The properties of elements - Geochemistry: An Introduction - page 5

Table 1.1 Electronic configuration of the light elements

Quantum numbers

Element Group n l m s Configuration

1s 1 H I 1 0 0 + 1/2

1s 2

He VIII 1 0 0 − 1/2 = [He]

[He] 2s 1 Li I 2 0 0 + 1/2

[He] 2s 2 Be II 2 0 0 − 1/2

[He] 2s 2 2p 1 B III 2 1 − 1 + 1/2

[He] 2s 2 2p 2 C IV 2 1 − 1 − 1/2

[He] 2s 2 2p 3

N V 2 1 0 + 1/2

[He] 2s 2 2p 4

− 1/2

O VI 2 1 0

[He] 2s 2 2p 5

+ +

F VII 2 1 1 1/2

[He] 2s 2 2p 6

+ − =

Ne VIII 2 1 1 1/2 [Ne]

[Ne] 3s 1

+

Na I 3 0 0 1/2

3. The third (magnetic) quantum number m (0, l ) gives the part L z of the angular

moment which points along the rotation axis; it defines the shape of the orbital.
4. The fourth quantum number s describes the momentum associated with the spin of the
electron and gives the direction of spin of the electron around its own axis relative to its
orbital movement.

± 1, ... , ±

The Pauli exclusion principle states that no two electrons can have the same quantum
numbers.
The periodic table can be constructed by assigning a unique set of quantum numbers to
each element ( Table 1.1 ) and the filling of the successive orbitals can now proceed from
lower to higher energy levels until the number of electrons matches the number of protons
in the nucleus. This holds for n , by definition, but also for l because of the electrostatic
screening by electrons on lower orbitals (see below): for example, orbital 2p is filled after
orbital 2s. The filling order is shown in Fig. 1.4 and can be exactly matched with the
periodic table.
A number of Internet sites provide detailed periodic classifications, of which I
can recommend http://www.webelements.com/ , while Dave Manthey's excellent site
http://www.orbitals.com/orb/ov.htm provides software to create very professionally drawn
orbital pictures ( Fig. 1.3 ) .
In the periodic table, groups I (alkali metals) and II (alkaline-earth metals) correspond
to the filling of s orbitals, and groups III to VIII to that of the p orbitals. The intermedi-
ate groups (transition elements such as iron and platinum) differ in the occupation of their
d orbitals. When occupied, these d orbitals are normally closer to the nucleus than the s
orbitals of the next shell out. Occupation of the orbitals is noted nx i , where x represents
the type of orbital (s, p, d, f), n its principal quantum number and i the number of electrons
it contains. Most elements of the first series (e.g. V, Cr, Mn, Fe, Co, Ni, Cu, Zn) have an
electron formula of the type [Ne]3s 2 3p 6 3d i 4s 2 , where [Ne] represents the fully occupied