Argon (Ar), element 18 – Learn Acer periodic table

Argon

Noble gas, atomic number 18.

Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most common gas in the Earth's atmosphere, at 0.934% (9,340 ppmv), making it over twice as abundant as the next most common atmospheric gas, water vapor (which averages about 4000 ppmv, but varies greatly), and 23 times as abundant as the next most common non-condensing atmospheric gas, carbon dioxide (400 ppmv), and more than 500 times as abundant as the next most common noble gas, neon (18 ppmv).

Facts

Symbol Ar. Atomic mass 39.9481 u. Group 18, period 3. Electron configuration [Ne] 3s2 3p6. Electrons per shell 2, 8, 8. State at room temperature: Gas. Melting point -189.3 °C, boiling point -185.8 °C. Discovered by Lord Rayleigh.

Element data from Wikipedia, CC BY-SA 3.0.