Barium (Ba): electron configuration, atomic mass and facts
Barium (Ba) is element 56 of the periodic table, an alkaline earth metal in period 6, group 2. Its electron configuration is [Xe] 6s2, with electrons arranged in shells 2, 8, 18, 18, 8, 2, and its standard atomic weight is 137.33 u.
💡 Burns apple-green. Barium sulfate “meals” show the gut on X-rays.
▶ Watch Barium’s electrons orbit in the interactive periodic tableBarium at a glance
| Symbol | Ba |
|---|---|
| Atomic number | 56 |
| Atomic mass | 137.33 u |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 6 |
| Block | s-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2 |
| Noble-gas shorthand | [Xe] 6s2 |
| Electrons per shell | 2, 8, 18, 18, 8, 2 |
| Outer-shell electrons | 2 |
| Electronegativity (Pauling) | 0.89 |
| State at 20 °C | solid |
| Flame test colour | apple green |
Where is Barium on the periodic table?
Barium is in period 6, group 2, in the s-block. The period number matches its 6 electron shells, and the block names the subshell its last electrons fill. In the same group, Strontium sits directly above it and Radium sits directly below 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 Barium
Put 56 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). In shorthand, [Xe] stands for the 54 electrons of xenon, giving [Xe] 6s².
How electronegative is Barium?
Barium has a Pauling electronegativity of 0.89, ranking 96 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.
Barium in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain barium: Barium hydroxide, Barium chloride. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Barium?
The electron configuration of Barium (Ba) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2. In noble-gas shorthand it is written [Xe] 6s2.
How many electrons does Barium have in each shell?
Barium has 56 electrons arranged in shells as 2, 8, 18, 18, 8, 2. It has 2 electrons in its outer shell.
What is the atomic mass of Barium?
The standard atomic weight of Barium is 137.33 u, so one mole of Barium atoms has a mass of about 137.33 g.
Is Barium a metal?
Yes. Barium is an alkaline earth metal.
Explore nearby elements
More alkaline earth metals: Beryllium, Magnesium, Calcium, Strontium, Radium. See all elements on the periodic table.