So i read that XeF5 does not exist as it is compound with odd no of electrons. ClO2 being another odd no of electron compound exists. How? Is there anything i am missing here?
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$\begingroup$ Really good link here should help chem.libretexts.org/Courses/Rutgers_University/…. There is a free radical section on the website $\endgroup$– ChemLover68Commented Aug 23 at 7:37
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$\begingroup$ chemistry.stackexchange.com/questions/98942/… $\endgroup$– MithoronCommented Aug 23 at 21:39
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$\begingroup$ What is there to miss? Most radicals are extremally reactive. XeF6 is very reactive by itself and you'd want to make a radical of it? $\endgroup$– MithoronCommented Aug 23 at 21:42
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$\begingroup$ Note that the common triplet dioxygen $\ce{O2}$ is a a "double-odd electron molecule". Kinetic stability depends on the reaction path. Disproporcionation is for XeF5 much easier than for $\ce{ClO2}$ or $\ce{NO2}$. $\endgroup$– PoutnikCommented Aug 24 at 12:28
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$\begingroup$ Also see: chemistry.stackexchange.com/questions/39001/… $\endgroup$– Nilay GhoshCommented Sep 7 at 6:49
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2 Answers
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In general, species with an odd number of electrons are unstable because they have an unpaired electron and usually can't satisfy the octet rule. ClO2 kind of exists, but it is unstable and decomposes into Cl2 and O2. XeF5 doesn't exist because compounds with noble gases are very rare (relative to compounds with oxygen and chlorine) since noble gases already have a full octet. Being a radical just makes XeF5 even more unlikely to exist.
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$\begingroup$ "species with an odd number of electrons are unstable" - what does this mean? Many, many odd electron species if isolated will sit there perfectly happily. I think you mean "highly reactive". That said given the number of exceptions to the octet rule, e.g. all of transition metal chemistry, I don't think this a great answer. $\endgroup$– Ian BushCommented Aug 24 at 7:06
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$\begingroup$ Unstable vs. highly reactive is a distinction between thermodynamics and kinetics, yes, but I don't think the distinction particularly matters here. If I say a) existing and b) not tending to exist for very long in standard conditions constitutes instability, then the principal reason why something would "not exist very long" is that it undergoes a reaction. Typically the "octet rule" is used when discussing main group elements. Yes, transition metals do not satisfy the octet rule, but we're not talking about transition metals here. $\endgroup$– unstableCommented Aug 24 at 7:49
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$\begingroup$ It is good to distinguish thermodynamic and kinetic stability. Diamonds are instable in the former, but stable in the letter sense. $\endgroup$– PoutnikCommented Aug 24 at 16:19
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If $\ce{ClO2, NO}$ would make a dimer, the new bond would be a non-bonding molecular orbital. As it is non bonding, the bond would soon get dissociated at usual temperatures. For example, $\ce{NO}$ forms a dimer at very low temperatures, much below $0$°C. It can also be stated for $\ce{NO2}$ which makes the dimer $\ce{N2O4}$ with a measurable equilibrium constant near $0$°C.
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$\begingroup$ I sort of agree with this except the point of the question is that $XeF_5$ does not exist (for any reasonable length of time) in isolation, while all the others you mention do - so I would suggest cutting $XeF_5$ from the list, or trying to explain why it is different from the other species you mention. $\endgroup$– Ian BushCommented Aug 24 at 14:47
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$\begingroup$ Ian Bush. Thank you for your remark. When writing my text, I had not thought of the xenon pentafluoride, that I had never seen before. I was mainly thinking of chlorine and nitrogen oxides. So I will edit my text and remove the xenon fluoride. $\endgroup$– MauriceCommented Aug 24 at 16:11