What group and period is Rubidium in?

Rubidium is in Group 1 (alkali metals) and Period 5 of the periodic table, directly below Potassium (K) and above Cesium (Cs).

Why is Rubidium so reactive?

Rubidium has a single valence electron in its outermost shell (5s1) that is loosely held because it is far from the nucleus. This makes it extremely easy to lose that electron, driving vigorous reactions with water, air, and halogens.

What are Rubidium's main uses?

Rubidium is used in atomic clocks (Rb-87 frequency standard), photoelectric cells, specialized glasses, and as a getter in vacuum tubes. Rb-82 is also used in positron emission tomography (PET) cardiac imaging.

Is Rubidium naturally radioactive?

Natural Rubidium consists of two isotopes: Rb-85 (72.17%, stable) and Rb-87 (27.83%, weakly radioactive with a half-life of ~49.23 billion years). Rb-87 decays to Sr-87 by beta emission and is used in Rb-Sr radiometric dating.

How does Rubidium compare to Potassium?

Rubidium sits directly below Potassium in Group 1. It is larger, heavier (85.47 vs 39.10 u), has a lower first ionization energy (403 vs 419 kJ/mol), and is more reactive. It has a similar electron configuration but with an extra electron shell.

Rubidium Element Properties

Look up every key property of Rubidium (Rb, Z=37) — from atomic mass and electron configuration to melting point and electronegativity.

Rb 37

Rubidium

Atomic number 37 · Group 1 · Period 5 · Alkali Metal

A soft, silvery-white metal that ignites spontaneously in air and reacts explosively with water.

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Identity & Classification

Atomic Structure

Physical Properties

Thermodynamic Properties

Chemical Properties

Notable Isotopes

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Summary

Rubidium (symbol Rb, atomic number 37) is a soft, silvery-white alkali metal in Group 1 of the periodic table. It is highly reactive, igniting spontaneously in air and reacting violently with water. This reference card consolidates its atomic, physical, chemical, electronic, and thermodynamic properties in a single, searchable view.

How it works

The page loads a complete, curated dataset of Rubidium properties.
Properties are grouped into thematic sections: identity, atomic structure, physical, thermodynamic, and chemical.
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Use cases

Quick reference during chemistry homework or exams.
Verify data for lab reports or research papers.
Compare Rubidium properties with neighboring alkali metals.
Study periodic trends (atomic radius, ionization energy, electronegativity).
Engineering calculations involving Rb-based atomic clocks or photovoltaics.
Teaching periodic table concepts with accurate, sourced data.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu