Element 37 · Alkali metal
Rubidium (Rb) — Element 37
Latin rubidus — deep red
Rubidium (Rb) is an alkali metal in Period 5, Group 1 of the periodic table with atomic number 37, standard atomic weight 85.468 u, and ground-state electron configuration [Kr] 5s¹. At standard temperature and pressure it is classified as a solid with 1 valence electron and common oxidation states +1.
Atomic clocks, research
What are the atomic properties and physical constants of Rubidium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 37
- Standard atomic mass
- 85.468 u
- Chemical family
- Alkali metal
- Ground-state configuration
- [Kr] 5s¹
- Electrons per shell
- 2, 8, 18, 8, 1
- Valence electrons
- 1
- Common ion charges / oxidation states
- +1
- Phase at STP
- Solid
- Pauling electronegativity
- 0.82 Pauling
- First ionization energy
- 403 kJ/mol
- Atomic radius
- 265 pm
- Melting point
- 39 °C
- Boiling point
- 688 °C
- Discovery year
- 1861
- Table coordinate
- Period 5, Group 1
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Rubidium’s shells?
A neutral Rubidium atom contains 37 electrons distributed across 5 occupied principal energy shells ([Kr] 5s¹). The table below compares Rubidium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Rb | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 8 e⁻ | 32 e⁻ |
| n = 5 | O | 1 e⁻ | 50 e⁻ |
Frequently Asked Questions about Rubidium (Rb)
What is the atomic mass and atomic number of Rubidium (Rb)?
Rubidium (Rb) has atomic number Z = 37 (37 protons in its nucleus) and an IUPAC standard atomic weight of 85.468 u. It sits in Period 5, Group 1 and is classified as an alkali metal.
What is the ground-state electron configuration of Rubidium?
The neutral ground-state electron configuration of Rubidium (Z = 37) is [Kr] 5s¹. Across its 5 occupied principal shells (n = 1 to n = 5), the electrons per shell are 2, 8, 18, 8, 1, with 1 valence electron participating in bonding.
What are the common ion charges and electronegativity of Rubidium?
Rubidium commonly forms +1 oxidation states or ion charges in compounds. Its Pauling electronegativity is 0.82 and its first ionization energy is 403 kJ/mol.
When was Rubidium discovered and what is it used for?
Rubidium was discovered in 1861 (Latin rubidus — deep red). Atomic clocks, research
How does Rubidium compare to neighboring elements?
Other alkali metal elements: