How do you call the opposite of an ion?

According to IUPAC, an ion is defined as:



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> An atomic or molecular particle having a net electric charge. ([source](https://doi.org/10.1351/goldbook.I03158))
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But how do you call an atomic or molecular particle that does not have a net electric charge? Is there a noun or an adjective that one can use to refer to the opposite of an ion?


