Chemistry Reference
In-Depth Information
5. Substances can be distinguished by the kind of atoms and by their spatial
arrangement
Since Arrhenius postulated in 1884 that ions are the other big group of funda-
mental particles of matter, Dalton's statements have to be applied to ions as well. It
can be claimed that all matter of the universe is built of atoms or ions. Two
substances are identical, when they correspond in the kind of atoms or ions and
in their spatial arrangement, in their chemical structure.
Accordingly today's chemists have to:
- Detect the kind of atoms or ions bound in a substance.
- Analyze the spatial arrangement of the atoms or ions with different methods of
instrumental analysis.
On the other hand, one has to know, which kind of atoms or ions have to be
visualized and how they are connected spatially for a substance to have mental
models or to build concrete models of the structure. When the model of a sodium
crystal is being built mentally, Na atoms have to be connected in a way that they
form a cubic body-centered lattice. When the model for a sodium chloride crystal is
being built, spheres as models for Na
+
ions and bigger spheres as models for Cl
ions have to be connected to a cubic face-centered structure.
In reality, fundamental particles can only be connected when they show the same
quality of bonding forces. Experiments and laboratory experiences from the last
centuries led to three classes of basic particles with different types of attractive
forces:
1. Metal atoms
2. Nonmetal atoms
3. Ions
Metal atoms with the same type of attractive forces are placed on the left side of
the PSE and nonmetal atoms with another type of attraction are placed on the right
side (see Fig.
10.4
) - therefore, the H atom and H
ion is placed on the right side of
PSE close to the 7th group. Ions with the third kind of attractive forces are placed on
both sides; cations on the left side together with their metal atoms, anions on the
right side together with their kind of nonmetal atoms. Special rules of combination
show that atoms with the same type of attractive forces can be combined
(see Table
10.1
).
Nondirectional bonding forces are forces, which a particle reveals spherically
symmetrical in all directions of space: such particles form crystal lattices. Any
number of metal atoms, for example, can be connected in a metal structure.
Table 10.1 Rules of combination for atoms and ions as fundamental particles of matter [
7
]
Position in PSE
Kind of articles
Bonding
Structure
“Left and left”
Metal atoms
Spatially undirected
Metal structure
“Left and right”
Ions
Spatially undirected
Ionic structure
“Right and right”
Nonmetal atoms
Spatially directed
Molecule or atomic lattice
