rubidium

American  

[roo-bid-ee-uhm] / ruˈbɪd i əm /

noun

Chemistry.

1. a silver-white, metallic, active element resembling potassium, used in photoelectric cells and radio vacuum tubes. Rb; 85.47; 37; 1.53 at 20°C.

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rubidium British  

/ ruːˈbɪdɪəm /

noun

1. a soft highly reactive radioactive element of the alkali metal group; the 16th most abundant element in the earth's crust (310 parts per million), occurring principally in pollucite, carnallite, and lepidolite. It is used in electronic valves, photocells, and special glass. Symbol: Rb; atomic no: 37; atomic wt: 85.4678; half-life of ⁸⁷ Rb: 5 × 10 ¹¹ years; valency: 1, 2, 3, or 4; relative density: 1.532 (solid), 1.475 (liquid); melting pt: 39.48°C; boiling pt: 688°C

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rubidium Scientific  

/ ro̅o̅-bĭd′ē-əm /

1. A soft, silvery-white metallic element of the alkali group. It ignites spontaneously in air and reacts violently with water. Rubidium is used in photoelectric cells, in making vacuum tubes, and in radiometric dating. Atomic number 37; atomic weight 85.47; melting point 38.89°C; boiling point 688°C; specific gravity (solid) 1.532; valence 1, 2, 3, 4.

2. See Periodic Table

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Other Word Forms

• rubidic
  adjective

Etymology

Origin of rubidium

1860–65; < New Latin, equivalent to Latin rūbid ( us ) red (in allusion to the two red lines in its spectrum) + -ium -ium

Example Sentences

The team confined thousands of rubidium atoms so they could only move along a single straight line, using a combination of magnetic and optical fields.

From Science Daily • Jan. 7, 2026

Magnetic readings depend on a sensor head about the size of a finger that uses lasers and rubidium atoms.

From The Wall Street Journal • Nov. 20, 2025

Because a vanadium peroxide molecule is negatively charged, it needed alkali cations for charge balance, Nyman said, and the researchers used potassium, rubidium and cesium alkali cations for this study.

From Science Daily • Feb. 12, 2024

First, they cooled a cloud of rubidium atoms to just shy of absolute zero.

From Scientific American • Oct. 4, 2023

The separation of lithium, cæsium, and rubidium is seldom called for, owing to their rarity.

From A Text-book of Assaying: For the Use of Those Connected with Mines. by Beringer, Cornelius