88226RaRadium
Radium (Ra) — element 88alkaline earth metal · group 2, period 7
Radium is a chemical element with the symbol Ra and atomic number 88. It is an alkaline earth metal in group 2, period 7 of the periodic table (the s-block), with a standard atomic mass of 226 u. At room temperature (25 °C) radium is a solid.
💡 Known for: Discovered by the Curies; once used in glow-in-the-dark watch dials before its dangers were understood.
# Radium properties
| Symbol | Ra |
|---|---|
| Atomic number | 88 |
| Atomic mass | 226 u |
| Category | alkaline earth metal |
| Group | 2 |
| Period | 7 |
| Block | s-block |
| Electron configuration | [Rn] 7s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s² |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 2 |
| Protons / electrons | 88 / 88 |
| State at 25 °C | solid |
| Melting point | 973 K (699.9 °C, 1291.7 °F) |
| Boiling point | 2010 K (1736.8 °C, 3158.3 °F) |
| Density | 5.5 g/cm³ |
| Electronegativity (Pauling) | 0.9 |
| First ionization energy | 5.279 eV |
| Atomic radius | 283 pm |
| Discovered | 1898 |
# Electron configuration of radium
The electron configuration of radium is [Rn] 7s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s². Its 88 electrons fill 7 shells as 2, 8, 18, 32, 18, 8, 2, so the outermost shell holds 2 electrons. As a group 2 element, radium has 2 valence electrons.
# Related elements
FrFranciumprevious elementAcActiniumnext elementBeBerylliumgroup 2MgMagnesiumgroup 2CaCalciumgroup 2SrStrontiumgroup 2BaBariumgroup 2
# Radium FAQ
What is the atomic number of radium?
The atomic number of radium is 88: every radium atom has 88 protons in its nucleus. Its symbol is Ra.
What is the atomic mass of radium?
The standard atomic mass of radium is 226 u.
What is the electron configuration of radium?
Radium's electron configuration is [Rn] 7s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s²), with 2, 8, 18, 32, 18, 8, 2 electrons per shell.
Is radium a metal?
Yes. Radium is an alkaline earth metal, one of the metals.
What is the melting point of radium?
Radium melts at 973 K (699.9 °C, 1291.7 °F) and boils at 2010 K (1736.8 °C, 3158.3 °F).
What is radium used for / known for?
Discovered by the Curies; once used in glow-in-the-dark watch dials before its dangers were understood.