Argon, Ar 
Index
Argon is an inert gas in group VIII A of the periodic table with atomic number 18, an atomic weight of 39.948, and a density of 1.40 Mg/m3. In the solid state it forms an fcc crystal with a melting point of -189.4 C and a boiling point of - 185.8 C.

The electronic configuration of Argon is (Ne)(3s2)(3p6). Its atomic radius is 0.098 nm.
 

From: Callister, "Materials Science and Engineering," Wiley (1997)