Caesium is a chemical element in the Periodic Table marked with an atomic number of 55 and with the chemical symbol Cs. This chemical element is an Alkali Metal and like all Alkali Metals, it belongs to group 1 elements in the Periodic Table. Caesium is so soft that it’s one of the few chemical elements, which have a natural liquid state at room temperature.


Caesium shares various group trends in terms of physical and chemical properties compared to the rest of the Alkali Metal elements. This element has a silvery-gold hue and it is quite ductile and reactive to water, air and other chemical elements. Apart from the fact that it is highly reactive, Caesium is also extremely pyrophoric. This Alkali Metal element can various anions and it also forms intermetallic compounds with Thorium, Indium, Antimony, Gallium, and the rest of the Alkali Metals excluding Lithium. Due to its high reactivity this particular element is classified among the most hazardous materials. Caesium’s melting and boiling points are quite low and it can only be stored in hermetically sealed containers made out of borosilicate glass.


Physical Characteristics of Caesium

Like all Alkali Metals Caesium is soft and ductile, and has a silvery-gold metallic hue in terms of color and physical appearances. Caesium has a significantly low density similar to most metals. Because of its extremely low melting and boiling points this group 1 element can be found in liquid state at room temperature. It has the second lowest melting point of any metal after Mercury. When Caesium is subjected to a flame test, it transforms the flame’s color into violet or blue. It may appear in a solid natural state in an environment with a temperature lower than 28C.


Chemical Properties of Caesium


Atomic Number – 55

Group – 1

Period – 6

Block – s

Electronic Configuration – 6s1

Relative Atomic Mass – 132.905 (132.9054 g/mol)

Molecular Weight – 132.905

Electronegativity – 0.79

Density (G CM-3) – 1.93 g/cm3 at room temperature, 1.843 g/cm3 in liquid state

Melting Point –   301.7 K; 28.5 °C; 83.3 °F

Boiling Point – 944 K; 671 °C; 1240 °F

Atomic Radius – 265pm

Isotopes – 40

Electronic Shell – 2, 8, 18, 18, 8, 1


Discovery of Caesium

Back in 1960 two German scientists, named Robert Bunsen and Gustav Kirchhoff, managed to discover a new Alkali Metal element. What they did was to examine the new element they found in Durkheim’s mineral waters under their brand new spectroscope – a device, which they had invented the previous year. They decided to name the newly found chemical element after the Latin word for sky-blue color – Caesius, because of the significant blue hues the element was showing under the spectroscope. The very first successful and thorough isolation of Caesium was done by Carl Setterberg in 1882.


Recognized by:   Robert Bunsen and Gustav Kirchhoff (1860)

Known and discovered by: Robert Bunsen and Gustav Kirchhoff (1860)

Named by: Robert Bunsen and Gustav Kirchhoff


Uses and role of Caesium

Caesium has various uses and applications in a number of industries, including glass manufacturing, atomic clocks, metallurgy, telecommunication, and electronics.


Caesium compounds can be found in the extremely accurate atomic clocks, which play a key role in any GPS system. It is also used in metallurgy because of its high reactivity, in the construction industry and also for drilling fluids for the oil industry. Caesium plays various roles in many electronics because of its photoemissive properties, which are applied in video camera tubes. This Alkali Metal element also plays a significant role in lasers, lamps, magnetometers, various medicines, and even in acrylic paint.


Caesium on Earth

Caesium is not only considered as an incompatible element because of its large ionic radius, but it’s also rare on Earth. It is mostly abundant in some minerals, like carnallite, but it mostly exists in pegmatite ores. The biggest Caesium resource is found in Bernic Lake, Canada, where nearly 2/3 of the entire Caesium abundance on Earth is stored.



Excessive Caesium dosage in living organism can lead to various health related issues, including arrhythmia, hypokalemia, and even a cardiac arrest. However, some Caesium salts have been tested as anti-shock agents as ways of the human body to cope with the administering of arsenical drugs. However, Rubidium or Potassium salts are more likely to be used as such anti-shock agents because they are less harmful to the human heart.