Molecular Structure

Bookmark added to your notes.
View Notes
×

What are Molecular Structure and Bonding?

As the title indicates, the molecular structure is the three-dimensional shape or configuration of a molecule. There are several different characteristics that one learns about by looking at the molecular structure definition of a molecule or group of atoms.

It should be noted that the shape of a molecule is also dependent on the preferred spatial orientation of covalent bonds between two atoms that have two or more bonding partners. There are also different dimensional configurations that one can view with the help of a model. These configurations can be represented on paper by using perspective drawing.

In perspective drawing, the direction of the bond is specified by a line that connects both the bonded atoms. There are several types of lines that signify different bonds. Some of those bonds, their lines, and representations are given below.




It is also vital to note here that usually, the focus of a configuration is the carbon atom. This means that the lines specifying the bond directions will all originate from the carbon atom. For example, a straight line from the carbon atom indicates that the bond is approximately lying on the surface plane.

Students should also remember that some textbooks and other sources use a dashed bond in a similar manner to the hatched bond that has been used in this article. If a student ever comes across it, then he or she should not be confused. This is especially true for covalent bonds because those bonds are either partially formed or partially broken.

It is also extremely important for students to show non-bonding valence shell electron pairs in their molecular structures. Missing these electron pairs can create a lot of confusion. For example, the structure of methane, ammonia, and water is almost similar. But the main difference exists in terms of the valence shell electron pairs. This example is also illustrated in the image that is attached below.

                                  


It is also possible to predict the bonding configurations. This can be done by using the valence-shell electron-pair repulsion theory. This theory is also referred to as the VSEPR theory and it is present in most introductory chemistry courses.

This model is quite simple as it is based on the fact that electrons naturally repel one another. Further, it is also reasonable to expect that the non-bonding valence electron pairs and bonds associated with any given atom will prefer to be as far apart from one another as possible.

At this point, students should remember the bonding configurations of carbon. These configurations are easy to remember and can be classified into three categories. These categories are shown in the table that is given below.


Configuration

Bonding Partners

Bond Angles

Example

Tetrahedral

4

109.5°


































































Trigonal

3

120°

Linear

2

180°


It can also be fun to learn the molecular structure of glucose, the molecular structure of water, and know the difference between molecular structure vs chemical structure.


What are Isomers?

There are compounds that have the same molecular formula but a different structure. These compounds are known as isomers. This is one of the reasons why it is necessary for students to draw the structural formulas for organic compounds.

It should also be noted that the presence of organic isomers reflects the amazing versatility of carbon in forming strong bonds with itself and with other elements. Also, constitutional isomers are compounds that are bonded with each other in fundamentally different ways. These compounds are the group of atoms that make up the molecules of various isomers.

For example, as of now, there are seven constitutional isomers of C4H10O. The structural formulas for these isomers are also different. It should be noted that there are no double bonds, triple bonds, or rings in any of these structures. Further, each of the carbon atoms is bonded to four other atoms and is saturated with bonding partners.


Fun Facts About the Distinguishing Between Carbon Atoms

Did you know that you can distinguish between different groups of carbon atoms by their structural characteristics? For example, you can find a primary carbon by identifying the one that is bonded to no more than a single carbon atom.

A secondary carbon is the kind of carbon that is bonded to two other carbon atoms. Similarly, a tertiary carbon is bonded to three carbons and a quaternary carbon is bonded to four other carbons. You can also find the three isomers of C5H12 illustrated below.

                            

It is also possible for several structural differences to occur within these four groups of carbons. This depends on the molecular constitution. One can also take the consideration of molecular symmetry into account to help distinguish between structurally equivalent and nonequivalent groups and atoms. Also, it is a part of mastering organic chemistry to learn how to distinguish the structural differences and how to draw molecular structure. One can learn this skill through experience and practice.

FAQ (Frequently Asked Questions)

Question 1. What are the Favorable Factors that are Required for the Formation of Ionic Bonds?

Answer: The favorable factors required for the formation of ionic bonds are:

  • Low ionization enthalpy of metal atoms.

  • High lattice enthalpy of the compounds that are formed.

  • High electron gain enthalpy of non-metal atoms.

Question 2. We Know that the Geometries of NH3 and H2O Molecules have Distorted Tetrahedral but the Bond Angle in Water is Still Less Than that of Ammonia. Why?

Answer:

NH3 → N̈H3

H2O → HÖ:


In this equation, one can see two lone pairs of electrons on the O atom. This means that the repulsion on bond pairs is larger in H2O in comparison to NH3. Hence, the bond angle is less in H2O molecules.

Question 3. How can Bond Strength be Expressed in Terms of the Bond Order?

Answer: Bond strength is directly proportional to the bond order. This means that the greater the bond order, the more is the bond strength.

Question 4. What is the Meaning of Bond-Length?

Answer: Bond-length can be defined as the equilibrium distance that exists between the nuclei of two bonded atoms that are present in a molecule. Bond-lengths are usually measured by spectroscopic methods.