Molecular models are physical models that represent molecules and the processes that occur with them. There are models based on ball and stick that reveal the complete insight of structures, bonding, and interactions of formula units or molecules. They have helped in understanding chemistry i.e. The physical properties and chemical reactivities to generate and test hypotheses.
It is because atoms and molecules are so small that they cannot be seen with the naked eye, we employ physical models to visualize the 3-Dimensional structure of molecules.
Ball and Stick Model
Ball and stick models are 3D models, with colored “balls” (spheres) representing specific atoms. The “sticks” are rods that connect the atoms and represent the chemical bonds. Two and three curved rods represent double and triple bonds respectively. These models display the relative bond lengths and bond angles, showing clearly the molecular geometry of most structures with relative ease.
An example is the representation of a carbon atom as a ball with 4 holes at tetrahedral angles (an angle of 109.5° apart) where the sticks fit into.
In addition to tetrahedral holes, there are balls with trigonal, octahedral, and 24 holes that allow rotation about the single bonds. However, the 24 holes type ball shows molecular flexibility but makes the model slack.
Furthermore, in the ball and stick model, the length (diameter) of spheres is much smaller than the length of rods so that the atoms and bonds can be seen clearly. Consequently, it fails to demonstrate the actual space occupied by the molecule.
The sticks can also be made flexible since rigid bonds and holes fail to show systems with inconsistent angles. So is the case especially with double and triple bonds which are longer and more flexible as compared to single bonds. They can restrict rotation and support geometric isomerism (cis-trans).
There are other models such as skeletal models, spherical (space-filling) models, polyhedral models, composite models, and computer-based models, in addition to the ball and stick model.
Ball and stick models can also be virtual computer models, which serve to illustrate several properties including shape, flexibility, and relative size.
This model, above all, helps in exhibiting accurate bond angles as compared to other models.
Color codes for elements
In the ball and stick model, atoms (balls) are usually represented in specific colors. These colors are conventionally used.
Comparison with Space-filling Mode
Quite often, the ball and stick model is compared to the space-filling model, which displays molecules using spheres only, to represent atoms. The advantage of this model is that the radii of spheres are made proportional to the radii of actual atoms, which gives a clearer perspective on the size of the molecule. In addition, the distance between the center of spheres is also proportional to the distance between atomic nuclei. These spheres are also given different colors to represent specific atoms.
The main difference between the two is the way chemical bonds are depicted. The space-filling model utilizes full spheres without any rods whereas the ball and stick model employs spheres as well as rods.
Moreover, bond angles, double bonds, and triple bonds can be shown using flexible rods in the ball and stick model while the space-filling model helps more clearly show the relative dimensions of the molecules.
What is the difference between structural and ball and stick models?
A structural model, like a ball and stick model, shows atoms and the bonds between them. The difference is that the ball and stick model utilizes certain colored “balls” to represent particular atoms whereas, in structural models, there are no spheres and the atoms are considered to be at the intersection of the rods (bonds) used.
What are the limitations of a ball and stick model?
- The major disadvantage of a ball and stick model is that it cannot accurately show the space occupied by a molecule considering the spheres are purposely made smaller in length as compared to the rods used. This causes the atoms to be placed farther apart in the model than they actually are (the real distance between atoms in a molecule is much shorter).
- In case of all-purpose spheres with 24 holes, the models often become floppy.
- Another limitation is that the ball and stick model fails to show the movement of electrons in ionic compounds.
What are the types of molecular models?
The types of molecular models are skeletal models, spherical models, space-filling models, crystal-lattice models, polyhedral models, composite models, and computer-based models.
Why isn’t the ball and stick model a true representation?
Mostly because a true representation should have accurate relative dimensions of the molecules; the space they occupy and the distance between the atoms. This is where the ball and stick model falls short, as the bond lengths are made longer compared to the radii of the atoms (the real distance between atoms is much shorter).
Why is the ball and stick model accurate?
The ball and stick model’s accuracy lies in correctly representing the bond angles. Being an “open” model, unlike the space-filling model, the atoms and bonds can be seen clearly to understand the geometry of a molecule.
What are the four types of bonding?
The four main types of bonds are ionic bond, covalent bond, co-ordinate/dative covalent bond, and metallic bond.
What do the sticks represent in a ball and stick model?
In a ball and stick model, the sticks (rods) represent the bonds between atoms in a molecule. Furthermore, two and three more flexible and longer (curved) sticks are used to represent the double and triple bonds respectively.
Why are bonds more like springs than sticks?
Bonds can stretch, bend and rotate without breaking. They can be assumed to be more like flexible springs than rigid sticks. This is also the principle for infrared (IR) spectroscopy, which works on vibrational level changes in a molecule.
There are vibrational modes that include stretching, bending, scissoring, rocking, twisting, and wagging.
What are the two limitations of a 3D model?
One limitation of a 3D model is that all geometrical details cannot be included in a single model i.e. The ball and stick model can accurately represent the bond angles but it fails to show the relative space occupied by the molecule. On the other hand, the space-filling model focuses on the dimensions of a molecule but cannot show the bonds, or the angles between them.
Another limitation is that the models can be made to show more accurate information but this comes at the cost of simplicity i.e. the model becomes complex. Simpler models, such as the ball and stick model, are preferred because these can help in easily visualizing the geometry of molecules.
What are the advantages of a space-filling model?
A space-filling model can show, quite accurately, the relative space an atom or a molecule occupies. The model is simple as well. It can also show the overlapping of molecular orbitals in the molecules.
Space-filling model vs ball and stick model.
The notable difference between the two is the way chemical bonds are shown. The ball and stick model uses rods as “sticks” to show the bonds while the space-filling model works with Van der Waals spheres only and the bonds are not shown.
Being an “open” system, the ball and stick model can show the geometry of the molecule more clearly. On the contrary, the space-filling model, a “closed” system, can show the relative size of the molecule better.
How is a methane ball and stick model made?
In a methane ball and stick model, the central carbon atom is represented by a sphere with tetrahedral holes, which corresponds to the geometry of the molecule. Four rods attached to hydrogen atom spheres fit into these tetrahedral holes. The rods are 109.5° apart. The bonds and atoms can thus be seen clearly.
Do molecules actually look like the ball and stick models we represent them with?
While the ball and stick model can clearly display the geometry of a molecule, it is unable to show the relative sizes of the atoms and the bonds in a molecule.
Why are ball and stick models useful in organic chemistry?
The ball and stick models can help in visualizing and understanding the geometry of large and complex organic molecules that are otherwise hard to imagine. Among other things, the delocalization of electrons requires a certain arrangement of atoms in the molecule, which influences several other factors that determine the progress and mechanism of a reaction.
What does the ball and stick model of NaCl look like?
In the ball and stick model of sodium chloride, NaCl, each Na+ ion is surrounded by 6 Cl– ions and vice versa. This arrangement is known as the ionic lattice of NaCl, which is face-centered cubic (fcc).
The oppositely charged ions are held together by the electrostatic forces of attraction between them (ionic bonds). The ratio of Na+ to Cl– ions remains 1:1 in the lattice and so the formula of the compound is NaCl.