Question

How is hydrogen in heavy water different from hydrogen in normal water?

Answer 1

One or both atoms are a different isotope of Hydrogen, namely Deuterium (`""^2"H"` a.k.a. `"D"`) instead of Protium (`""^1"H"`).

Explanation:

One or both atoms of Hydrogen in heavy water are Deuterium - the stable isotope of Hydrogen that has a nucleus containing both a neutron and a proton instead of just a proton.

Deuterium (`""^2"H"` or `"D"`) has similar but not identical chemical properties to the much more common Protium (`""^1"H"`) isotope.