Talk:Electron affinity

Electron Affinity

Electron affinity redirects to this page, but should have a page of its own, as electron affinity is the strength an elements has to pull of electrons towards itself. Dreamm 01:56, 4 December 2006 (UTC)

The summary for electron affinity says:

" Group 1 elements (hydrogen, lithium, sodium, potassium, rubidium, caesium, and francium) tend to gain an electron and form -1 anions. "

Actually, Group one elements (Alkali metals) tend to form +1 cations (lose an electron) whereas the halogens (chlorine, fluorine, etc.) tend to form -1 anions (gain an electron). It increases as one moves form left to right in period. Noble gases have electon affinity almost positive or zero and it is highest among all. I don't know why anyone didn't catch that before....

see articles "electronegativity" and "ion" for more information —Preceding unsigned comment added by 207.188.66.137 (talk • contribs)

Nitrogen

Why does Nitrogen have a positive electron affinty? —Preceding unsigned comment added by 67.34.232.130 (talk • contribs)

I think it's because each p orbital has one electron of the same spin in it. This creates a fairly stable configuration so it takes energy to add an electron. It's related to Hund's Rule of Maximum Multiplicity. —Preceding unsigned comment added by Flying Jazz (talk • contribs)

Be wary of the sign of electron affinity: traditionally, it was the energy released on formation of the anion (ie positive number = easily formed anion). The sign convention used in this article is consistent with modern enthalp change conventions for formation of the anion, and hence is the other way round (negative number = easily formed anion).

Yes, to the comment re. nitrogen. But note "The electron affinities in groups 2 and 12 of the periodic table are shown as positive, but should be shown as negative values" in the article. This is untrue. The EA for these elements *are* also positive (and hence impossible to measure directly) because of the great stability of the closed s2 subshell. They are usually quotedf as zero in most older texts, before theoretically calculated values were available.

NB: Group 1 and group 11 have rather negative electronegativities for the same reason (ie group 1 elements *do* have a definite tendency to gain an electron, although they have an even greater tendency to lose one!) AndyChristy 00:45, 20 December 2005 (UTC)

^^^ That should have said 'electron affinities', not 'electronegativities', sorry. Thortveitite (talk) 08:18, 12 May 2009 (UTC)

Lanthanides and actinides

I would like to know if there is any spesific reason for leaving out the Lanthanides and the Actinides from the table of electron affinities? They are also present in the Periodic table. —Preceding unsigned comment added by Loom91 (talk • contribs)

Perhaps nobody has ever measured an electron affinity for the lanthanides or actinides: I've certainly never seen them quoted. Physchim62 (talk) 10:55, 23 December 2006 (UTC)

I found the following measurements, all of them quite recent:

• Lanthanum 45 kJ/mol: Covington, A.M.; Calabrese, D.; Thompson, J.S.; Kvale, T.J. (1998). J. Phys. B: At. Mol. Opt. Phys. 31:L855–60. [1]
• Cerium 92 kJ/mol: Davis, V.T.; Thompson, J.S. (2002). Phys. Rev. Lett. 88:073003. [2]
• Thulium 99 kJ/mol: Davis, V.T.; Thompson, J.S. (2002). Phys. Rev. A 65:010501. [3]
• Lutetium 33 kJ/mol: Davis, V.T.; Thompson, J.S. (2001). J. Phys. B: At. Mol. Opt. Phys. 34:L433–37. [4]

No data available for the other lanthanides, or any actinides. Physchim62 (talk) 22:51, 23 December 2006 (UTC)

Sorry, this is going to be scrappy, as Emacs-23 isn't letting me cut and paste into this buffer. At a conference in 2003 (34'th Meeting of the Division of Atomic, Molecular and Optical Physics of the American Physical Society, Boulder, CO, May 20-24, 2003) VT Davis presented a poster (An Experimental Investigation of Lanthanide Negative Ions) with some more values for Lanthanides (Tb(112)) and 1 update(Ce(96)). In 2002 in J Phys B At. Mol. Opt. Phys. 35 N1 is another paper by VT Davis et al "Measurement of the electron affinity of praseodymium" (93 kJ/mol). In 2005, VT Davis et al in Nucl Instr and Methods B 241, 118 (Sorry missed title) has Neodymium (185 kJ/mol). In 2004, VT Davis et al have "An experimental investigation of the atomic europium anion" in J Phys B: At. Mol. Opt. Phys. 37 1961-1965 has Europium (102 kJ/mol). At an APS meeting in May 2004, VT Davis et al have another poster, "An experimental investigation of the atomic hafnium anion (178 kJ/mol). Sorry, nearest good library is a 5 hour drive from here.

Something called the Physics Handbook has a reasonably complete set of electron affinities, perhaps it is newer data? There is a web page at hem.passagen.se/asystem/PH/default.html Encyclopedia of Earth occasionally has values not found on Wikipedia, including Beryllium (-241 kJ/mol)? UOttawa Astronomy and rcs.org also have more values (for Beryllium, one has +18 the other has -18).

Steve O'Malley and Don Beck at Michigan Technological University are calculating the Lanthanides and Actinides. I looked around Don Beck's web page, and couldn't find anything remotely resembling a summary paper of their calculated values (most of the links are to abstracts or preprints). Some of the numbers looked similar to experimental ones, some looked different. Perhaps someone could look into them? Fortran (talk) 17:24, 29 September 2009 (UTC)

Sign convention

It seems to me that when you convert an atom to an anion that energy is absorbed, not released. - Preceding comment was unsigned.

No, energy is released, in all cases where it can be measured. If this were not the case, the anion would not be stable in the gas phase. Physchim62 (talk) 15:12, 31 July 2007 (UTC)

The article says "It should be noted that the sign convention for E_ea is the opposite to most thermodynamic quantities: a positive electron affinity indicates that energy is released on going from atom to anion." Relatedly, this entry on physicsforums.com specifically addresses the treatment of sign-convention here. That entry also states that Physicists and Chemists tend to use opposite sign-conventions for Electron Affinity, and that "Chemists specify all E_ea values as positive." Are those statements true? Also, it may be helpful to include here some language from the top of the data page for Electron Affinity, which says:

Electron affinity can be defined as either the energy released by adding an electron to a gaseous atom (negative quantity) or the energy required to remove an electron from a gaseous anion (positive quantity). Either convention can be used in practice, but must be consistent (all values should be positive or negative, not mixed.)

I'm still confused about which sign convention is to be used in a given context, but perhaps the info I've included here will help someone with more knowledge of the matter improve the article to mitigate such confusion on the part of other beginning students. - 74.61.38.220 (talk) 06:19, 18 March 2009 (UTC)

All E.A.'s are exothermic?

The current article states "All elements have a positive electron affinity, but older texts mistakenly report that some elements such as inert gases have negative Eea, meaning they would repel electrons. This is not recognized by modern chemists." The texts that I consult, which are fairly conventional, disagree with this statement, which is unsupported by a reference. So I plan to revise this statement. This is pretty basic stuff for beginning students so it would be useful to get it right with real references to real texts. Comments welcome.--Smokefoot 13:08, 22 August 2007 (UTC)

There is some confusion regarding this matter in text books, so I've talked with professional research chemists about this and they all agree that negative electron affinities do not exist. These originate in faulty measurement techniques used by the old experimental chemists and have been subsequently corrected by better measurements. All mono-anions are stable in the gas phase w.r.t. spontaneous electron release. QM calculations also support +ve EAs. Which elements do you believe to have negative EA? Loom91 19:26, 22 August 2007 (UTC)

Thanks, There is no confusion in any texts that I consulted. Ba and some nobel gases are the ones assigned to negative EA's. A reference to a review or a monograph would be handy. The work overturning the negative EA's must either be very new or obscure.--Smokefoot 13:41, 23 August 2007 (UTC)

It is certainly neither. I have at hand a high-school level textbook that clearly says that negative EAs are an outdated concept. Perhaps someone with acess to the latest edition of Cotton-Wilkinson could check out what they have to say on this matter? Loom91 18:42, 25 August 2007 (UTC)

Which book is that? I don't have C&W, but the latest edition of Atkins' Physical Chemistry says something like "the EA of some elements is either very small or may be negative" (paraphrasing). I couldn't find anything relevant in C&W using Amazon's "search inside" feature. --Itub 06:29, 26 August 2007 (UTC)

The one I'm talking about was written by KL Chugh. Are you sure that Atkins explicitly mentions "may be negative"? I've the 7th ed, can you give a reference? Loom91 05:46, 27 August 2007 (UTC)

Page 392: "Electron affinities are also small, and may be negative, when an electron enters an orbital that is far from the nucleus (as in the heavier alkali metal atoms) or is forced by the Pauli principle to occupy a new shell (as in the noble gas atoms)." --Itub 07:31, 27 August 2007 (UTC)

Could you quote exactly what your book says? --Itub 07:33, 27 August 2007 (UTC)

By all means edit as you see fit, this is not an area of expertise to me. I looked at Shriver and Atkins Inorganic Chem and a related text by Miessler and Tarr but these folks may be just reproducing some standard party line. On to other projects... --Smokefoot 12:07, 27 August 2007 (UTC)

Hmm, this article quotes positive values for the EA of alkali metal atoms. Negative values seem unlikely, since species such as natride (Na-) and kallide (K-) do not spontaneously decay into the neutral atom and release an electron. The noble gasses are a more dubious area. Loom91 20:04, 28 August 2007 (UTC)

An interesting article from 1997: [5] (subscription required for full text). It does not say that all EAs are positive, but that negative values for noble gases are "almost certainly not reliable and should be replaced by “≤ 0” unless a reliable source can be quoted". Perhaps there are more recent publications that say that the noble gases are positive too? --Itub 11:24, 24 August 2007 (UTC)

And here's a review from 1994: Josef Kalcher, Alexander F. Sax; Gas Phase Stabilities of Small Anions: Theory and Experiment in Cooperation. Chem. Rev.; 1994; 94; 2291-2318. I haven't read all of it yet, but it says that the noble gases exhibit no electron affinities and that, although the noble gases can form anions, the anions correspond to excited metastable species with lifetimes of the order of milliseconds or as short as femtoseconds. The article uses the term "negative electron affinity" when talking about closed shell systems such as acetylene. --Itub 15:07, 27 August 2007 (UTC)

Of course, compounds can and do have negative electron affinities, that is not disputed. However the term EA generally refers to isolated gas phase atoms of elements, not molecules. Loom91 20:04, 28 August 2007 (UTC)

Noble gases are also closed-shell systems and do not form stable anions according to the review. Doesn't that imply that the EA is negative? From the sources I've found, the only thing I can conclude is that the old negative values for some EAs are considered wrong, not that EAs can't be negative. Also, that the EAs for these elements seem to be hard to measure (presumably because they are negative!), because I haven't found any new values. As I quoted, one of the authors suggests reporting the value as "<= 0". I still don't know exactly what your book says, but I tend to trust specialized reviews and articles in J.Chem.Ed. more than high-school textbooks. Can you provide a solid reference that says that EAs can't be negative? --Itub 05:38, 29 August 2007 (UTC)

Older texts tended to assign negative EAs to a lot more elements than the noble gasses. I've edited the article to make the point that nothing definite is known about the noble gasses, but most other elements upto the fifth row have been measured to have positive EAs. Loom91 07:55, 29 August 2007 (UTC)

There are a few recent determinations of negative EA's in the literature if you hunt about. There is not reason that they cannot occur, but they are difficult to measure. The anion can only be formed by getting the neutral atom into an excited state higher in energy than the final anion. The excited atom then captures its electron and forms the anion briefly before relaxing back down. EA values I have seen show a pretty large spread. Thortveitite (talk) 08:22, 12 May 2009 (UTC)

Additions needed!

More needs to be written about its relation to electron gain enthalpy, which will make things clearer for high school students. Some links too. —Preceding unsigned comment added by 121.247.66.179 (talk) 12:18, 14 October 2007 (UTC)

Question moved from the article

Lvtr asked:

But electron affinity of chlorine is greater than this of Flourine while F is above Cl in the periodic table.On the other hand electron affinty of F is close to this of bromine.Why does this happen????

--Nucleusboy 14:03, 2 November 2007 (UTC) i wanted to ask that too! i thought fluorine would have a higher electron affinity since it is the most reactive halogen. aren't that related? Lichunhon (talk) 12:28, 27 June 2010 (UTC) Probably a measure mistake, because the electronegativity of F is higher than that of Cl which can be compared to electron affinity. I also find it strange because there should be electon affinities for every electron attached to an element, just like they do with the ionization energy. — Preceding unsigned comment added by 86.90.95.123 (talk) 16:46, 18 September 2012 (UTC)

No, the measurements are correct. Fluorine is "too small for it's own good." Crowding an additional electron into the 2p subshell of an F atom releases a little less energy than adding an additional electron into the 3p subshell of Cl. Electronegativity and EA are not exactly the same. Electronegativity is defined as the power of an atom --in a molecule-- to attract electrons to itself. By the way, another manifestation of an F atom being too small for it's own good is that the F-F bond is very weak, among the weakest single bonds in isolable molecules in all of chemistry. Fluorine forms a weak bond to itself but very strong bonds to most other atoms, which is one of the reasons that F2 is the most reactive element. Professor S. H. Strauss, Colorado State Univ.

Data is/Data are

I reverted the change to "Data is" in the leader for the table. My rationale for doing this was that the jury is apparently still out on which of these is the generally correct form, and the phrase "The following data is/are quoted in kJ/mole" appears to refer to the individual values separately, not as a group. Anybody to defend the opposing position?--Nucleusboy (talk) 03:04, 28 November 2007 (UTC)

I prefer the singular, but I don't care that much. An alternative solution would be to use a different word, as in "the following values are quoted..." or "the ionization potentials are quoted...". --Itub (talk) 09:04, 28 November 2007 (UTC)

'Data' is a plural form, and goes with 'are', not 'is'. The singular is 'datum'. Thortveitite (talk) 08:17, 12 May 2009 (UTC)

This article is incorrect ?

From my research and discussion with Dr. Andrew Hemmings at the University of East Anglia, UK. I believe this definition is incorrect.

According to Chemistry 3rd edition by C.E. Housecroft, page 183: "The first electron affinity of an element is minus the internal energy change that accompanies the gain of one electron..."

Hence, how can electron affinity be the loss of an electron, which in my eyes is more ionisation.

If anyone wishes to argue the point with me I would more than be happy to, or point out where I am incorrect?

Regards,

Joshua Dunne, 1st year Biochemistry student. —Preceding unsigned comment added by Joshed100 (talk • contribs) 13:48, 17 October 2008 (UTC)

"minus the internal energy change that accompanies the gain of one electron [by a neutral atom]" is exactly the same as "the internal energy change that accompanies the loss of an electron [from a singly-charged negative ion]". In other words, the ionization energy of the anion (what you could call the "zeroth" ionization energy for the element) is numerically the same as the electron affinity. See the definition given by IUPAC's glossary: [6]. --Itub (talk) 14:15, 17 October 2008 (UTC)

I retract my comment, this definition isn't as clear as I would like, but holds true. - Joshua Dunne

Question

To get one Anion by adding one electron to Chlorine leads to -349 kJ/mole in change of energy.

The electron affinity is defined as EA = -deltaEnergy which then is 349 kJ/mole

This means: when I bring the energy to the other side this means I add 349 kJ/mole on the EA side and have zero on the former -deltaEnergy side. So the euqation looks like this:

689 kJ/mole = 0.

How can they have the same units? It's the same as with resistance and conductivity - but those do not have the same units. Resistance has Ohm and conductivity has Siemens·m⁻1 = Ohm^-1. This means the electron affinity must have the value (kJ/mole)^-1 and not kJ/mole.

91.51.201.217 (talk) 14:20, 4 May 2010 (UTC)

Experiment & Theory

This article can be helped conceptually in two ways. It does not describe the experiment(s) used to measure Ea in atoms and molecules. Next, it would be good to see examples for molecules whose Lowest Unoccupied Molecular Orbital LUMO is either positive or negative. Laburke (talk) 23:20, 11 September 2011 (UTC)

Confusion reigns without arrows

There is an enormous amount of confusion appearing above. Forgive me, if there were any of you who knew that the definition (as of today) is incorrect, then corrected it, but had someone revert it back. According to the IUPAC reference in the article, EA is the energy RELEASED when an electron is attached to an atom. It is not the energy change when an electron is attached. Here's an example. LB (Loan by Bank) is the money RELEASED by the bank (gone from the till). There are "$100 released". If you say "money change", it is ambiguous unless you supply an arrow. This is done two ways 1) saying, "the money in the bank is changed by releasing money", or 2) ΔMoney(bank) = - 100$ = final(money-in-bank) minus initial(money-in-bank). If you say +100LB, the money in the bank goes down by $100 or the bank now has -$100. Saying "Energy change" has as much meaning as "$5 exchange". Am I taking a loan or making a payment?
Suppose the bank manager says, "Well, Jenkins, what did you do today? Well, sir, with Cl there was a (+)349LB but with As there was only a 78LB, and with N there was a -7LB." When you define a LB ( or EA) as $ RELEASED by the bank, you can count what's left in Jenkin's till (-349-78+7$). When you define LB or EA as a change in money, you don't know what's left in Jenkin's till and you get as much confusion as in what was written above. Laburke (talk) 00:09, 21 September 2011 (UTC)

Vertical vs Adiabatic

There should be something on Vertical electron affinity(VEA) and Adiabatic electron affinity(AEA).Smallman12q (talk) 11:38, 24 September 2011 (UTC)

Periodic Trends in Ea

In the section Ea of the Elements the article states: "Eea generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom; a group 7A atom releases more energy than a group 1A atom on gaining an electron because it obtains a filled valence shell and therefore is more stable." Oh boy do I have problems with this. Please accept for this talk page, my use of Ea for Electron Affinity. First it uses the obsolete !!! nomenclature: it is Group 1 and Group 17 OR Group 1 (IA) and Group 17 (VII A) and not the horrible mashup 1A and 7A !!!. Second, attributing cause and effect to Ea and the filling of the "valence shell" needs to be questioned (and I believe tossed out as 'not useful/true'). Do we know what the lowest energy electron configuration is for each atomic anion? I would be surprised if *in the specific case of Group 17* the statement incorrectly assigns the extra electron, but I would be even more surprised if it was in general true that the "valence shell" was the one that was to be expected to be occupied by that electron. Attributing a Periodic trend to a special (not general) circumstance is wrong. Cr has a 4s1 3d5 {4F} ground state so which orbital does the next electron go into: the 4s or the 3d ?? IDK, but certainly can't be known by seeing which Group Cr is in. So is the statement useful if it *seems* to give an explanation but actually the explanation is wrong? The use of the term valence shell is high school level chemistry. Haven't most chemistry students by the end of their Freshman year been taught about subshells, auf bau, and related concepts? Also, by my count across the rows, 25 of the 62 Ea value pairs between adjacent elements violate the claimed trend (thats 40% of them). In my opinion the underlying (quantum mechanical) chemistry does not support the meme and the facts do not support the use of this flawed claim except as the roughest approximation. It is basically only true for the p block. Finally, I'm a bit troubled by the statement that by completing the 7A valence shell releasing more energy is more stable. Obviously given the same initial state a greater energy release is thermodynamically more stable *by definition*, but is it useful? And which of these is "most stable" K(48kJ/mol) Rb(47) Cs (46)? or how about Cr(65) and Co(64)? It seems to me that the assumption that the stability of the anion is proprotional to Ea is wrong. Sure it is true for the (thermodynamically) reversed reaction, but is it true for the anion in its surroundings (and all possible reactions/collisions in may experience)? Is the anion more *chemically* stable compared to a different anion with a completely different electron configuration and energy above its ground state? I don't see how this can be a valid statement. From what I see, we can say that Ea is highest for the halogens (Group 17), low for Group 1, lower for Group 2 and lowest for the noble gases (Group 18), and with lots of exceptions tends to rise in the p and d blocks. But looking at the data, it also is LOWEST at the end of a Block and in the block highest with the element that is 1 short of completing the shell. Wouldn't talking about the blocks be more accurate and useful? Ea isn't used all that much, but I think that might be partly because the way that it is taught is so flawed that is of little value. I propose the following, but I defer to others to decide whether it should be used and improved. "In examining the Periodic Table, it is clear that Eea is highest for the halogens (Group 17), low for Group 1, lower for Group 2 and lowest for the noble gases (Group 18). With lots of exceptions it tends to rise in the p and d blocks to the penultimate element then drops with the last element in the block (as is also seen in the s block). As would be expected, the addition of an electron to the halogens is especially exothermic since the shape of the p orbital being filled (citation needed) results in less shielding from the nucleus' positive charge. The same considerations lead to the prediction that the nobel gases, with the addition of an electron into a s orbital above the fully shielded nucleus of the neutral atom will have the lowest Eea's." 71.31.152.220 (talk) 10:44, 26 August 2012 (UTC)

"Electron affinity follows the trend of electronegativity."

This is clearly false. It's only true across the table, not down it. I changed the claim. 84.227.251.109 (talk) 07:50, 29 May 2014 (UTC)

It's not even true across the periodic table. Nitrogen is more electronegative than carbon, but the EA of an N atom is zero (or negative) yet the EA of carbon is positive (and substantial). And, by the way, although electronegativity increases monotonically from left to right across a period --in the s and p blocks,-- it does not in the d and f blocks. Furthermore, electronegativity does not uniformly decrease down a column in the p block of the period table. Germanium is more electronegative than silicon, lead is more electronegative than tin, and gallium and indium are both more electronegative than aluminum. Professor S. H. Strauss, Colorado State Univ. — Preceding unsigned comment added by 2601:282:8180:2336:888E:E521:538:9CC8 (talk) 14:49, 13 May 2016 (UTC)

Electron affinity (data page)

Stumbled upon Electron affinity (data page), which seems really weirdly named. Figured I'd ask somewhere with more watchers than that page if anyone had thoughts on whether the page should be renamed or merged into this one. Rusalkii (talk) 19:22, 27 August 2023 (UTC)

I think the data page is a separate article because it is so long. But it was only linked from the Elements (Atoms) section of this article; I have now added another link from the Molecules section of this article. Dirac66 (talk) 20:12, 27 August 2023 (UTC)