Ar
Argon · element 18
Noble Gas · Gas at room temperature
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).
Key facts
Atomic mass
39.9481 u
how heavy one atom is
Phase (room temp.)
Gas
Density
1.784 g/L
how tightly packed it is
Melting point
83.81 K (-189 °C)
when solid turns to liquid
Boiling point
87.302 K (-186 °C)
when liquid turns to gas
Period
3
its row in the periodic table
Group
18
its column in the periodic table
Block
P-block
the neighbourhood it lives in
Electron configuration
[Ne] 3s2 3p6
where its electrons live
Shells
2 · 8 · 8
electrons in each layer, inside to out
Discovered by
Lord Rayleigh
who found it
Appearance
colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
what it looks like
Source: Wikipedia