Question

The total number of electrons in orbitals with ml = 0 for Sr? a) 2 b) 10 c) 12 d) 18 e) 34

Answer 1

I think there are 18

Explanation:

2 in 1s
2 in 2s
2 in 2p
2 in 3s
2 in 3p
2 in 4s
2 in 3d
2 in 4p
2 in 5s

Answer 2

The explanation contains some important concepts, so please read below.

Explanation:

The key lies in the fact that all the electrons in strontium are in filled subshells. This may seem surprising because strontium is highly reactive, but the reason is,one of the filled subshells (`5s`) is only loosely bound in strontium and an electronegative elemeny like chlorine can easily empty it.

Then the actual electronic structure of strontium is:

`color(blue)(1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}4s^2 4p^6)5s^2`

where the blue sushells are the unreactive core electrons corresponding to the noble gas krypton. The last two electrons, in the `5s` shell, are the valence electrons that can participate in chemical reactions. So the above structure is often shortened to:

`color(blue)(["Kr"])5s^2`

Now all you have to do is count the number of `m_l=0` orbitals in the filled subshells and allocate two electrons for each. There is one for `1s`, one for `2s`, one for `2p`, etc up to a total of nine orbitals by the time you get to the `5s` subshell valence electrons.

Thus there are (d) `18` `m_l=0` electrons.