Radium (Ra)
Alkaline earth metal · s-block · period 7 · group 2
Silvery-white metal that glows with a faint blue light and blackens in air.
Radium (symbol Ra) is chemical element number 88, a alkaline earth metal in group 2, period 7 of the periodic table. Its standard atomic weight is (226) and its electron configuration is [Rn] 7s2. At room temperature it is a solid, and it is radioactive. A million times more radioactive than the same mass of uranium.
Properties
| Atomic number | 88 |
|---|---|
| Atomic mass | (226) |
| Category | Alkaline earth metal |
| Block | s-block |
| Group · Period | 2 · 7 |
| Electron configuration | [Rn] 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 2 |
| State at 25 °C | solid |
| Melting point | 973 K |
| Boiling point | 2010 K |
| Density | 5.5 g/cm³ |
| Electronegativity (Pauling) | 0.9 |
| Radioactive | Yes — no stable isotope |
| Origin | decay |
| Discovered | 1898 · Marie & Pierre Curie |
Key facts about Radium
- A million times more radioactive than the same mass of uranium.
- Its eerie glow made it a craze — radium watch dials, toothpaste and tonics — before the dangers were understood.
- The 'Radium Girls', who painted watch dials, suffered terrible radiation injuries and won a landmark safety lawsuit.
- Marie Curie's notebooks are still too radioactive to handle safely.
What Radium is used for
Historically luminous paint and cancer therapy; now almost entirely replaced by safer isotopes.
Where it sits in the periodic table
Radium is in group 2, period 7, of the s-block. Its electron configuration [Rn] 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Radium on the interactive table →
Radium — frequently asked questions
What is Radium used for?
Historically luminous paint and cancer therapy; now almost entirely replaced by safer isotopes.
Is Radium radioactive?
Yes. Radium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Radium?
Radium has the electron configuration [Rn] 7s2, which is 2, 8, 18, 32, 18, 8, 2 electrons per shell.
What group and period is Radium in?
Radium is in group 2, period 7, in the s-block. Its outer shell holds 2 electrons.
Who discovered Radium?
Radium was discovered in 1898 by Marie & Pierre Curie.