Radium (Ra): electron configuration, atomic mass and facts
Radium (Ra) is element 88 of the periodic table, an alkaline earth metal in period 7, group 2. Its electron configuration is [Rn] 7s2, with electrons arranged in shells 2, 8, 18, 32, 18, 8, 2, and its most stable isotope has mass number 226.
💡 Discovered by the Curies in 1898. It glows faintly in the dark.
▶ Watch Radium’s electrons orbit in the interactive periodic tableRadium at a glance
| Symbol | Ra |
|---|---|
| Atomic number | 88 |
| Atomic mass | [226] u (most stable isotope) |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 7 |
| Block | s-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s2 |
| Noble-gas shorthand | [Rn] 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 2 |
| Outer-shell electrons | 2 |
| Electronegativity (Pauling) | 0.9 |
| State at 20 °C | solid |
Where is Radium on the periodic table?
Radium is in period 7, group 2, in the s-block. The period number matches its 7 electron shells, and the block names the subshell its last electrons fill. In the same group, Barium sits directly above it. Elements in one group have the same number of outer-shell electrons (2 here), which is why they react in similar ways.
How to work out the electron configuration of Radium
Put 88 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁶ (36), 5s² (38), 4d¹⁰ (48), 5p⁶ (54), 6s² (56), 4f¹⁴ (70), 5d¹⁰ (80), 6p⁶ (86), 7s² (88). In shorthand, [Rn] stands for the 86 electrons of radon, giving [Rn] 7s².
How electronegative is Radium?
Radium has a Pauling electronegativity of 0.9, ranking 95 of the 100 elements with a known value (fluorine is highest at 3.98). That is low: it tends to give up electrons and form positive ions.
Frequently asked questions
What is the electron configuration of Radium?
The electron configuration of Radium (Ra) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s2. In noble-gas shorthand it is written [Rn] 7s2.
How many electrons does Radium have in each shell?
Radium has 88 electrons arranged in shells as 2, 8, 18, 32, 18, 8, 2. It has 2 electrons in its outer shell.
What is the atomic mass of Radium?
Radium has no stable isotopes. Its most stable isotope has a mass number of 226.
Is Radium a metal?
Yes. Radium is an alkaline earth metal.
Explore nearby elements
More alkaline earth metals: Beryllium, Magnesium, Calcium, Strontium, Barium. See all elements on the periodic table.