Radium (Ra) is a chemical element with atomic number 88. It is the heaviest of the so called alkaline earth metals, which is the group it belongs to.
Like its name suggests, radium is a highly radioactive element. In the early 1900s, radium was sometimes added to products such as toothpastes, and even food products, because of its supposed health benefits. Thankfully this is no longer the case, as radium is very dangerous and can cause radiation poisining and cancer.