Chemistry, Third edition

3 · INSIDE THE ATOM

Orbitals and sublevels

We now return to the order in which the sublevels of electrons in atoms are filled,

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10...

where the superscripts show the maximum number of electrons in each sublevel.

Electrons in a 1s orbital occupy the 1s energy sublevel, electrons in a 2s orbital

occupy the 2s sublevel and electrons in a 3s orbital occupy the 3s sublevel.

Electrons in any of the three p orbitals are normally equal in energy and occupy the

2p sublevel. There are five d orbitals: electrons in these orbitals will occupy the 3d

sublevel.

The use of ‘boxes’ may help make this clearer. In the aluminium atom (electronic

configuration 1s^2 2s^2 2p^6 3s^2 3p^1 ) the 13 electrons occupy the following orbitals:

Electrons in orbitals: ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑

px py pz py, pxor pz

1442443

Type of orbitals: 1s 2s 2p 3s 3p

where the 3p^1 electron occupies either the 3py, 3pxor 3pzorbital, all of which are of

equal energy.

The 1s, 2s, 2p and 3s orbitals in the phosphorus atom (1s^2 2s^2 2p^6 3s^2 3p^3 ) are

filled in the same way as for aluminium, with the complication that it is unclear

whether the 3p electrons feed into two of the 3p orbitals:

↑↓ ↑

3px 3py

or whether they enter all three p orbitals:

↑ ↑ ↑

3px 3py 3pz

Fig. 3.13The shape of an s
orbital and of the three types
of p orbitals.

44

px py pz

(ii) The three p orbitals

(i) s orbital

z z z

y xy xy x