Extension of the periodic table beyond the seventh period Reference Libraries
Actinium is a radioactive chemical element. The symbol for Actinium is Ac and the atomic number is 89. Actinium was discovered in 1899 by French chemist AndrÃ©-Louis Debierne. It was the first non-primordial radioactive element to be isolated. Actinium is amongst a group of 15 similar elements within the periodic table that make up the actinoid series. This substance was also independently...
- A person who stands up for something, as contrasted to a bystander who remains inactive.
- One of the upright handlebars on a traditional Inuit sled.