---
title: "Rubidium (Rb): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/rubidium.html
description: "Rubidium (Rb), element 37: atomic mass 85.468, electron configuration [Kr] 5s¹, group 1, period 5, s-block alkali metal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
37Rb85.468

# Rubidium (Rb) – element 37

Rubidium is a chemical element with the symbol **Rb** and atomic number **37**. It is a alkali metal in group 1 (alkali metals), period 5 of the periodic table (s-block), and is a solid at room temperature.

Rubidium (Rb) has atomic number 37, atomic mass 85.468 u and electron configuration [Kr] 5s1.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Rubidium facts

| Symbol | Rb |
| --- | --- |
| Atomic number | 37 |
| Atomic mass | 85.468 u (g/mol) |
| Category | alkali metal |
| Group | group 1 (alkali metals) |
| Period | 5 |
| Block | s-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 |
| Noble-gas notation | [Kr] 5s1 |
| Electrons per shell | 2, 8, 18, 8, 1 |
| Valence electrons | 1 |

## Bohr model and shells

Rubidium has 37 electrons in 5 shells: 2, 8, 18, 8, 1. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 312.45 K (39.3 °C) |
| --- | --- |
| Boiling point | 961 K (687.9 °C) |
| Density | 1.532 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Electron affinity | 46.884 kJ/mol |
| Ionization energies | 403, 2633, 3860 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 31.06 J/(mol·K) |
| Discovered by | Robert Bunsen |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Rb.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of rubidium?

The atomic mass of rubidium is 85.468 u, so one mole of rubidium atoms weighs 85.468 g.

### What is the electron configuration of rubidium?

Rubidium has 37 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹, or [Kr] 5s¹ in noble-gas notation. Electrons per shell: 2, 8, 18, 8, 1.

### How many valence electrons does rubidium have?

Rubidium has 1 valence electron (group 1).

### Is rubidium a metal?

Yes. Rubidium is a alkali metal.

### Where is rubidium on the periodic table?

Rubidium is in group 1 (alkali metals), period 5, in the s-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.