Rubidium (Rb)

Rubidium properties

Atomic number

37

Atomic mass

85.468 u

Category

Alkali metal

Group

1

Period

5

Block

s-block

State at room temp.

Solid

Electronegativity

0.82

Melting point

312.45 K (39.3 °C)

Boiling point

961 K (687.8 °C)

Density

1.532 g/cm³

Valence electrons

1

Common charges

+1

Oxidation states

+1

Atomic radius

303 pm

Ionization energy

4.177 eV

Electron affinity

0.468 eV

Radioactive

No, has stable isotopes

Discovered

1861

Rubidium electron configuration

The electron configuration of Rubidium (Rb) is [Kr] 5s1. Its 37 electrons are arranged in shells as 2, 8, 18, 8, 1.

Protons, neutrons and electrons in Rubidium

A neutral Rubidium atom has 37 protons and 37 electrons. Most Rubidium atoms have about 48 neutrons: the atomic mass rounded to 85, minus the atomic number 37.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Rubidium have?

1

Rubidium has 1 valence electron in its outermost shell, shell 5. These are the electrons involved in chemical bonding.

See every element: Periodic table with valence electrons

Rubidium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Rubidium

85.468 g/mol

One mole of Rubidium atoms (6.022 × 10²³ atoms) has a mass of 85.468 grams. Use this value to convert between grams and moles.

Rubidium facts

• Rubidium melts at about 39 °C, so a sample could turn liquid on a very hot day.
• In 1995 physicists cooled rubidium atoms to less than a millionth of a degree above absolute zero, creating the first Bose-Einstein condensate.
• Rubidium (Rb) has atomic number 37 and is a solid at room temperature. It was discovered in 1861.

Position in the periodic table

Rubidium is element 37, in period 5 and group 1 of the periodic table, in the s-block.

All alkali metals

Uses of Rubidium

Rubidium is used in compact atomic clocks, found in GPS satellites and in the base stations of mobile phone networks. Rubidium-82, a short-lived radioactive isotope, is used in PET scans that show blood flow to the heart. Physicists use rubidium vapor in laser-cooling experiments and sensitive magnetometers, but because it is costly and highly reactive, rubidium has few large-scale uses.

Who discovered Rubidium?

German scientists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 in Heidelberg, using their newly invented spectroscope to examine the mineral lepidolite. They named it after the Latin rubidus, meaning 'deep red', for the color of its brightest spectral lines.

Where does the name come from?

Rubidium comes from the Latin rubidus, meaning 'deep red'. Robert Bunsen and Gustav Kirchhoff discovered it in 1861 with a spectroscope and named it after the bright red lines in its spectrum.

Discovery timeline