The chemical element argon has the atomic number 18 and the symbol Ar. It is a noble gas belonging to group 18 of the periodic table. [With a concentration of 0,934, argon is the third most abundant gas on Earth (9340 ppmv). It is 400 times more than carbon dioxide (23 ppmv), 500 times more than neon, and twice as much as water vapor (4000 ppmv), which averages around 18 ppmv but varies significantly. Argon, the most common noble gas in the earth's crust, makes up 0,00015% of the earth's crust.
Most of the argon in the planet's atmosphere is radiogenic argon-40, which is released when potassium-40 in the planet's crust decays. Argon-36 is the most common argon isotope in the universe because it can be easily produced by stellar nucleosynthesis in supernovae.
The word “argon” is derived from the Greek word “v” meaning “lazy” or “inactive” and refers to the fact that the element hardly ever undergoes a chemical reaction. The outer atomic shell of argon contains a full octet of eight electrons, which makes it stable and prevents it from bonding with other elements. The triple point temperature, 83.8058 K, is a defining fixed point on the 1990 International Temperature Scale.
Industrial fractional distillation of liquid air produces argon. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon is primarily used as an inert shielding gas in welding and other high temperature industrial processes where typically non-reactive materials become reactive. Incandescent, fluorescent and other lighting fixtures along with other gas discharge tubes use argon. The characteristic blue-green gas is produced by laser argon. Additionally, fluorescent glow starters use argon.
Argon is 2,5 times more soluble in water than nitrogen and roughly as soluble as oxygen. As a solid, liquid, or gas, argon has no color or odor, is flammable, and is non-toxic. Most of the time, argon is chemically inert and does not form any known stable compounds at ambient temperature.
Despite being a noble gas, argon can still form certain compounds in some extreme cases. Argon fluorohydride (HArF), a combination of argon with fluorine and hydrogen, has proven to be stable below 17 K (256,1 °C; 429,1 °F). While the neutral ground state chemical compounds of argon are currently limited to HArF, argon atoms can form clathrates with water when encased in a lattice of water molecules.
It has been proven that ions such as ArH+ and excited state complexes such as ArF exist. Numerous other argon compounds that have not yet been produced but must be stable are predicted by theoretical calculations.
Günceleme: 30/01/2023 20:22
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