Question

Why is the election affinity of beryllium negative?

Answer 1

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

https://files.mtstatic.com/

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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(ul(color(white)(uarr darr))" "ul(color(white)(uarr darr))" "ul(color(white)(uarr darr)))`
`" "" "" "color(white)(.)2p`
`" "`
`" "`
`" "`
`" "`
`ul(uarr darr)`
`color(white)(.)2s`

`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`
`" "`

`ul(uarr darr)`
`color(white)(.)1s`

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