In our electron pump, when you turn the crank, one side gets a surplus of electrons, or a negative charge, and on the other side the atoms are missing said electrons, resulting in a positive charge.
Said here means which are mentioned earlier in the text , or, simply, these .
The sentence could be rephrased thus: In our electron pump, when you turn the crank, one side gets a surplus of electrons, or a negative charge, and on the other side the atoms are missing these electrons, resulting in a positive charge.
So, as an atom misses an electron (the electron's orbital is empty), it assumes positive charge.
ell.stackexchange.com/users/2127/CowperKettle
I had problems with that particular word as well until I learned to add in my head " ...
the XXX that we have said something about previously... ".
" the atoms are missing said electrons " becomes "the atoms are missing the electrons that we have said something about previously "
ell.stackexchange.com/users/4926/Konrad Viltersten
I think you have misunderstood the big picture.
BOTH sides of the pump have atoms both before and after.
Before the "crank is turned", every atom has exactly the right number of electrons.
Afterwards, one side has extra electrons and the other side has fewer electrons.
ell.stackexchange.com/users/4484/leoger
To add to CopperKettle's answer, said is normally only used this way in legal documents.
(For instance in a police report or a contract.)
Sometimes people use it in normal, non-legal writing too.
I guess they do that for humorous effect.
There's no need to use it that way yourself.
ell.stackexchange.com/users/6472/Dangph
Adjectives are used to describe a noun or pronoun.
"
Said" is used as an adjective in a legal or formal context to avoid any potential for misinterpretation of the sentence which may arise from misidentifying a previously described subject noun.
If there is no potential for confusion of the subject noun then the adjective "said" is redundant
and it's primary use
is as an affectation intended to make the speaker sound more intelligent, which rarely works.
In the example given, there is no need to clarify which electrons are missing so the adjective (said) failed to either clarify the sentence or add to the authors perceived intellect.
ell.stackexchange.com/users/19049/Johny Ellis
In our electron pump, when you turn the crank, one side gets a surplus of electrons, or a negative charge, and on the other side  the atoms are missing said electrons , resulting in a positive charge.   The part in a bold font is confusing to me. I can't make grammatical sense of it. One side gets a surplus of electrons and the other side gets the atoms. How does  are missing said electrons  fit into the rest of the sentence?
"said" as an adjective
ell.stackexchange.com
<word-meaning>
ell.stackexchange.com/questions/30739
ell.stackexchange.com/users/6450/Michael Rybkin
"Said" is used as an adjective in a legal or formal context to avoid any potential for misinterpretation of the sentence which may arise from misidentifying a previously described subject noun. Said is an adjective used in legal contexts.
Said is an adjective used in legal contexts.