Electron configuration

Question

What is the ground-state electron configuration of an oxygen atom?

-[He]2s³2p³

-[He]2s²2p⁴

-[Ne]2s²2p⁴

-[He]2p⁶

-[Ne]2p⁶

Answer 1

For O,

 

Z = 8.

 

Its ground state electronic configuration must be

 

1s²2s²2p⁴

 

[He] is 1s²

 

Then the electronic configuration of O is

 

[He]2s²2p⁴

 

You can also get this by starting with the electronic configuration of the nearest noble gas that precedes O in the periodic table, and adding electrons until you are at the Z for O, filling in orbitals according to the aufbau order.