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Rubidium - Strontium

Full table
Name, Symbol, NumberRubidium, Rb, 37
Series Alkali metals
Group, Period, Block1(IA), 5 , s
Density, Hardness 1532 kg/m3, 0.3
Appearance silvery white
Atomic Properties
Atomic weight 85.4678 amu
Atomic radius (calc.) 235 (265) pm
Covalent radius 211 pm
van der Waals radius 2.44
Electron configuration [Kr]5s5s1
e- 's per energy level2, 8, 18, 8, 1
Oxidation states (Oxide) 1 (strong base)
Crystal structure Cubic body centered
Physical Properties
State of matter solid
Melting point 312.46 K (102.76 F)
Boiling point 961 K (1270 F)
Molar volume 55.76 ×1010-3 m3/mol
Heat of vaporization 72.216 kJ/mol
Heat of fusion 2.192 kJ/mol
Vapor pressure (312.6 K) 1.56 × 10-4 Pa
Speed of sound 1300 m/s at 293.15 K
Electronegativity 0.82 (Pauling scale)
Specific heat capacity 363 J/(kg*K)
Electrical conductivity 7.79 106/m ohm
Thermal conductivity 58.2 W/(m*K)
1st ionization potential 403.0 kJ/mol
2nd ionization potential 2633 kJ/mol
3rd ionization potential 3860 kJ/mol
4th ionization potential 5080 kJ/mol
5th ionization potential 6850 kJ/mol
6th ionization potential 8140 kJ/mol
7th ionization potential 9570 kJ/mol
8th ionization potential 13120 kJ/mol
9th ionization potential 14500 kJ/mol
10th ionization potential 26740 kJ/mol
Most Stable Isotopes
isoNAhalf-life DMDE MeVDP
85Rb72.168%Rb is stable with 48 neutrons
87Rb27.835%4.7 × 1010 ybeta-0.28387Sr
SI units & STP are used except where noted.
Rubidium is a chemical element in the periodic table that has the symbol Rb and atomic number 37. Rb is a soft, silvery-white metallic element of the alkali metal group. Rb-87, a naturally occurring isotope, is (slightly) radioactive. Rubidium is highly reactive, with properties similar to other elements in group 1, like igniting spontaneously in air.

Table of contents
1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 Isotopes
6 Precautions
7 External Links

Notable Characteristics

Rubidium is the second most electropositive of the alkaline elements and can be a liquid at room temperature. Like other group 1 elements this metal ignites spontaneously in air and reacts violently in water, liberating and sometimes igniting hydrogen. Also like other alkali metals, it forms amalgams with mercury and it can form alloys with gold, caesium, sodium, and potassium. The element gives a yellowish violet color to a flame. (Hence its name)


Rubidium can be easily ionized, and because of this has been considered for use in ion engines for space vehicles (but caesium and xenon are more efficient for this purpose). Other potential or current uses:


Rubidium (
L rubidus, deepest red) was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff in the mineral lepidolite through the use of a spectroscope. However this element had minimal industrial use until the 1920s. Historically, the most important use for rubidium has been in research and development, primarily in chemical and electronic applications.


This element is considered to be the 16th most abundant element in the
earth's crust. It occurs naturally in the minerals leucite, pollucite, and zinnwaldite, which contains traces of up to 1% of its oxide. Lepidolite contains 1.5% rubidium and this is the commercial source of the element. Some potassium minerals and potassium chlorides also contain the element in commercially significant amounts. One notable source is also in the extensive deposits of pollucite at Bernic Lake, Manitoba. Rubidium metal can be produced by reducing rubidium chloride with calcium among other methods. Rubidium forms at least four oxides: Rb2O, Rb2O2, Rb2O3, RbO2. In 1997 the cost of this metal in small quantities was about US 25/gram.


There are 24 isotopes of rubidium known with naturally occurring rubidium being composed of just two isotopes; Rb-85 (72.2%) and the radioactive Rb-87 (27.8%). Normal mixes of rubidium are radioactive enough to expose photographic film in approximetely 30 to 60 days.

Rb-87 has a a half-life of 48.8 x 109 years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. Rb has been used extensively in dating rocks; Rb-87 decays to stable strontium-87 by emission of a negative beta particle. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr-87/Sr-86 ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See Rubidium-Strontium dating for a more detailed discussion.


Rubidium reacts violently with water and can cause fires. To ensure both safety and purity, this element must be kept under a dry mineral oil, in a vacuum or in an inert atmosphere.

External Links