Krypton was one of three noble gases discovered in 1898 by Scottish chemist and physicist Sir William Ramsay (1852-1916) and English chemist Morris William Travers (1872-1961). Ramsay and Travers discovered the gases by allowing liquid air to evaporate. As it did so, each of the gases that make up normal air boiled off, one at a time. Three of those gases—krypton, xenon, and neon, were discovered for the first time this way.
The term noble gas refers to elements in Group 18 (VIIIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. These gases have been given the name "noble" because they act as if they are "too arrogant" to react with other elements. Until the 1960s, no compound of these gases was known. Since they are so inactive, they are also called the inert gases. Inert means inactive.
Group 18 (VIIIA)
Krypton has relatively few commercial uses. All of them involve lighting systems in one way or another.
Discovery and naming
By 1898, two members of the noble gas family had been discovered. They were helium (atomic number 2) and argon (atomic number 18). But no other elements in the family had been found. The periodic table contained empty boxes between helium and argon and below argon. The missing noble gases had atomic numbers 10, 36, 54, and 86. Chemists think of empty boxes in the periodic table as "elements waiting to be discovered."
Since the two known noble elements, helium and argon, are both gases, Ramsay and Travers hoped the missing elements were also gases. And if they were, they might be found in air. The problem was that air had already been carefully analyzed and found to be about 99.95 percent oxygen , nitrogen , and argon. Was it possible that the missing gases were in the last 0.05 percent of air?
To answer the question, the chemists worked not with air itself, but with liquid air. Air becomes liquid simply by cooling it far enough. The colder air becomes, the more gases within it turn into liquids. At -182.96°C (-297.33°F), oxygen changes from a gas into a liquid. At -195.79°C (-320.42°F), nitrogen changes from a gas into a liquid. And so on. Eventually, all the gases in air can be made to liquefy (change into a liquid).
But the reverse process also takes place. Suppose a container of liquid air holds 100 liters. The liquid air will warm up slowly. When its temperature reaches -195.79°C, liquid nitrogen changes back to a gas. Since about 78 percent of air is nitrogen, only 22 percent of the original liquid air (22 liters) will be left.
When the temperature reaches -182.96°C, oxygen changes from a liquid back to a gas. Since oxygen makes up 21 percent of air, another 21 percent (21 liters) of the liquid air will evaporate.
The work of Ramsay and Travers was very difficult, however, because the gases they were looking for are not abundant in air. Krypton, for example, makes up only about 0.000114 percent of air. For every 100 liters of liquid air, there would be only 0.00011, or about one-tenth of a milliliter of krypton. A tenth of a milliliter is about a drop. So Ramsay and Travers—although they didn't know it—were looking for one drop of krypton in 100 liters of liquid air!
Amazingly, they found it. The discovery of these three gases was a great credit to their skills as researchers. They suggested the name krypton for the new element. The name was taken from the Greek word kryptos for "hidden."
Krypton is a colorless, odorless gas. It has a boiling point of -152.9°C (-243.2°F) and a density of 3.64 grams per liter. That makes krypton about 2.8 times as dense as air.
"Look, up in the sky! It's a bird! It's a plane....
T he famous cartoon character Superman has many super powers. Everybody knows that. He's the Man of Steel. He has X-ray vision. His hearing is so good, he can tune in on one voice in a crowded city. And, of course: He's faster than a speeding bullet! More powerful than a locomotive! Able to leap tall buildings in a single bound!
But there's one substance that weakens Superman: kryptonite! If exposed to kryptonite. Superman experiences pain and loses his super powers. If exposed for too long, he can even die.
Kryptonite, of course, is purely fictional. Despite the similarity in names, kryptonite has nothing to do with element 36, krypton. According to cartoon legend, Superman came from the planet Krypton.
Kal-El, as he was originally known, was placed in a spaceship by his parents, moments before the planet exploded.
Unfortunately, as the young Superman blasted away from Krypton, a piece of kryptonite got stuck on the spaceship. The same terrible forces that caused the planet to explode, also had created the deadly kryptonite. And, as Superman would later find out, arch-villains always seem to get their hands on this green glowing rock!
Aside from the fictitious nature of kryptonite, there is another difference between it and krypton. Kryptonite is a rock—one that can cause great harm to, well, one person anyway. Krypton is an inert gas that has no effect on anything.
For many years, krypton was thought to be completely inert. Then, in the early 1960s, it was found to be possible to make certain compounds of the element. English chemist Neil Bartlett (1932-) found ways to combine noble gases with the most active element of all, fluorine. In 1963, the first krypton compounds were made—krypton difluoride (KrF 2 ) and krypton tetrafluoride (KrF 4 ). Other compounds of krypton have also been made since that time. However, these have no commercial uses. They are only laboratory curiosities.
Occurrence in nature
The abundance of krypton in the atmosphere is thought to be about 0.000108 to 0.000114 percent. The element is also formed in the Earth's crust when uranium and other radioactive elements break down. The amount in the Earth's crust is too small to estimate, however.
Six naturally occurring isotopes of krypton exist. They are krypton-78, krypton-80, krypton-82, krypton-83, krypton-84, and krypton-86. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
At least sixteen radioactive isotopes of krypton are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
One radioactive isotope of krypton is used commercially, krypton-85. It can be combined with phosphors to produce materials that shine in the dark. A phosphor is a material that shines when struck by electrons. Radiation given off by krypton-85 strikes the phosphor. The phosphor then gives off light. The same isotope is also used for detecting leaks in a container. The radioactive gas is placed inside the container to be tested. Since the gas is inert, krypton will not react with anything else in the container. But if the container has a leak, some radioactive krypton-85 will escape. The isotope can be detected with special devices for detecting radiation.
Krypton-85 is also used to study the flow of blood in the human body. It is inhaled as a gas, and then absorbed by the blood. It travels through the bloodstream and the heart along with the blood. Its pathway can be followed by a technician who holds a detection device over the patient's body. The device shows where the radioactive material is going and how fast it is moving. A doctor can determine whether this behavior is normal or not.
How long is a meter?
T he meter is the standard unit of length in the metric system. It was first defined in 1791. As part of the great changes brought by the French Revolution, an entirely new system of measurement was created: the metric system.
At first, the meter was defined in a very simple way. It was the distance between two lines scratched into a metal bar kept outside Paris. For many years, that definition was satisfactory for most purposes. Of course, it created a problem. Suppose someone in the United States was in the business of making meter sticks. That person would have to travel to Paris to make a copy of the official meter. Then the copy would have to be used to make other copies. The chances for error in this process are tremendous.
In 1960, scientists had another idea. They suggested using light produced by hot krypton as the standard of length. Here is how that standard was developed:
When an element is heated, it absorbs energy from the heat. The atoms present in the element are in an "excited," or energetic, state. Atoms normally do not remain in an excited state very long. They give off the energy they just absorbed and return to their normal, "unexcited" state.
The energy they give off can take different forms. One of those forms is light.
The kind of light given off is different for each element and for each isotope. The light usually consists of a series of very bright lines called a spectrum. The number and color of the lines produced is specific to each element and isotope.
When one isotope of krypton, krypton-86, is heated, it gives off a very clear, distinct, bright line with a reddish-orange color. Scientists decided to define the meter in terms of that line. They said that a meter is 1,650,763.73 times the width of that line.
This standard had many advantages. For one thing, almost anyone anywhere could find the official length of a meter. All one needed was the equipment to heat a sample of krypton-86. Then one had to look for the reddish-orange line produced. The length of the meter, then, was 1,650,763.73 times the width of that line.
This definition for the meter lasted only until 1983. Scientists then decided to define a meter by how fast light travels in a vacuum. This system is even more exact than the one based on krypton-86.
Krypton is still obtained by allowing liquid air to evaporate.
The only commercial uses of krypton are in various kinds of lamps. When an electric current is passed through krypton gas, it gives off a very bright light. Perhaps the most common application of this principle is in airport runway lights. These lights are so bright that they can be seen even in foggy conditions for distances up to 300 meters (1,000 feet). The lights do not burn continuously. Instead, they send out very brief pulses of light. The pulses last no more than about 10 microseconds (10 millionths of a second). They flash on and off about 40 times per minute. Krypton is also used in slide and movie projectors.
Krypton gas is also used in making "neon" lights. Neon lights are colored lights often used in advertising. They are similar to fluorescent light bulbs. But they give off a colored light because of the gas they contain. Some neon lights do contain the gas neon, but others contain other noble gases. A neon light filled with krypton, for example, glows yellow.
Compounds of krypton have been prepared in the laboratory but do not exist in nature. The synthetic (artificial) compounds are used for research purposes only.
Although neon lights sometimes do include neon, krypton is often the gas used.
There is no evidence that krypton is harmful to humans, animals, or plants.