Could someone confirm this?

[enTropeeeeeeeee]

Electron affinity is the measure of how much energy is released when a certain atom gains an electron. This will be a negative value because it is an exothermic process. Whatever this value is, the absolute value will determine how much energy is required to remove the electron from said atom (AKA the ionization energy).

Thanks!

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[tttgo]

The first sentence is right, but I don't think you get the ionization energy by simply taking the absolute value. I think electron affinity can sometimes be endothermic.

 

[ilovemcat]

Electron affinity is the measure of how much energy is released when a certain atom gains an electron. This will be a negative value because it is an exothermic process. Whatever this value is, the absolute value will determine how much energy is required to remove the electron from said atom (AKA the ionization energy).

Thanks!

Electron Affinity is a measure of energy change for the gain of one electron. You're right that energy is released when some atoms gain an electron (exothermic process), but this isn't always the case. If you look at any 6th group element like Nitrogen (half-filled p subshell) or any 2nd group element like Beryllium (filled s subshell) - they are somewhat stable. For elements in these two groups, adding an electron would require an input of energy (endothermic process). Nobel Gases are also require a large input of energy since they are extremely stable. Aside from these exceptions, the general trend is that more energy is released from left to right across a period.

Now for a particular element, the value of Electron Affinity does NOT equal the value of Ionization Energy. Although they follow similar trends, these two values are entirely different.

 

[Rabolisk]

Every element's ionization energy is endothermic, but electron affinity may be either exothermic or endothermic. For elements that form stable anions, the electron affinity is almost always exothermic, although the second electron affinity (analogous to second ionization energy) is generally endothermic for most elements, if not all elements. Generally, an endothermic electron affinity is hard to measure, which is why some tables will just list <0 (or >0) for those elements. Nitrogen is known to have an electron affinity that is barely endothermic.

 

[enTropeeeeeeeee]

Electron Affinity is a measure of energy change for the gain of one electron. You're right that energy is released when some atoms gain an electron (exothermic process), but this isn't always the case. If you look at any 6th group element like Nitrogen (half-filled p subshell) or any 2nd group element like Beryllium (filled s subshell) - they are somewhat stable. For elements in these two groups, adding an electron would require an input of energy (endothermic process). Nobel Gases are also require a large input of energy since they are extremely stable. Aside from these exceptions, the general trend is that more energy is released from left to right across a period.

Now for a particular element, the value of Electron Affinity does NOT equal the value of Ionization Energy. Although they follow similar trends, these two values are entirely different.

Every element's ionization energy is endothermic, but electron affinity may be either exothermic or endothermic. For elements that form stable anions, the electron affinity is almost always exothermic, although the second electron affinity (analogous to second ionization energy) is generally endothermic for most elements, if not all elements. Generally, an endothermic electron affinity is hard to measure, which is why some tables will just list <0 (or >0) for those elements. Nitrogen is known to have an electron affinity that is barely endothermic.

This made complete sense. Thanks to the both of ya!

 

[enTropeeeeeeeee]

Every element's ionization energy is endothermic, but electron affinity may be either exothermic or endothermic. For elements that form stable anions, the electron affinity is almost always exothermic, although the second electron affinity (analogous to second ionization energy) is generally endothermic for most elements, if not all elements. Generally, an endothermic electron affinity is hard to measure, which is why some tables will just list <0 (or >0) for those elements. Nitrogen is known to have an electron affinity that is barely endothermic.

Would Na ionization energy still be endothermic? I would imagine that it really wants to lose its electron and become Ne.

 

[ilovemcat]

Would Na ionization energy still be endothermic? I would imagine that it really wants to lose its electron and become Ne.

I agree with you but I looked it up on google and according to various sources, Sodium releases 52.8 kJ of energy per mol (exothermic process). For what reason, I can't really explain

All negative values just mean that much energy needs to be added for it to accept the electron. All positive values mean energy is released. That's the convention they use.

 

[enTropeeeeeeeee]

I agree with you but I looked it up on google and according to various sources, Sodium releases 52.8 kJ of energy per mol (exothermic process). For what reason, I can't really explain

All negative values just mean that much energy needs to be added for it to accept the electron. All positive values mean energy is released. That's the convention they use.

The MCAT is great because I'm learning SOOO MUCH every single day. The MCAT is terrible because I'm realizing how little I know! Socrates said something like that too .

 

[ilovemcat]

The MCAT is great because I'm learning SOOO MUCH every single day. The MCAT is terrible because I'm realizing how little I know! Socrates said something like that too .

Great attitude, haha.

 

[Rabolisk]

I think entropee asked for Na's ionization energy, not electron affinity. But it does turn out that all ionization energies are endothermic, even for alkali metals. This results in an interesting and unintuitive phenomenon; it is more favorable for sodium to gain an electron and become Na- than it is for it to lose an electron and become Na+. Based on this, alkalides have been synthesized.

http://en.wikipedia.org/wiki/Alkalide
http://www.google.com/imgres?imgurl...Wtweip5ToAw&page=1&ndsp=18&ved=1t:429,r:7,s:0

 

[enTropeeeeeeeee]

I think entropee asked for Na's ionization energy, not electron affinity. But it does turn out that all ionization energies are endothermic, even for alkali metals. This results in an interesting and unintuitive phenomenon; it is more favorable for sodium to gain an electron and become Na- than it is for it to lose an electron and become Na+. Based on this, alkalides have been synthesized.

http://en.wikipedia.org/wiki/Alkalide

So after doing some more digging....

Although Na (neutral) ----> Na+ is pretty easy to accomplish because the cationic form gives a filled shell and consequently stability. However, it still takes some heat energy to eject the lone electron from the electron cloud. Therefore this, and all ionization energies are endothermic.

 

[ridethecliche]

The MCAT is great because I'm learning SOOO MUCH every single day. The MCAT is terrible because I'm realizing how little I know! Socrates said something like that too .

You made a funny!!!

To be honest, I'm not against the idea of learning while taking a test. Some of the exams I did best in while in undergrad (orgo comes to mind) were ones where I was figuring stuff out and making things work as I went along.

Realize that the books you're using go ABOVE AND BEYOND what you need to know, so if you're not getting something minutia you shouldn't let that get you down. At some point, staring at the same page for hours isn't going to help you so you should look up other resources on the matter. Wikipremed's site has a bunch of links to other notes and wikipedia. I found myself reading about conservation of energy on there tonight, because while I understand the concept, EK does a terrible job of giving good examples.

I'm guessing that BR is good for doing a problem 'with' you while you're working through stuff, because EK falls short on the application of what you're learning especially in physics. There's a book a teacher in highschool gave me called 'conceptual physics'. There is no 'math' in the entire book. It's all just conceptual understanding and solving in terms of other things. I might try looking for it when I go home because it's a nifty little book.

And now I've taken this thread COMPLETELY off topic...