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Rubidium

Element 37 · Alkali metal

Specimen

Atomic number
37
Atomic mass
85.468
State at room temperature
Solid
Melting point
39.31 °C
Boiling point
687.9 °C
Density
1.53 g/cm³
Discovered
1861

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Not needed, little harm known. Food contains traces of rubidium, and the body takes it up because it is similar to potassium. An average person holds about half a gram. The RSC calls rubidium non-toxic. There are few studies of it. 3

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The atom

Rb
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 8
5 (O) outermost 1
Total37

Configuration [Kr] 5s¹

5s ↑
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 37 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Kr core, with one arrow per electron.

Related elements

Group 1
H Hydrogen Li Lithium Na Sodium K Potassium Cs Caesium Fr Francium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    Royal Society of Chemistry, 2026. Rubidium - Element information, properties and uses .

    • Rubidium has no known biological role and is non-toxic. However, because of its chemical similarity to potassium we absorb it from our food, and the average person has stores of about half a gram.
  4. 4

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.