How does a negative ion differ from an uncharged atom of the same element?

When an atom or molecule accepts or looses an electron or electrons it gets either negative charge (when electrons gained) or a positive charge (when looses electron). The negative ion is called Anion and positve ion is called the Cation. An Ion can be Atomic or Polyatomic.

Example:
              Sodium when looses one electron forms a cation i.e. Na⁺

              Chlorine when gains one electron forms an Anion i.e. Cl⁻

Result:
          A negative ion (Anion) differ from an uncharged atom of the same element in the number of electrons. An anion contains more electrons than its corresponding Neutral Element.

If the water vapor content stays the same and the temperature drops, then the relative humidity increases. its vise versa.if the water vapor content stats the same and the temperature rises, the relative humidity decreases. so, yes, i'd say that temperature and humidity have a strong relationship.