Molecular model

A molecular model is a physical representation of an atomistic system. These models represent molecules and the processes they undergo. They are vital tools for understanding the complexities of chemistry. Scientists use them to generate and test new scientific hypotheses. Molecular modeling refers to the creation of mathematical models for molecular behavior. When these models are shown visually, it is called molecular graphics. Most molecular models contain one or more explicit atoms. They often neglect the nuclear structure of these atoms. The electronic structure is also frequently omitted unless it helps explain a specific function.

There are several distinct reasons why scientists create these models. They serve as pedagogic tools for students learning about atomistic structures. They also act as objects to test theories, such as the structure of DNA. Some models function as analogue computers to measure distances and angles in flexible systems. Beyond science, they can be aesthetically pleasing objects that sit between art and science. The construction of these physical models is often a creative and bespoke process. Many are carefully crafted in the workshops of science departments.

Physical modeling follows many different approaches. The ball-and-stick model is a very popular method. In this system, balls represent atoms and sticks represent chemical bonds. Early versions used wooden balls with drilled holes for rods. Carbon can be shown as a sphere with four holes at tetrahedral angles. To allow for different angles, scientists use flexible bonds. These were once helical springs but are now usually made of plastic. This flexibility allows models to approximate double and triple bonds.

Another major type is the sphere-based or space-filling model. These models represent atoms as spheres to show how they pack together. This is very useful for studying crystallography and solid-state inorganic structures. For example, sodium chloride (NaCl) can be described as close-packed chloride ions. These ions form a face-centered cubic lattice. The sodium ions then sit in the octahedral holes. This method helps visualize how different sized spheres create specific cubic structures.

Skeletal models provide a different way to view molecular connections. In these models, atoms are represented simply as points at the intersections of rods. The valences are represented by rods or tubular connectors. André Dreiding introduced a kit in the late 1950s that used valence spikes. These spikes click into tubes to form a bond. This method is widely used in organic chemistry departments. Some modern versions use inexpensive plastic with protuberances. The flexibility of the plastic allows for the creation of distorted geometries.

The history of molecular modeling spans several centuries. In the 1600s, Johannes Kepler speculated on the symmetry of snowflakes. He studied how spherical objects like fruit could pack together. In 1860, August Wilhelm von Hofmann is credited with the first physical molecular model.

However, his methane model depicted an incorrect geometry. It did not yet account for the importance of stereochemistry. Later, Jacobus Henricus van 't Hoff and Joseph Le Bel introduced three-dimensional chemistry. Van 't Hoff built tetrahedral models to represent carbon properties. This helped establish the field of stereochemistry.

Modern technology has introduced highly advanced modeling methods. Scientists can now use rapid prototyping to make complete single-piece models. These are often made of plaster or starch. Some companies use subsurface laser engraving to etch proteins inside glass blocks.

Computers also use mathematical programs to predict molecular properties. These programs can calculate bond lengths, polarity, and charge distribution. However, as more atoms are added, the number of calculations grows quadratically. This means a molecule with four times the atoms takes 16 times longer to calculate. For very complex tasks like drug design, scientists often require supercomputers or quantum computers.