Chemistry, Third edition

Figure 3.10 shows the arrangement of electrons in shells (the so-called elec-

tronic structureorelectronic configuration) for atoms of elements with atomic

numbers from 1 to 10 in their lowest energy levels. Also shown is the shorthand for

such electronic structures; for example, 2.6 (read as ‘two dot six’) means that there

are two electrons in the first shell (for which n1) and six electrons in the second

shell (for which n2). The configurations of atoms containing the same shells of

electrons as in helium, neon (or other ‘noble gases’ such as argon) are sometimes

abbreviated, as in the following examples:

Li 2.1 becomes [He].1

Mg 2.8.2 becomes [Ne].2

Cl 2.8.7 becomes [Ne].7

Table 3.3 gives electronic structures for elements with atomic numbers 1–20.

ELECTRONIC STRUCTURE OF ATOMS 39

Table 3.3The electronic structure for elements with atomic

numbers 1–20. The last column will be filled in later on in this unit

Element and symbol Atomic number Bohr structure s,p,d,f structure

Hydrogen H 1 1.
Helium He 2 2. or [He]
Lithium Li 3 2.1 or [He].1
Beryllium Be 4 2.2 or [He].2
Boron B 5 2.3 or [He].3
Carbon C 6 2.4 or [He].4
Nitrogen N 7 2.5 or [He].5
Oxygen O 8 2.6 or [He].6
Fluorine F 9 2.7 or [He].7
Neon Ne 10 2.8 or [Ne]
Sodium Na 11 2.8.1 or [Ne].1
Magnesium Mg 12 2.8.2 or [Ne].2
Aluminium Al 13 2.8.3 or [Ne].3
Silicon Si 14 2.8.4 or [Ne].4
Phosphorus P 15 2.8.5 or [Ne].5
Sulfur S 16 2.8.6 or [Ne].6
Chlorine Cl 17 2.8.7 or [Ne].7
Argon Ar 18 2.8.8 or [Ar]
Potassium K 19 2.8.8.1 or [Ar].1
Calcium Ca 20 2.8.8.2 or [Ar].2

Fig. 3.10The electronic structure of atoms for

elements with atomic numbers 1–10.