Praseodymium, Chemical Element

During the late 1830s and early 1840s, Swedish chemist Carl Gustav Mosander (1797-1858) was studying two puzzling minerals, ceria and yttria. Both minerals had been discovered more than fifty years earlier in remote parts of Sweden.

Promethium, Chemical Element

Promethium is one of the most fascinating of all chemical elements. It has never been found on the Earth's surface.

Protactinium, Chemical Element

Protactinium is one of the rarest elements on Earth. It is formed when uranium and other radioactive elements break down.

Radium, Chemical Element

Radium is luminescent, meaning it gives off radiation that can be seen in the dark. Because of its radiation, however, it has relatively few uses.

Radon, Chemical Element

Radon is the last member of the noble gas family. The noble gases are the elements that make up Group 18 (VIIIA) of the periodic table.

Rhenium, Chemical Element

Rhenium was discovered by a German research team that included Walter Noddack (1893-1960), Ida Tacke (1896-1979) and Otto Berg. These scientists knew that there were two empty boxes in the periodic table that represented elements that had not yet been discovered.

Rhodium, Chemical Element

Rhodium is considered to be a precious metal. A precious metal is one that is rare and valued.

Rubidium, Chemical Element

Rubidium is a soft, silvery metal. It is one of the most active chemical elements.

Ruthenium, Chemical Element

Ruthenium belongs in the platinum group of metals. The elements in this group are named after the best known member of the group, platinum.

Samarium, Chemical Element

Samarium is one of the rare earth elements found in Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other.

Scandium, Chemical Element

The existence of scandium was predicted nearly ten years before it was actually discovered. The prediction was made by Russian chemist Dmitri Mendeleev (1834-1907).

Selenium, Chemical Element

Selenium is a member of the chalcogen family. The chalcogens are elements in Group 16 (VIA) of the periodic table.

Silicon, Chemical Element

Silicon is a member of Group 14 (IVA) in the periodic table. The periodic table is a chart that shows how chemical elements are related to one another.

Silver, Chemical Element

Chemists classify silver as a transition metal. The transition metals are elements between Groups 2 and 13 in the periodic table.

Sodium, Chemical Element

Most people have never seen sodium metal. But it is almost impossible not to see many compounds of sodium every day.

Strontium, Chemical Element

Strontium is a member of the alkaline earth metals. The alkaline earth metals make up Group 2 (IIA) of the periodic table.

Sulfur, Chemical Element

Sulfur belongs to the chalcogen family. Other members of the family are oxygen, selenium, tellurium, and polonium.

Tantalum, Chemical Element

Tantalum is a transition metal in Group 5 (VB) of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another.

Technetium, Chemical Element

Technetium is the only element below uranium that does not exist on Earth. It is a synthetic (man-made) element produced in a particle accelerator.

Tellurium, Chemical Element

The elements that make up Group 16 (VIA) of the periodic table are sometimes called the chalcogens. This name comes from the Greek word for "bronze ore," chalkos.

Terbium, Chemical Element

Terbium is classified as a rare earth element. The term is misleading because terbium is more common than metals such as silver and mercury.

Thallium, Chemical Element

Thallium was first discovered by means of a spectroscope. A spectroscope is a device for analyzing the light produced when an element is heated.