Uncharged atomic particle (7)
I believe the answer is:
neutron
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">uncharged atomic particle</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for neutron that I've seen before include "Subatomic particle with no electric charge" , "Chargeless particle" , "Uncharged atomic particle" , "one isn't charged" , "Uncharged subatomic particle" .)