Courses
What is Cesium?
By Brijesh Sharma
|
Updated on 23 Apr 2025, 16:00 IST
Cesium (also spelled Caesium in British English) is a soft, silvery-golden metal that belongs to the alkali metal group on the periodic table. It is known for being highly reactive, especially with water, and is one of the few metals that can be liquid at room temperature. Cesium has the chemical symbol "Cs" and an atomic number of 55.
This element is not only important in chemistry but also plays a big role in many industries. It is used in atomic clocks, oil drilling, medicine, and even in space technology. Cesium is also found in modern technology through tools like CesiumJS, which helps create 3D maps and virtual globes on the internet.
In this article, we will explore what cesium is, its symbol, electron configuration, uses, where it appears on the periodic table, and other interesting facts like whether cesium is radioactive. We'll also cover where to buy cesium metal, what it's used for, and the difference between cesium and caesium.
Whether you are a student, a science enthusiast, or just curious about elements, this guide will help you learn everything you need to know about cesium in a simple and clear way.
What is Cesium?
Cesium (also spelled caesium in British English) is a soft, silvery-golden alkali metal. It is one of the most reactive chemical elements and reacts explosively with water. Cesium is known for its low melting point of just 28.5 °C (83.3 °F), which means it can be liquid at room temperature in warm environments. It was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff through the flame spectroscopy technique.
Cesium Symbol and Atomic Number
| Property | Value |
| Chemical Symbol | Cs |
| Atomic Number | 55 |
| Atomic Mass | 132.91 u |
| Group | Alkali Metals (Group 1) |
| Period | 6 |
| Block | s-block |
| Density | 1.93 g/cm³ |
| Melting Point | 28.5 °C |
| Boiling Point | 671 °C |
The symbol for cesium is "Cs", and it is placed in Group 1 (alkali metals) of the periodic table, which includes other reactive metals like lithium, sodium, and potassium.
Loading PDF...
Do Check - Latent Heat of Fusion
Cesium Electron Configuration
The electron configuration of cesium is:
[Xe] 6s¹
This means cesium has one valence electron in the outermost 6s orbital, which explains its high reactivity. It easily loses this single electron to form a +1 ion (Cs⁺) in chemical reactions.
Is Cesium Radioactive?
Naturally occurring cesium consists mostly of the stable isotope Cs-133, which is not radioactive. However, some isotopes like cesium-137 (Cs-137) are radioactive and are byproducts of nuclear fission reactions in nuclear power plants and weapons testing. Cs-137 is used in medical radiation therapy and industrial gauging equipment.
Cesium Element in the Periodic Table
Cesium is located in:
- Group 1 (IA) – Alkali metals
- Period 6
- Block s
Its position in the periodic table gives it characteristics such as:
- Highly reactive with water and air
- Forms strong bases (like cesium hydroxide)
- Easily ionized
Do Check - Propane
Cesium Uses
Cesium is a versatile element with many applications:
| Industry/Use | Application |
| Atomic Clocks | Cesium atomic clocks are the most accurate timekeepers in the world. |
| Oil Drilling | Cesium formate is used as a drilling fluid because of its high density. |
| Medicine | Radioactive isotopes like Cs-137 are used in cancer treatment. |
| Space Exploration | Cesium is used in ion propulsion systems in some spacecraft. |
| Photoelectric Cells | It helps convert light into electric current in light sensors. |
| Research & Development | Used in vacuum tubes and scientific experiments. |
Cesium Metal
Cesium metal is silvery-gold and soft, so soft that it can be cut with a butter knife. It is highly pyrophoric, meaning it can catch fire when exposed to air. Because of this, it is usually stored in sealed glass ampoules or under mineral oil to prevent dangerous reactions.
Precautions with Cesium:
- Must be stored safely to prevent fire
- Should not come into contact with water
- Requires careful handling under inert gases or mineral oil
Do Check - Vanadium
Cesium or Caesium?
Both spellings are correct:
- Cesium is used in American English
- Caesium is the British English spelling
The IUPAC officially adopted caesium as the name, but cesium remains more popular in scientific and commercial settings globally, especially in the U.S.
CesiumJS and Cesium Ion
Cesium is not just a chemical element—it also refers to CesiumJS, a popular open-source JavaScript library for creating 3D geospatial applications. It allows developers to build high-resolution 3D maps and virtual globes.
- CesiumJS is used in defense, aerospace, real estate, and urban planning.
- Cesium Ion is the cloud-based platform that provides global terrain data, imagery, and analytics for CesiumJS users.
Do Check - Polarity
Where to Buy Cesium?
You can buy cesium metal and cesium compounds from specialized chemical suppliers or online marketplaces. However, due to its reactive and hazardous nature, its purchase may require a proper license and safety compliance.
Popular cesium products available include:
- Cesium chloride
- Cesium nitrate
- Cesium formate
Note: Cesium is regulated in many countries due to its explosive potential and radioactive isotopes, so commercial availability is restricted.
Conclusion
Cesium is an extraordinary element—whether you're looking at it as a powerful alkali metal, a component in atomic clocks, or the backbone of modern 3D mapping software like CesiumJS. Its unique chemical and physical properties make it both fascinating and highly useful across various industries. But due to its reactivity and potential danger, it must be handled with extreme caution.
What is Cesium? FAQs
What is cesium and where is it found?
Cesium is a soft, silvery-golden metal that is highly reactive. It is mainly found in a mineral called pollucite, usually mined in Canada and other parts of the world.
What is the symbol and atomic number of cesium?
The symbol for cesium is Cs, and its atomic number is 55 on the periodic table.
What are the main uses of cesium?
Cesium is used in atomic clocks, medical radiation, oil drilling fluids, photoelectric cells, and spacecraft ion engines.
Is cesium dangerous or radioactive?
Natural cesium (Cs-133) is not radioactive. However, some isotopes like Cs-137 are radioactive and can be dangerous if not handled properly.
Why is cesium used in atomic clocks?
Cesium atoms vibrate at a precise frequency, which helps atomic clocks measure time with extreme accuracy, even better than regular quartz clocks.
Can you buy cesium metal online?
Yes, cesium can be bought from chemical suppliers, but due to its high reactivity, its sale is often regulated and requires special handling licenses.
What is the difference between cesium and caesium?
There is no chemical difference. “Cesium” is the American spelling, while “Caesium” is the British spelling. Both refer to the same element with the symbol Cs.