week 7:   RADON!   one of the 6 "Noble Gasses" , which used to be called rare gasses, but Argon is not so rare, and "inert gas" is a misnomer too since several do take part in chemical reactions.

Rn : atomic # 86, #neutrons=136, has 6 energy levels. Colorless, odorless gas with a cubic crystal structure. Discovered in 1898 by Freidrich Ernst Dorn. It's a radioactive gas that emanates from radium compounds, i.e. is obtained from a radium chloride source (the kind used in cancer treatment anyway). Radium and radon are not used in x-ray medical radiography like they used to be.... it is also produced during the operation of nuclear power plants. It is probably what killed Marie Curie in the end.....

Radon is a contaminant of indoor air that causes 21,000 LUNG cancer deaths in the US per year, the second leading cause of lung cancer after cigarettes. It can accumulate in buildings from natural sources beneath them-- soil and rock!    AAAAACK!