After a chemical change, the substance always changes. It's only after a physical change that the substance does not change. Hope I helped :)
Not 100% if this answers however:
The radium nucleus turns into radon-222 nucleus, itself radioactive, containing two protons and two neutrons less. The disintegration releases 4.6 million electronvolts of energy. The alpha particle carries the 222/226ths of this available energy and the radon 4/226ths.
We will need to see what the picture looks like post the picture of the molecule
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