Electron affinity negative & positive confusion

[deleted738762]

I was reading over my notes and I know electron affinity is negative for elements that want to gain an electron like Cl-. You only have a positive electron affinity if you don't want the electrons like Neon, which makes it endothermic.

However, according to wikipedia it states "The atom of another element (usually nonmetal), whose electron affinity is positive, then accepts the electron(s), again to attain a stable electron configuration, and after accepting electron(s) the atom becomes an anion."

Shouldn't its electron affinity be negative? Because the non-metal wants to gain an electron to be stable. This what I understood from chad's lecture.

Thanks

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[osker246]

Take a step back and think what affinity means. It's an attraction right? So when it comes to electrons and charges, does a electron prefer a positive or negative? Having a positive affinity means the atom has a increased attraction to an electron. The reason electron affinity increases across a period is due to the increase in stability of the electron configuration (lower energy state). Negative affinity means an atom does not want to gain an electron because it's electron configuration is already stable. Cl- has a negative electron affinity because it has reached a stable configuration ( octet rule).

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[deleted738762]

I learned it as if an element has a higher electron affinity it would be negative, not positive. According to chads unless I am mistaken

 

[osker246]

What do you mean by an element being negative? Like elemental chlorine becoming an anion?

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[deleted738762]

What do you mean by an element being negative? Like elemental chlorine becoming an anion?

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No it's electron affinity value is negative. For example, chloride loves to gain an electron because it becomes stable and is a highly exothermic process, hence the electron affinity value is negative. Elements that don't want to gain electrons like noble gases have a positive value, because they are endothermic processes.

This what I learned in Chad, anyone care to chime in?

 

[osker246]

My mistake! I totally misunderstood what you were asking and it's been awhile since I've even thought about chemistry. I have actually have been thinking about your original question, I can not find the original quote on wikipedia to read for context. Skimming through wikipedia I believe the confusion lies with the sign convention they list. According to wikipedia, E.A = -Delta(E), Where E.A = electron affinity and Delta(E)=Total energy. The more positive the E.A, the more spontaneous and more negative Delta(E) is based on E.A = -Delta(E). So when you say more negative electron affinity, wikipedia refers to this as more negative total energy. Which pretty much means its an exothermic process to a more stable configuration.