Radium is a chemical element with the symbol Ra and atomic number 88. It is an alkaline earth metal and is the heaviest of the alkaline earth metals. Radium was discovered in 1898 by Marie and Pierre Curie from a uranium ore called pitchblende. The name “radium” comes from the Latin word “radius,” meaning “ray,” reflecting its ability to emit energy in the form of rays. The name reflects the high levels of radioactivity emitted by the element.
Basic Radium Facts
- Name: Radium
- Atomic Number: 88
- Element Symbol: Rn
- Atomic Mass: 
- Element Group: Group 2 (alkaline earth metals)
- Period: Period 7
- Block: s-block
- Electron Configuration: [Rn] 7s2
- Appearance: Solid silvery metal
Discovery of Radium
The discovery of radium traces back to the pioneering work of Marie Curie along with her husband Pierre Curie. Their journey began with the investigation of the mineral pitchblende, which is rich in uranium, and led to the groundbreaking discovery of radioactivity.
- Uranium Rays: In 1896, Henri Becquerel discovered that uranium salts emitted rays that could fog photographic plates, similar to X-rays discovered by Wilhelm Roentgen. Marie Curie began her doctoral research by exploring these “uranium rays.”
- Marie Curie’s Research: Marie’s systematic studies revealed that the rays were not the outcome of a chemical reaction but were coming from the atom itself. This was a revolutionary concept at the time, as atoms were thought to be indivisible.
- Pitchblende Studies: The Curies found that pitchblende, despite having its uranium removed, was more radioactive than uranium itself. They hypothesized that pitchblende contained other radioactive elements.
- Isolation of Polonium and Radium: In 1898, the Curies announced the discovery of two new elements: polonium, named after Marie’s native Poland, and radium, from the Latin “radius” meaning “ray.”
- Challenges and Triumph: The process of isolating radium was arduous. It took the Curies four years of processing tons of pitchblende to isolate a tiny amount of radium chloride, proving the existence of radium. Marie Curie first isolated a pure sample in 1910.
- Nobel Prize: The discovery of radium and polonium, and the subsequent research on radioactivity, led to the Curies being awarded the Nobel Prize in Physics in 1903, shared with Henri Becquerel.
Appearance and Properties
- Appearance: Pure radium is a silvery-white metal.
- Physical Properties: It is highly radioactive and its most stable isotope, Ra-226, has a half-life of about 1,600 years. Radium glows in the dark due to its intense radioactivity, which it imparts to other substances.
Radium has 33 isotopes, ranging in mass number 202 to 234. All of the isotopes of radium are radioactive. Of these, Ra-226 and Ra-228 are the most common. Ra-226 arises from the decay of uranium, while Ra-228 derives from thorium and uranium decay. Ra-226 has the longest half-life of the isotopes (1600 years).
Abundance and Sources
Radium occurs in tiny amounts in uranium ores. It is extremely rare, making up about 1 part per trillion of the Earth’s crust. Its rarity and radioactivity make its extraction and handling quite challenging and expensive.
Uses of Radium
Historically, radium found use in radioluminescent paint and for numerous quack medical cures. It still finds use in medicine today, but mostly the element’s importance is in research.
- Medical: Previously, radium was used for make radon gas for use in radiotherapy for cancer treatment. Today, radium-223 has an approved use as a bone cancer treatment.
- Industrial: Used in radioluminescent devices like clocks, watches, and aircraft instruments.
- Scientific Research: Radium finds use in radiation research. It induces mutations, so is useful for studying genetics. It has limited use in industrial radiography for imaging metallic parts and as a neutron source. Most research involving radium involves optical, atomic, and molecular physics, as in the development of optical clocks.
Radium typically exhibits a +2 oxidation state. This is its most stable and common state, similar to other alkaline earth metals.
Biological Role, Health Effects, and Toxicity
Radium has no biological role in any organism. It is highly toxic due to its radioactivity. Exposure causes harmful health effects, including radiation sickness, anemia, and cancer. Safety protocols are critical when handling radium or radium-containing materials.
Table of Key Radium Facts
|Atomic Weight||≈ 226 u|
|Group||2 (alkaline earth metals)|
|Electron Configuration||[Rn] 7s²|
|Electrons Per Shell||2, 8, 18, 32, 18, 8, 2|
|State at Room Temperature||Solid|
|Melting Point||700°C (973 K) (estimated)|
|Boiling Point||1737°C (2010 K)|
|Density||≈ 5 g/cm³|
|Heat of Vaporization||113 kJ/mol|
|Heat of Fusion||8.5 kJ/mol|
|Oxidation States||+2 (main)|
|Ionization Energies||1st: 509.3 kJ/mol, 2nd: 979.0 kJ/mol|
|Covalent Radius||221 pm|
|Van der Waals Radius||283 pm|
|Crystal Structure||body-centered cubic (bcc)|
Interesting Radium Facts
- Luminous Paint: Many people alive today remember radium-based self-luminous paints for watches, aircraft dials, and other instruments. The term “radium girls” refers to the workers who applied the paint and later suffered from radium poisoning.
- Not-So-Distant Past: Radium use remained common well into the 20th century. For example, physicians administered radium-laced nasal irrigation to children with inflamed tonsils or ear infections from the late 1940s through the early 1970s in the US.
- Commercial Elixirs: In the early 20th century, radium was a key ingredient in various health products, including tonics and cosmetics.
- Radium Spas: Places with radium-rich water, like the famous spa town of Bad Gastein in Austria, became popular for “radon therapy,” where people bathed in the radioactive waters for therapeutic purposes. The natural radium decayed into radon gas.
- Radium as a Heater: Radium emits heat continuously due to its radioactive decay. It was this property that enabled the Curies to isolate it, as the heat provided a way to track the substance’s presence.
- Medical Pioneering: Radium was one of the first radioactive elements used in brachytherapy, a type of radiotherapy where a sealed radiation source is placed inside or next to the area requiring treatment.
- Radium’s Luminescence: Radium glows pale blue-green in the dark from its radiation ionizing nitrogen and oxygen in air. However, the green glow commonly associated with the element actually comes from the phosphor used in radioluminescent paint. The radiation excites the electrons in doped zinc sulfide, which then emits green light.
- Radium’s Fading Glow: The glowing paint that contained radium does not glow anymore. The radium remains radioactive, but over time this extreme radioactivity damages the phosphor.
- Prestigious Collectible: Due to its historical significance and rarity, old radium-based watch dials and equipment are valuable collector’s items, despite their radioactivity.
- Nuclear Transmutation: Radium was involved in the first successful demonstration of artificial nuclear transmutation in 1919. Ernest Rutherford used alpha particles emitted by radium to convert nitrogen into oxygen.
- Red Flames: While it’s not a great candidate for the flame test because of its radioactivity, radium and its compounds color fire red.
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