Chemistry Reference
In-Depth Information
Fig. 6.5 Space-filling,
ball
-and-
stick
and
stick
model of the structure of the C
2
H
5
OH molecule
Models of molecule structures
. The spatial arrangement of atoms in a molecule is
described with the help of space coordinates, bond lengths and bond angles, which
are to be determined experimentally in the laboratory. It can be illustrated in
different ways (see Fig.
6.5
):
- Space-filling model (calotte model): the space filling of atoms is being displayed,
atom calottes are connected to a molecular model, according to bond lengths and
bond angles (a).
- Ball-and-stick model: all balls for the different kinds of atoms have the same
size and are specially colored, they are being connected with connection sticks
or snap fasteners (b).
- Stick model: instead of balls special sticks are used of appropriate lengths and
connected with proper angles (c).
Models of crystal structures
. The unit cell is sufficient for the expert to deduce
the whole structure. To proceed graphically for the learner, certain parts of the
lattice are being chosen to be displayed in models as a crystal structure or a packing
of spheres (see Fig.
6.3
):
- Crystal structure model: equal spheres, with different colors if applicable, are
being connected by connection sticks until the desired part of the structure is
being displayed, for example, the part corresponding to the NaCl unit cell (a).
- Packing-of-spheres model: the size ratio of the different atoms or ions is taken
into account. The balls are to be glued or piled up according to familiar structure
parameters until they display the desired part e.g. the NaCl unit cube (b).
- Unit cell model: it is derived from the corresponding unit cube model and
guarantees a proper ratio of atoms or ions (c). Larger structures of any size can
be derived by mental translation of unit cell models in all three directions in
space.
- 3D-drawing model: red-green drawings of chemical structures are being fixed
by both eyes until the three-dimensional picture appears; it can be interpreted
spatially [
5
].
Besides the well-known molecular structure kits there exist a variety of model
kits to build packings of spheres:
