Polonium is a rare, highly radioactive element whose physical properties are profoundly influenced by its intense nuclear activity. The temperature at which this substance transitions from a liquid to a gas is approximately 962 degrees Celsius. This boiling point is foundational for understanding the element’s behavior and extreme volatility. Scientists must account for polonium’s inherent instability when defining its thermal characteristics accurately.
The Numerical Boiling Point and Melting Point
The accepted standard boiling point for polonium is \(962^\circ\text{C}\). This temperature is equivalent to \(1,764^\circ\text{F}\) or \(1,235 \text{K}\). This temperature represents the point where the element’s vapor pressure equals the surrounding atmospheric pressure, allowing a phase transition from liquid to gas.
The melting point of polonium provides a lower thermal boundary for its liquid range. Polonium becomes liquid at \(254^\circ\text{C}\), or \(489^\circ\text{F}\). This relatively low melting point, combined with a boiling point nearly \(700^\circ\text{C}\) higher, defines a significant temperature range where the element exists as a liquid. However, its behavior within this liquid range is complicated by its own internal heat generation.
Defining Polonium: An Overview of the Element
Polonium, symbolized as Po, occupies position 84 on the periodic table. It is found in Group 16, known as the chalcogens, alongside elements like sulfur and tellurium. While sometimes classified as a metalloid, polonium exhibits many properties of a metal.
The element’s discovery is credited to Marie and Pierre Curie in 1898. They isolated polonium from the uranium ore pitchblende, identifying it solely by its powerful radioactivity. Marie Curie named the element after her native country, Poland, which was not an independent nation at the time.
Polonium exists in nature only in trace amounts, primarily as a short-lived intermediate in the decay chain of uranium. It has no stable isotopes; all known forms are radioactive. The most commonly studied isotope is polonium-210, which is typically produced artificially in nuclear reactors.
Polonium’s Volatility Driven by Radioactive Decay
The intense radioactivity of polonium-210 significantly complicates its physical measurements, including the determination of its boiling point. Polonium-210 decays by emitting alpha particles (helium nuclei). This process releases a tremendous amount of energy, which is absorbed by the surrounding material as heat.
The energy released is so substantial that a single gram of polonium-210 generates approximately \(140\) watts of thermal power. This radioactive self-heating causes a pure sample of polonium to spontaneously heat up to temperatures exceeding \(500^\circ\text{C}\). This means the element is constantly close to, or well above, its melting point without any external heat source.
This continuous self-heating makes precise, standard thermophysical measurements difficult because the sample’s temperature is constantly changing. The intense energy output creates a high vapor pressure, making polonium-210 a highly volatile substance. Its volatility is demonstrated by the fact that \(50\%\) of a polonium-210 sample will vaporize in air in just \(45\) hours, even at a temperature as low as \(55^\circ\text{C}\).
The sample effectively vaporizes itself well below the theoretical \(962^\circ\text{C}\) boiling point. This extreme volatility is the primary reason polonium presents a unique hazard, as it can easily spread through the air as a gas or fine aerosol. The measured boiling point of \(962^\circ\text{C}\) is a theoretical value for pure, non-self-heating polonium, but its radioactive nature means it behaves like a much more volatile substance in practice.