The most reactive metals are the elements of groups I and II, located on the left side of the periodic table. A metal is considered reactive when it reacts strongly and rapidly with other elements. A metal's reactivity increases as we move from the top to the bottom of the periodic table.
The exception is hydrogen, which is not considered a metal and is located in the upper left corner of Mendeleev's periodic table of chemical elements.
The most active metals in the world
According to their reactivity, the metallic elements listed in the periodic table of chemical elements are divided into three groups:
- Active metals.
- Medium activity metals.
- Low-activity metals.
The most active metals on Earth are lithium, cesium and francium.
Cesium is the most reactive of the non-radioactive elements. It is a rare, silvery-yellow, lustrous metal with an atomic number (the number of protons in the nucleus) of 55. It is a very soft element that will melt in your hands—if it doesn't explode first, as it reacts strongly to moisture.
There's also a highly radioactive element, francium, which may be more reactive than cesium. Whether it's not, we'll probably never know, because francium is not only extremely radioactive but also an extremely rare metal.
The last of the three most reactive metals, lithium, has an interesting property: it imparts a crimson color to flames.
Here is a video demonstration of the activity of lithium, sodium, potassium, rubidium and cesium.
What is cesium?
Cesium is an alkali metal. It is highly reactive and does not occur naturally. These metals are also highly ductile and are good thermal and electrical conductors.
Cesium was the first element detectable with a spectroscope. It was discovered in 1860 by German chemists Robert Bunsen and Gustav Kirchhoff while analyzing the spectrum of mineral water from the Bad Dürkheim spring.
Cesium occurs naturally in the minerals pollucite and lepidolite. It is also found in many aluminosilicates, such as beryl, petalite, and carnallite. The richest known cesium deposit is located in Canada, on the shores of Bernic Lake. It contains approximately 701 TP3T of all Earth's reserves. Interestingly, this lake is the site of an annual Cesium Festival (February 24), when tons of the substance are burned in snow, and other cesium madness prevails.
Cesium is also a byproduct of nuclear fission in reactors.
Properties of cesium
Although cesium is not the heaviest metal in the world, it is the most active and has a number of unique properties:
- It burns spontaneously in air and explodes instantly on contact with water or moisture in any form, even ice down to -116 C.
- It burns with a brilliant blue flame. To the uninitiated, the flame appears purple rather than blue, but with sufficient meditation, study of chemistry, and blissful hours spent in awe of cesium burning, the true blue nature of its flame is revealed.
- The name "cesium" comes from the two bright blue lines in its emission spectrum. Translated from Latin, "caesius" means "sky-blue.".
- Its hydroxide (liquid molten state) can eat through flesh, glass, and many other substances. Only rhodium metal and several of its alloys can withstand molten cesium hydroxide.
- Cesium iodide and bromide are used as core components in the production of high-precision optics, including night vision scopes, goggles, and binoculars. Cesium has also been experimentally used in ion propulsion systems for spacecraft due to its low ionization potential.
- Cesium is used to create the most accurate atomic clocks. Even the best wristwatches in the world can lose several seconds or even a minute. But cesium-based atomic clocks lose only one second every five billion years.
- Natural cesium consists of one stable isotope, Cs-133. Thirty other radioactive isotopes are known, ranging from Cs-114 to Cs-145. Cesium-137 (also known as radiocesium) is one of the most biologically hazardous components of radioactive waste and nuclear fallout. It accumulates in living organisms and even in fungi, and the highest levels are found in reindeer and waterfowl in North America.
Humans and animals are constantly exposed to minute amounts of cesium through eating, breathing, and drinking. While it's unlikely that we'll become ill from cesium alone, prolonged exposure can lead to adverse health effects, including nausea, vomiting, bleeding, and cell damage.
Cesium and cancer treatment
Paracelsus even claimed that everything is poison, and everything is medicine. It's all a matter of dosage. And when it comes to cesium, Paracelsus's words are absolutely true.
Cesium's effectiveness in treating several forms of cancer, including brain tumors, is currently being studied. Cesium-131, a radioactive isotope of cesium, is placed in a brachytherapy capsule ("seed") along with another radioactive isotope (iodine-125).
According to the American Society of Brachytherapy, a brachytherapy capsule is a radioactive "pod" that is placed directly into cancerous tissue. These seeds are effective against several forms of cancer, including prostate, cervical, and endometrial cancer.
In one study, a group of 24 patients with brain tumors were implanted with cesium-131 brachytherapy seeds. Minimal side effects were noted, and overall, patients tolerated this form of treatment well.
The idea of using cesium-131 brachytherapy seeds as a cancer treatment arose as early as the 1960s and was described in a study published in the journal Radiology. A 2009 study published in the journal Medical Physics discussed the use of cesium-131 seeds for the treatment of prostate cancer, with positive results.
More research is needed before cesium therapy can be firmly established in medicine. However, so far, research shows that the use of cesium-131 in the treatment of cancer tumors via brachytherapy is promising.
Comparison of cesium and francium
Like cesium, francium (Fr) is an alkali metal (only radioactive) and has extremely high chemical activity.
- The density of francium is 1.87 grams per cubic centimeter, which is comparable to the density of cesium - 1.879 grams per cubic centimeter.
- Cesium and francium are two of four metals that are liquid at room temperature. Mercury and gallium also exhibit this property.
- Cesium reacts with water quite spectacularly, explosively, forming cesium hydroxide (CsOH) and hydrogen gas (H2). Francium and water also don't particularly like each other, and when they react, they form the strongest alkali—francium hydroxide.
- Like cesium, francium accumulates in living organisms. Therefore, its isotopes have found application in medicine, cancer diagnostics, and various biological research.
- In terms of abundance, cesium far exceeds francium. About 20 tons of enriched cesium ore are mined worldwide annually. According to PeriodicTable, cesium is the 50th most abundant element in the Earth's crust. Francium, on the other hand, accounts for about 340 grams of the Earth's crust.
That is, in terms of their properties, the two most active metals on the planet are very similar.
Comparisons of cesium and lithium
Lithium is one of the top three most reactive metals on the planet. It is a key component in batteries that power smartphones, laptops, and electric vehicles. More than half of the world's lithium supplies come from the "Lithium Triangle"—Bolivia, Chile, and Argentina. The largest source of lithium from salt is Chile's Atacama Desert.
- Like cesium, lithium is an alkali metal. And, like cesium, it occurs in nature only as compounds. However, traces of lithium are found in almost all igneous rocks and in many mineral springs. It was one of the three elements created in the Big Bang, along with hydrogen and helium.
- There is little lithium and cesium in the earth's crust - 21 g/t and 3.7 g/t, respectively.
- While cesium ignites in air when exposed to oxygen, lithium can even be stored outdoors for some time. This "tolerance" makes lithium the only alkali metal that does not require storage in kerosene. It can also ignite when exposed to oxygen, but only at high temperatures.
- Lithium is the least dense metal (0.533 g/cm³). Cesium is much denser—1.879 grams per cubic centimeter. Lithium's lightness means it can store energy without adding weight to devices.
- However, lithium gives cesium a run for its money in terms of low melting point. Its melting point is 180.5 degrees Celsius, while cesium melts at 28.4 degrees Celsius.
- However, lithium boils quickly – at 134 degrees, while bringing cesium to a boil is not easy; a temperature of 678 degrees is required.
- Both lithium and cesium are easily cut with a regular knife.