rubidium

• Description
• General information
• Physical data
• Radii
• Electronegativities
• Solid state structure
• Temperatures
• Enthalpies
• Ionization Enthalpies
• Isotopes
• Further information

Description

Rubidium can be liquid at ambient temperature, but only on a hot day given that its melting point is 40°C. It is a soft, silvery-white metallic element of the alkali metals group (Group 1) and it is the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, caesium, sodium, and potassium. It colours a flame yellowish-violet.

General information

Discoveror: Robert Bunsen, Gustav Kirchhoff
Date discovered: 1861
Discovered at: Germany
Meaning of name: From the Latin word "rubidius" meaning "deepest red"

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m^-3: 1532
Molar volume/cm³: 55.76

Radii /pm

Atomic: 265
Covalent (single bond):
Pauling radius for the ion [Rb]^-: no data

Valence shell orbital radius maxima (R_max)

orbital	s	p	d	f
radius	249.0	no data	no data	no data

Electronegativities

Both values are quoted on the Pauling scale.

Pauling: 0.82
Allred Rochow: 0.89

Crystal Structure

structure: bcc (body-centred cubic)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.

Temperatures (/K)

melting point: 312.46
boiling point: 961

Enthalpies /kJ mol^-1

fusion: 2.19
vaporization: 69.2

single bond enthalpies:

Rb-F	Rb-Cl	Rb-Br	Rb-I	Rb-Rb
490	444	385	331	45.6

Ionization enthalpies /kJ mol^-1

Number	Enthalpy
1st	403.0
2nd	2633
3rd	3900
4th	5080
5th	6850
6th	8140
7th	9570
8th	13100

Isotopes

This section gives some data for naturally occurring isotopes.

Nominal mass	Accurate mass	% natural abundance
85Rb	84.911794 (3)	72.165 (20)
87Rb	86.909187 (3)	27.835 (20)

Further Information

• Additional information about WebElements 1.2.2
• This is a licensed copy (here is the full list) of WebElements 1.2.2 and contains a subset of the material contained within the main version of WebElements (version 2)
• For further information please try WebElements version 2
• Sheffield Chemdex: perhaps the largest internet chemistry directory
• Sheffield Chemputer: interactive chemistry calculators on the WWW