Chemistry Reference
In-Depth Information
Models of chemical bonding
. Mental models concerning this matter have to be
viewed from two perspectives:
1. The effects of three-dimensional bonding forces are to be displayed with the
model material:
(a) Directed bonding forces that work in designated directions of space are to be
displayed by snap fasteners or sticks.
(b) Undirected bonding forces that work symmetrically around a particle are to
be symbolized by spheres, which may be glued together.
2. Bonding forces are difficult to visualize and they are usually described by
mathematical models with the distribution of electron densities. The following
cases of chemical bonding are to be differentiated:
- Ionic bonding
- Covalent bonding
- Metallic bonding
- Hydrogen bonding
- Van der Waals forces (intermolecular forces).
Models of the chemical structure
. The mathematical calculation of atomic
structure and chemical bonding is mostly a means to get information on the
chemical structure. On this basis, it is the aim of many analytical procedures to
determine and to describe the atomic or ionic arrangement in given substances, and
derive the structural formulae from the determined structures. Different cases of
chemical structures can be sketched in the following way:
- Molecular structure (atom types, bond length and bond angle)
- Atomic crystal structure (atom types and lattice constants, unit cell)
- Metal crystal structure (atom types and lattice constants, unit cell)
- Ionic crystal structure (types of ions and lattice constants, unit cell)
- Molecular crystal structure (types of molecules and lattice constants, unit cell)
Models of the chemical reaction
. Arrangements of particles in chemical reactions
can be described by mental models as well as shortened by reaction equations:
- Rearrangement of atoms in reactions of metals to alloys
- Rearrangement of ions in hydration and precipitation reactions
- Proton transfer in acid-base reactions
- Electron transfer in redox reactions
- Ligand transfer in complex reactions
- Addition, substitution and elimination reactions of organic molecules
Display models in chemistry: Chemists usually work with abstract mental
models. For educational reasons appropriate display models are being developed
(see Figs.
6.2
,
6.3
and
6.5
): concrete display models can be build, for example of
molecules or crystal structures, in regard to many mental models of different
chemical structures.
