 

Hi friends,

From the definition of free radical i understand that any atom or a molecule which has a free or unpaired electron in the outermost shell will act as a free radical. If this definition is true then does it mean hydrogen is a free radical. If so how and if not why?. Help me to clarify this piece of information. Thank you.
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Re: Need to clarify

Postby bose on March 14th, 2015, 6:10 pm 

Hydrogen gas exists in the stable molecular form, H2. Obviously this molecule has a pair of valance electrons and therefore is not a free radical. However a hydrogen radical can be formed if the H-H bond is broken. The reaction of hydrogen and chlorine is a photochemical chain reaction involving hydrogen radicals. A chlorine radical breaks the H-H bond, forming HCl and a hydrogen radical. The hydrogen radical then goes on to react with Cl-Cl.

Step 1 Cl2 + light --> 2Cl. Initiation
Step 2 Cl. + H2---> H. + HCl Propagation
Step 3 H. + Cl2 --> HCl + Cl. Propagation
Step 4 H. + Cl. --> HCl Termination

So a hydrogen atom will act as a free radical, but molecular hydrogen gas does not.
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Re: Need to clarrify

Postby Biosapien on March 21st, 2015, 11:15 pm 

hi Bose, thank you for the explanation. you said Hydrogen radicals are produced when there is a break in the H-H bond, what about in case of O-H bond in the water during the formation of hydronium ion. since hydronium ion carries 3 electron does it act as an free radical.
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Re: Need to clarify

Postby BioWizard on March 23rd, 2015, 3:27 pm 

Biosapien

When the O-H bond breaks, it doesn't break equally. That is, the oxygen grabs both electrons (giving it a negative charge, O-), and the H leaves with no electrons (giving it a positive charge, H+). This occurs because of the high electronegativity of oxygen relative to that of hydrogen, which keeps the electrons with the oxygen, and allows the hydrogen atom (which is just a proton at this point) to float around relatively freely. This is why hydrogen bonds are easy to break and hydrogens (protons) are described as being "labile". You can read more about hydrogen bonds here: http://en.wikipedia.org/wiki/Hydrogen_bond

Because of this quality, hydrogen atoms in water can jump from one water molecule to the other. If a water molecules picks up an extra H+, it will become positively charged H3O+. The oxygen in the water molecule is able to pick up the third hydrogen ion (H+) by sharing with it the lone pair of electrons that it has in its valence shell. You can read more about that here: http://en.wikipedia.org/wiki/Hydronium

Let us know if you have any additional questions.
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Re: Question about free radicals

Postby Biosapien on May 1st, 2015, 4:31 pm 

Hi Bio wizard long time no see, here is my question for you. you said in O-H bond the oxygen pull the electron from H and leaving the H as proton due to electro negativity. we all know electrons love to occupy the least energy orbital. my question is why the electron wants to occupy the high energy p orbital of oxygen than less energy s orbital of H when the breaking happens between O-H.
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Re: Question about free radicals

Postby BioWizard on May 1st, 2015, 6:26 pm 

Good question. The electron stays with the oxygen because by doing so, it completes the oxygen's outershell's electronic occupancy (stable). The hydrogen ends up with a completely empty shell, which is more stable than a half filled shell. The small hydrogen nucleus (basically a proton) would have a hard time holding on to two electrons to fill up its outershell's electron occupancy, so it gives up its electron to get an empty orbital instead.

These properties (and others) cause hydrogen to more readily give up its electron, and oxygen to more readily grab that extra electron. The hydrogen is said to be "electropositive", while the oxygen is said to be "electronegative".
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Re: Question about free radicals

Postby Biosapien on May 2nd, 2015, 3:05 pm 

Hi Biowizard , thank you for explaining the fact but I have another question for you from your previous reply. My doubt is will the attraction of electron towards a proton will be higher in H atom or in O atom, because the electron is more closer to the proton of hydrogen rather than proton of oxygen, what you think about the attraction of electron by a proton in relation to distance.
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Re: Question about free radicals

Postby BioWizard on May 2nd, 2015, 4:57 pm 

Electrostatic attraction is affected by distance, true, but it's also affected by charge. The oxygen's nucleus is much more massive with a much bigger positive charge than hydrogen, so oxygen wins. When two electrons are shared between an O and an H in an O-H bond, this causes the electrons to be pulled towards the O. However, the reason the H gives up its electron completely and ionizes to H+ has to do with its own tendency to ionize, not just O's tendency to ionize or pull electrons towards it. In other words, H wants to give up that electron almost just as much as the O wants to take it.
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Re: Question about free radicals

Postby Biosapien on May 3rd, 2015, 3:01 am 

So its mutual beneficial after all. You said proton mass is huge in O when compared to H and this is also one of the reason why electrons are pulled towards the proton. I totally agree with you, imagine this is the situation now the hydrogen has only proton and oxygen has more electron, does this high number electron in O attracts or pulls the proton of the H. My question is if high number of proton can pull the electron from another atom why can,t the high number of electron can pull the proton of an atom which has no electron.
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Re: Question about free radicals

Postby BioWizard on May 3rd, 2015, 7:59 am 

Biosapien » 03 May 2015 02:01 am wrote:My question is if high number of proton can pull the electron from another atom why can,t the high number of electron can pull the proton of an atom which has no electron.


They kind of do. The H+ stays close to the oxygens in water (which are present as H2O or OH-) and jumps from the viscinity of one oxygen atom to the next.
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Re: Question about free radicals

Postby Biosapien on May 3rd, 2015, 10:19 am 

Do you mean the hydrogen stays closer to O because of sharing electron or because of electrons of O atom pulls the proton of the hydrogen towards it. Also I want to clarify wheather the H without any electron has an orbit. Currently I am going through orbital hybridization. I am finding difficulties not in how hybridization occurs but why hybridization occurs.
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Re: Question about free radicals

Postby BioWizard on May 3rd, 2015, 10:26 am 

Biosapien » 03 May 2015 09:19 am wrote:Do you mean the hydrogen stays closer to O because of sharing electron or because of electrons of O atom pulls the proton of the hydrogen towards it.


When they're joined by a bond, it's the former, and when they're ionized, it's the latter. The hydrogen constantly flip flops between the bound and ionized states. What we're describing here is the two extremes of a dynamic equilibrium between two states.

Also I want to clarify wheather the H without any electron has an orbit. Currently I am going through orbital hybridization. I am finding difficulties not in how hybridization occurs but why hybridization occurs.


Why not? A stable occurance happens, by definition. If hybrid orbitals weren't stable, they wouldn't occur. When you calculate the energy of certain hybrid orbitals, you find that it's lower than the energies of their non-hybridized states - and that's "why" they occur. Nature just is.
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Re: Question about free radicals

Postby Biosapien on May 4th, 2015, 2:35 pm 

Thank you Bio wizard, recently I was posted a topic called something from nothing, one of the comment I received is to post the thread into different section does that mean do I have post this under different section, sorry I don't know what you guys call as thread. please help me what should I do with that thank you
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Re: Question about free radicals

Postby BioWizard on May 4th, 2015, 3:35 pm 

You can ask this in the feedback section. A thread is a discussion, like the one we're having here (a thread of posts).
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Re: Question about free radicals

Postby bidwaiaditya on May 6th, 2015, 9:35 am 

hello friends...
does anyone know how to find the valency of a radical?
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Re: Question about free radicals

Postby redwhitechem on June 10th, 2016, 6:42 am 

valency of a radical describe the potential an element or molecule has to bond. You will need Periodic table.
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