Chemistry Reference
In-Depth Information
(see Fig. 10.4, see also colored Periodic table in www.thinking-chemistry.org). Ions
that were left out for reasons of clarity can be added if needed (for example Cu
2+
,
Pb
2+
). Salt structures can be developed by combination of the ions on the left and
right side of the periodic table; they can also be built as concrete models like sphere
packing (see Chaps. 6 and 10). Chemical symbols for salt crystals can be derived
from the charge number of the ions: this way the students theoretically combine
Al
3+
ions and O
2
ions to an ion lattice with an ion ratio of 2:3, they may find
familiar symbols like {(Al
3+
)
2
(O
2
)
3
}orAl
2
O
3
(Table
7.4
).
In general it is possible to combine atoms and ions systematically with a few
specific guidelines:
- Metal atoms “left and left in PSE” can be combined with undirected bonding to
giant structures: models of metal and alloy crystals, visualized by packing of
spheres (see Chap. 6).
- Nonmetal atoms “right and right in PSE” bond with directed bonding with
particular bonding numbers, resulting in molecules or atomic structures (see
Chap. 6).
- Ions “left and right in PSE” bond undirected to giant structures of ions with
specific charge numbers, so called ionic structures visualized by special sphere
packing (see Chap. 6).
On the basis of Dalton's model chemical reactions can only be described in those
cases where the nature of particles does not change. Metal-metal reactions to
alloys, nonmetal-nonmetal reactions to volatile substances, or reactions between
salt solutions with precipitation: for example the precipitation of insoluble green
iron hydroxide from corresponding salt solutions (see Fig.
7.8
). In these cases the
quality of particles does not change during the reaction: atoms remain atoms, ions
Table 7.4 Rules for combining metal atoms, nonmetal atoms and ions (see Fig.
7.7
)
Chemical
structure
Places in the periodic table
Particle quality
Bonding type
Left + left in PSE
Metal atoms
Spatially undirected
Metal lattice
Right + right in PSE
Nonmetal atoms
Spatially directed
Molecule
Left + right in PSE
Ions
Spatially undirected
Ionic lattice
Fig. 7.8 Models and symbols of the precipitation of iron hydroxide from salt solutions
