Why does sodium have a doublet?

[dynamics]

Hi everyone i wanted to know why this is so, i know it has something to do with the quantum numbers but i want to know how and why? Your help will be greatly appreciated.

 

[jtbell]

Here's the very first hit from a Google search for "sodium doublet":

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/sodzee.html

 

[dextercioby]

It;s actually a quadruplet, as the hyperfine structure further splits each line in the 5890 and 5896 A in another 2.

 

[Gokul43201]

It;s actually a quadruplet, as the hyperfine structure further splits each line in the 5890 and 5896 A in another 2.

Why only 2? Are you neglecting the spin-splitting in the 3p states?

 

[jtbell]

A couple of clicks away from the Hyperphysics page I referenced is a really cool example of a sodium lamp!