Question

How many orbitals are completely filled in an atom whose electron configuration is 1s^2 2s^2 2p^6 3s^1?

Answer 1

Hey there!:

The 1s, 2s and 2p subshells are completely filled (a maximum of two electrons go into the 1s subshell and a maximum of two electrons go into the 2s subshell.  The 2p subshell includes 3 orbitals, with 2 electrons maximum per orbital).  The 3s subshell has only one of a maximum of two electrons.

Hope that helps!

Answer 2

The number of orbitals that are completely full is 5.

The reason you may have thought it was 3 is because you're confusing orbitals with subshells.

In this electron configuration, the sub shells are:  1s^2, 2s^2, 2p^6, 3s^1

So, we have four sub shells.

Each sub shell consists of a specific number of orbitals. s subshells have one orbital, p subshells have three orbitals, d subshells have five orbitals, and f subshells have seven orbitals. Knowing this, we can look back at the electron configuration we were given and determine how many orbitals are filled.

1s^2 has one orbital, 2s^2 has one orbital, 2p^6 has three orbitals, and 3s^1 has one orbital. The first three subshells are completely full, so a total of five orbitals are full.