The key difference between molecular formula and structural formula is that molecular formula gives the chemical elements present in a compound and their numbers, whereas structural formula gives the drawing of the structure of the molecule.
The terms molecular formula and structural formula are closely related terms that are often confused with each other. However, they are two different terms.
CONTENTS
1. Overview and Key Difference
2. What is Molecular Formula
3. What is Structural Formula
4. Molecular Formula vs Structural Formula in Tabular Form
5. Summary – Molecular Formula vs Structural Formula
What is Molecular Formula?
Molecular formula is a formula showing the type of atoms and the number of each atom connected in the molecule. Typically, the atoms are depicted by their symbols, which are shown in the periodic table. Moreover, we should write the numbers of atoms as subscripts. Some molecular formulas are neutral (no charge), but if there is a charge, we can show it on the right side of it as a superscript.
Figure 01: Molecular Formula
Generally, we can use the molecular formula in chemical reactions or when documenting any chemical details. By just looking at the molecular formula, we can get a lot of information about the molecule. For example, we can calculate the molecular mass. Moreover, if it is an ionic compound, we can predict what the ions are and how many of them will be released when it is dissolved in water.
Furthermore, we can predict the oxidation numbers of each atom, how they are going to react in a reaction, and the resultant products using molecular formulas. However, we cannot predict the exact molecular arrangement only from the molecular formula. This is because sometimes, there are several structural formulas for a single molecular formula. These are “isomers.” Isomers have the same molecular formula but can differ from the connectivity of atoms (constitutional isomers) or the spatial arrangement of atoms (stereoisomers). Therefore, by looking at the molecular formula, we can write all the possible isomers for a molecule.
What is Structural Formula?
Structural formula of a chemical compound is an important way of showing the types of atoms present in a particular compound and the connectivity of these atoms. In other words, the structural formula shows us how the atoms are bonded to each other and the type of bonds in the molecule (e.g. single bonds, double bonds, and triple bonds).
Figure 02: Structural Formulas of Different Chemical Compounds
Generally, a structural formula gives the location of chemical bonds between the atoms using small, short lines that represent the chemical bond. These lines are only used to show covalent bonds. We can show ionic bonds in the structural formula. But sometimes, plus and minus signs (+ and -) are used to show the ions in an ionic compound. When using short lines, single lines show single covalent bonds, two parallel lines show double bonds, and three parallel lines show triple covalent bonds.
The atoms are written using the chemical symbol as given in the periodic table. The short line that represents the chemical bond is drawn between two atoms. Sometimes, to avoid complexities, the group of atoms is attached through short lines, e.g. functional groups can be written as a group of atoms.
What is the Difference Between Molecular Formula and Structural Formula?
A molecular formula is important as the first glance at a chemical compound, but a structural formula is important because it shows the arrangement of the molecule as well. The key difference between molecular formula and the structural formula is that a molecular formula gives the chemical elements present in a compound and their numbers, whereas a structural formula gives the drawing of the structure of the molecule.
Summary – Molecular Formula vs Structural Formula
There are many important uses of molecular formulas and structural formulas, including the determination of the properties of the compounds. The key difference between molecular formula and the structural formula is that molecular formula gives the chemical elements present in a compound and their numbers, whereas structural formula gives the drawing of the structure of the molecule.
Reference:
1. “Structural Formula.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
Image Courtesy:
1. “Naming-and-Writing-Formulas-of-Covalent-Compounds” By Zappys Technology Solutions (CC BY 2.0) via Flickr
2. “The structure formulas of different types of pheromones” By Encyclopedia2 – The Free Dictionary (CC BY-SA 4.0) via Commons Wikimedia