Radium (Ra), atomic number 88, is a rare element known primarily for its intense radioactivity. It resides in Group 2 of the periodic table, classifying it as an alkaline earth metal alongside elements like magnesium and calcium. In its pure form, radium is a lustrous, silvery-white metal, although it quickly reacts with nitrogen in the air to form a black surface layer of radium nitride.
The most stable and common isotope is Ra-226, which possesses a half-life of approximately 1,600 years. This long half-life means that Ra-226 is a naturally occurring intermediate product in the decay chain of uranium-238. Radium’s decay involves the continuous emission of alpha, beta, and gamma radiation, making its handling extremely hazardous. This decay also produces radon-222, a radioactive gas that requires careful ventilation when the element is stored.
Defining the Boiling Point of Radium
For radium, the accepted boiling point is often cited as an estimate, reflecting the difficulty of its measurement. The most commonly accepted value places the temperature at 1737°C (3159°F) at standard pressure.
This figure is slightly lower than the boiling point of its lighter congener, barium, which is consistent with general periodic trends observed in the alkaline earth metals. However, other values, such as 1140°C or 1500°C, have been suggested in various technical sources, underscoring the uncertainty surrounding the precise value.
Difficulties in Measuring Radium’s Physical Constants
Radium’s physical constants, including its boiling point, are often estimates due to the element’s inherent properties and the methodological challenges of high-temperature measurement. Radium is intensely radioactive, resulting in self-heating. A sample continuously emits energy from its decay, causing it to maintain a temperature higher than its surroundings.
This internally generated heat complicates accurate temperature readings during a phase transition experiment, as the measured temperature is a combination of external heating and internal radioactive energy release. Furthermore, the constant emission of highly energetic alpha, beta, and gamma radiation requires specialized, heavily shielded equipment and extreme safety precautions. The intense radiation causes chemical changes in the measuring apparatus, which can introduce significant experimental error.
The limited availability of pure radium samples adds another layer of complexity. Radium occurs only in trace amounts within uranium ores, and its purification is an expensive and difficult task. Measuring the boiling point requires a substantial, pure sample to ensure consistent vaporization. The extreme toxicity and the continuous generation of radioactive radon gas demand that all experiments be conducted in closed, ventilated systems, restricting the types of apparatus that can be used for direct measurement.
Related Physical Properties of Radium
At room temperature, radium is a solid with a moderately high density, typically cited as 5.5 g/cm³. This places it among the heavier alkaline earth metals, with a density significantly higher than that of its predecessor in the group, barium.
The melting point (MP) of radium is another physical constant that is sometimes disputed, but the most frequently cited value is 700°C (1292°F). Some sources suggest a higher melting point, but the 700°C value aligns with the general trend of decreasing melting points down Group 2. The combination of its high melting and boiling points confirms that radium is a non-volatile metal, requiring high temperatures to change its physical state.