Radium (symbol Ra, atomic number 88) is a luminous radioactive metal once used in glow-in-the-dark paint. It is classified as a alkaline earth metal and sits in group 2, period 7 of the periodic table.
Overview
Radium is the chemical element with atomic number 88 and the symbol Ra. With a standard atomic weight of [226], it is a alkaline earth metal. In the periodic table it occupies group 2 and period 7, and under standard conditions it is normally a solid. Radium is a luminous radioactive metal once used in glow-in-the-dark paint.
Atomic structure
An atom of Radium has 88 protons in its nucleus and, when neutral, 88 electrons arranged in the configuration [Rn] 7s2. Radium has no stable isotope; the value [226] refers to the mass number of its most stable or most commonly produced isotope.
Discovery and place in the table
Radium was discovered in 1898 by Marie Curie, Pierre Curie. It follows Francium (Fr) and precedes Actinium (Ac) in order of atomic number.
| Atomic number | 88 |
|---|---|
| Symbol | Ra |
| Atomic mass | [226] |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 7 |
| Electron configuration | [Rn] 7s2 |
| Phase at STP | Solid |
| Discovered | 1898 (Marie Curie, Pierre Curie) |