Rubidium

Rubidium - Strontium
K Rb Cs
	Full table

General

Name, Symbol, Number

Rubidium, Rb, 37

Series

Alkali metals

Group, Period, Block

1(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 level

2, 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

Miscellaneous

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)

1^st ionization potential

403.0 kJ/mol

2^nd ionization potential

2633 kJ/mol

3^rd ionization potential

3860 kJ/mol

4^th ionization potential

5080 kJ/mol

5^th ionization potential

6850 kJ/mol

6^th ionization potential

8140 kJ/mol

7^th ionization potential

9570 kJ/mol

8^th ionization potential

13120 kJ/mol

9^th ionization potential

14500 kJ/mol

10^th ionization potential

26740 kJ/mol

Most Stable Isotopes

iso	NA	half-life	DM	DE M eV	DP
⁸⁵Rb	72.168%	Rb is stable with 48 neutrons
⁸⁷Rb	27.835%	4.7 × 10¹⁰ y	beta^-	0.283	⁸⁷Sr

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)

Applications

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:

As a working fluid in vapor turbines.
As a getter in vacuum tubes.
As a photocell component.
In the making of special glasses.
RbAg₄I₅ has the highest room conductivity of any known ionic crystal. This property could be useful in thin film batteries and in other applications.
Also considered for use in a thermoelectric generator using the magnetohydrodynamic principle where rubidium ions are formed by heat at high temperature and passed through a magnetic field. These conduct electricity and act like an armature of a generator thereby generating an electric current.

History

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.

Occurrence

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.

Isotopes

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.

Precautions

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.