# Why is the election affinity of beryllium negative?

Aug 12, 2017

Well, beryllium has a POSITIVE electron affinity, because it gets less stable when we try to fill the next orbitals, the $2 p$ orbitals... but I suppose even atoms can dislike certain electoral processes...

The electron affinity is the change in energy due to adding a new electron to an atom or molecule. The to-scale electronic structure of beryllium is:

$\underbrace{\underline{\textcolor{w h i t e}{\uparrow \downarrow}} \text{ "ul(color(white)(uarr darr))" } \underline{\textcolor{w h i t e}{\uparrow \downarrow}}}$
$\text{ "" "" } \textcolor{w h i t e}{.} 2 p$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\underline{\uparrow \downarrow}$
$\textcolor{w h i t e}{.} 2 s$

$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$
$\text{ }$

$\underline{\uparrow \downarrow}$
$\textcolor{w h i t e}{.} 1 s$

And so, it takes energy input in order to place a new electron into a $2 p$ orbital. Thus, "EA"("Be") > 0.