They can be forced to form compounds with other elements, but require special conditions to do so. Helium is a colorless, odorless, unreactive gas which liquefies at The name "helium" is derived from the Greek word for the Sun, helios. Helium was originally discovered on the Sun in by Pierre Janssen: his analysis of the light emitted from the Sun's corona during a solar eclipse showed that there were lines in the Sun's spectrum that were produced by a previously unknown element.
When helium was found on Earth in the late 's in association with uranium ores , it was found to have the same emission spectrum as the element previously found in the Sun, indicating that it was indeed the same element. The concentration of helium in the Earth's crust is about 8 ppb, making it the 71st most abundant element; it is found in the atmosphere at a concentration of 5 ppm by volume.
It is found in some minerals, where it is produced by radioactive elements that decay by alpha particle emission see below. Of course, there's also "dark matter" and "dark energy" to worry about, but that's another story. Hydrogen, helium, and trace amounts of lithium were produced at the beginning of the Universe in the Big Bang, and became concentrated into stars by the force of gravity. The fusion of hydrogen atoms in stars to produce helium produces huge amounts of energy; the energy in sunlight is captured by plants in photosynthesis, and drives most of the chemistry of living organisms.
The most common isotope of helium, helium-4, consists of two protons and two neutrons in the nucleus, surrounded by two electrons. Helium is found along with some radioactive minerals that decay by alpha particle emission, however the concentration of helium in these minerals is very low.
The main source of helium is from natural gas, where it is separated out from the other components by fractional distillation. Helium liquefies at 4. Some materials become superconductors when immersed in liquid helium; in these materials, there is no resistance to the flow of electricity.
Superconducting magnets are used for an important medical imaging technology called Magnetic Resonance Imaging MRI , which allows images of tissues and organs to be obtained.
A related technology is used by chemists to obtain information that can be used to deduce the structures of molecules; this technique is called Nuclear Magnetic Resonance NMR ; the two technologies are basically the same, but the term "nuclear" is avoided in the medical application because of its unpleasant associations even though there is no nuclear radiation involved.
The elements in group 0 are called the noble gases. They belong to the right-hand column in the periodic table. The noble gases are all chemically unreactive which means they are inert.
Halogens display physical and chemical properties typical of nonmetals. They have relatively low melting and boiling points that increase steadily down the group. Near room temperature, the halogens span all of the physical states: Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Halogens are highly reactive , and they can be harmful or lethal to biological organisms in sufficient quantities.
This reactivity is due to high electronegativity and high effective nuclear charge. Halogens can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements. Davy's name for the element prevailed.
Noble gas. The noble gases are the chemical elements in group 18 of the periodic table. They are the most stable due to having the maximum number of valence electrons their outer shell can hold. Therefore, they rarely react with other elements since they are already stable. The noble gases are in Group 18 8A. They are helium, neon, argon, krypton, xenon, and radon. They were once called inert gases because they were thought to be completely inert —unable to form compounds.
Because this configuration is extremely stable as well as symmetrical, the noble gases are very unreactive. The periodic table also has a special name for its vertical columns.
It also explains why atoms of group 0 elements do not share electrons to form molecules. Group 0 - chemical properties Compared to other elements , the noble gases are inert - they are extremely unreactive and do not take part in chemical reactions. This is stated as the octet "group of eight" rule. According to this rule, atoms react to form compounds that allow them to have a group of eight valence electrons like the noble gases. For example, sodium with one valence electron reacts with chlorine with seven valence electrons to form the stable compound sodium chloride table salt.
In this reaction, sodium donates an electron and chlorine accepts it, giving each element an octet of valence electrons. Have you ever had helium balloons like those in the elephant image? Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so that it won't float away—although you don't have to use an elephant!
Early incandescent light bulbs, like the one pictured in the figure below, didn't last very long. The filaments quickly burned out. Although air was pumped out of the bulb, it wasn't a complete vacuum. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass.
Filling a light bulb with argon gas prevents these problems.
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