Radium is the chemical element with atomic number 88 and symbol . It is a alkaline earth metal. All its isotopes are radioactive. Its chemistry resembles that of barium, often favoring the state, while radioactive decay distinguishes its long-term behavior from an ordinary stable alkaline-earth salt.[ref]
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Discovered by Marie Curie when she noticed that there was some yet unknown more radioactive element in their raw samples, after uranium and polonium, which she published 6 months prior, had already been separated. Published on December 1989 as: Section "Sur une nouvelle substance fortement radio-active, contenue dans la pechblende".
The uranium 238 decay chain is the main source of naturally occurring radium.