Chemical element · Atomic number 37
Rubidium
Rubidium in the periodic table: atomic number 37, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Alkali metal
solid
85.468 u
Documented element sampleRubidium metal from a private element collection.
Image credit: Dnn87
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
Atomic classification
Shell occupancy
Rubidium in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 18 electrons
- N · n=4
- 8 electrons
- O · n=5
- 1 electron
- Electron configuration
- [Kr]5s1
- Electrons per shell
- 2 · 8 · 18 · 8 · 1
- Group
- 1
- Period
- 5
- Block
- S
- Element category
- Alkali metal
Physical and chemical properties
- Atomic mass
- 85.468 u
- Standard state
- solid
- Density
- 1.53 g/cm³
- Melting point
- 312.46 K
- Boiling point
- 961 K
- Electronegativity
- 0.82 (Pauling)
- First ionisation energy
- 4.177 eV
- Oxidation states
- +1
- Discovery
- 1861
Safety and periodic classification
Safety
Safe handling cannot be inferred from Rubidium's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Rubidium is in period 5, group 1 and the S block. Its direct neighbours by atomic number are Krypton and Strontium. The recorded Pauling electronegativity is 0.82. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.
Where Rubidium sits among the 118 elements
The table compares the reported values for Rubidium with every other element that carries the same value in the snapshot. A rank is not a judgement, it is orientation: it says how unusual this value is across the periodic table.
| Value | Rubidium | Position in the data set |
|---|---|---|
| Melting point | 312.46 K | Rank 87 of 103 elements with a reported value. Highest: Carbon. |
| Boiling point | 961 K | Rank 74 of 93 elements with a reported value. Highest: Rhenium. |
| Density | 1.53 g/cm³ | Rank 82 of 96 elements with a reported value. Highest: Osmium. |
| Electronegativity (Pauling) | 0.82 | Rank 93 of 95 elements with a reported value. Highest: Fluorine. |
| Ionisation energy | 4.177 eV | Rank 100 of 102 elements with a reported value. Highest: Helium. |
All values and ranks come from the PubChem Periodic Table snapshot, retrieved on 2026-07-15. Elements without a reported value are excluded, so the population differs per row.
The neighbours of Rubidium in the periodic table
- Place in the table
- Group 1, period 5, S block. Classified as alkali metal, solid at standard conditions.
- Direct neighbours
- Atomic number 37. Preceded by Krypton, followed by Strontium.
- Same group
- Same number of outer electrons, and therefore similar reactivity to Hydrogen, Lithium, Sodium, Potassium, Cesium, Francium.
- Discovery
- Recorded in the snapshot as: 1861. Who, where and under what circumstances is not part of that record, so this page carries the sourced year and no discovery narrative.
- Oxidation states
- +1. They follow from the electron configuration [Kr]5s1 and indicate which compounds to expect.
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