Molecular structure:

IUPAC Name: Cesium 
Synonyms of Cesium (CAS NO.7440-46-2): Cesium-133 ; Cesium Aa Single Element Standard ; Cesium, Aas Standard Solution ; Cesium Aa Standard ; Cesium Atomic Absorption Standard ; Cesium Atomic Spectroscopy Standard ; Cesium ; Cesium Metal 
Product Categories: Alkali Metals Metal and Ceramic Science ; Cesium ; Metals ; Reduction ; Synthetic Reagents
Molecular Formula: Cs
Molecular Weight: 132.91
EINECS: 231-155-4 
Density: 1.873 g/mL at 25 °C 
Melting Point: 28.5 °C
Boiling Point: 705 °C
Vapor pressure: 1 mm Hg ( 279 °C)
Storage temp.:  2-8°C
Solubility in H₂O: soluble
Merck: 13,2018
Stability: Flammable solid; highly flammable in powder form. Moisture-sensitive. Incompatible with chlorine, phosphorus, water.

  Cesium (CAS NO.7440-46-2) (Latin caesius meaning "bluish gray") was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water from Dürkheim, Germany, as described below. Carl Setterberg first produced caesium metal in 1882 by electrolysis of caesium chloride.Setterberg received his PhD from Kekule and Bunsen for this work.
Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical fields. It found no significant application until its was added into radio vacuum tubes in the 1920s as a getter, a scavenger of the trace amounts of oxygen remaining in the tube after manufacture, and as a coating on the heated cathode to increase the amount of electric current that could flow through the tube. Caesium became recognized as a functional, high-performance industrial metal in electronics in the 1950s.
Since 1967, the International System of Measurements has based its unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as 9,192,631,770 cycles of the radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the 133Cs atom.

Raw materials is Argon .
Most of the mined Cesium (CAS NO.7440-46-2) is directly converted into caesium formate (HCOO⁻Cs⁺) for applications such as oil drilling. Caesium metal can be isolated by electrolysis of fused caesium cyanide. Exceptionally pure and gas-free caesium can be made by the thermal decomposition of caesium azide. In vacuum applications, caesium dichromate can be reacted with zirconium forming pure caesium without other gaseous products.
Cs₂Cr₂O₇ + 2 Zr → 2 Cs + 2 ZrO₂+ Cr₂O₃ The primary commercial compounds of caesium are caesium chloride and its nitrate.

Reported in EPA TSCA Inventory.

Moderately toxic by intraperitoneal route. Cesium is quite similar to potassium in its elemental state. It has been shown, however, to have pronounced physiological action in experimentation with animals. Hyper-irritability, including marked spasms, has been shown to follow the administration of cesium in amounts equal to the potassium content of the diet. It has been found that replacing the potassium in the diet of rats with cesium caused death after 10–17 days. Ignites spontaneously in air. Violent reaction with water, moisture, or steam releases hydrogen gas which explodes. Violent reaction with acids, halogens, and other oxidizing materials. Incandescent reaction with nonmetals (e.g., sulfur, phosphorus). See also SODIUM. 
Hazard Codes:Xi,C,F+
Risk Statements of  Cesium (CAS NO.7440-46-2):
R36/38:Irritating to eyes and skin. 
R34:Causes burns. 
R14/15: Reacts violently with water and contact with water liberates extremely flammable gases. 
R11:Highly flammable.
Safety Statements:
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
S45:In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S43:In case of fire use ... (there follows the type of fire-fighting equipment to be used.) 
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection. 
S16:Keep away from sources of ignition. 
S8:Keep container dry.
RIDADR: UN 3264 8/PG 3
WGK Germany: 3
RTECS: FK9225000
F 10: Keep under argon.
HazardClass: 4.3
PackingGroup: I

DOT Classification:  4.3; Label: Dangerous When Wet

 Cesium (CAS NO.7440-46-2) is a silvery, light ductile metal. It causes burns to skin and eyes.It is highly flammable.Reacts violently with most acids. Reacts violently with fluorine, chlorine, bromine and iodine. Reacts with incandescence with sulfur and phosphorus. Burns vigorously in air.Inhalation or contact with vapors, substance or decomposition products may cause severe injury or death. May produce corrosive solutions on contact with water. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control may cause pollution.Produce flammable gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Runoff may create fire or explosion hazard.