Cesium, symbolized as Cs, is a chemical element with the atomic number 55. It resides in the periodic table as a distinctive member of the alkali metals. This silvery-golden element possesses a unique set of characteristics that set it apart in the realm of metals.
Alkali Metal Classification
Cesium belongs to Group 1 of the periodic table, known as the alkali metals. Elements in this group share several general characteristics due to having a single electron in their outermost shell. Alkali metals are soft, highly reactive, and possess low melting points. They readily lose their single valence electron to form positively charged ions.
As one moves down Group 1, the atomic size increases, and the outermost electron is further from the nucleus, making it even easier to remove. Consequently, cesium, located towards the bottom of this group, exhibits enhanced reactivity compared to its lighter counterparts.
Unique Properties and Extreme Reactivity
Cesium is a soft metal that melts at approximately 28.5 °C (83.3 °F), meaning it can be liquid at or near room temperature. This low melting point makes it one of only a few elemental metals that exist in a liquid state under such conditions. Cesium also exhibits the highest electropositivity and among the lowest electronegativity of all stable elements.
The chemical reactivity of cesium is notably extreme. It is pyrophoric, meaning it spontaneously ignites when exposed to air, forming cesium superoxide. Its reaction with water is even more vigorous and highly exothermic, often resulting in an explosive outcome. This reaction produces cesium hydroxide and hydrogen gas, with the heat generated causing the hydrogen to ignite. Due to its extreme reactivity, cesium must be stored in inert environments, such as submerged in mineral oil or sealed in vacuum-tight containers, to prevent contact with air or moisture.
Practical Applications and Natural Occurrence
Despite its extreme reactivity, cesium has several specialized practical applications. It is relatively rare, occurring naturally in minerals like pollucite, with significant deposits found in regions such as Manitoba, Canada, and Zimbabwe. Its most renowned application is in atomic clocks, which utilize the precise microwave frequency of cesium-133 atoms to define the second with exceptional accuracy. These clocks are fundamental for global positioning systems (GPS), internet infrastructure, and mobile phone networks.
Cesium compounds, particularly cesium formate, are extensively used in the oil and gas industry as high-density, low-viscosity drilling fluids. These fluids help maintain wellbore stability in high-pressure, high-temperature drilling operations. Additionally, cesium is employed in photoemissive cells, where its low ionization energy allows it to readily emit electrons when exposed to light, converting light energy into electrical signals. Some radioactive isotopes of cesium, such as cesium-137, are used in medical radiation therapy for cancer treatment.