The key difference between molecules and compounds is that molecules form by the combination of the same or different elements while compounds form by the combination of different types of chemical elements.
Atoms are the tiny units that form all chemical substances. Moreover, atoms can join with other atoms in various ways and form thousands of molecules. All elements except Nobel gases have a diatomic or polyatomic arrangement to become stable. Furthermore, according to their electron-donating or withdrawing abilities, they can form covalent bonds or ionic bonds. Sometimes, there are very weak attractions between atoms. Molecules and compounds are two words to distinguish between these large numbers of chemical substances. They can be present in a solid, gaseous or liquid phase.
CONTENTS
1. Overview and Key Difference
2. What are Molecules
3. What are Compounds
4. Side by Side Comparison – Molecules vs Compounds in Tabular Form
5. Summary
What are Molecules?
Molecules are made up by chemically bonding two or more atoms of the same element (e.g: O2, N2) or different elements (H2O, NH3). Molecules don’t have a charge, and the atoms bind via covalent bonds. Moreover, molecules are either very large (hemoglobin) or very small (H2), depending on the number of atoms that connect with each other to form the molecule.
The molecular formula gives the type and number of atoms in a molecule. Moreover, the empirical formula gives the simplest integer ratio of atoms present in a molecule. For example, C6H12O6 is the molecular formula of glucose, while CH2O is the empirical formula.
Figure 01: Ozone is a Homonucelar Molecule
Furthermore, the molecular mass is the mass calculated considering the total number of atoms given in the molecular formula. Each molecule has its own geometry. In addition, the atoms in a molecule are arranged in the most stable manner, with specific bond angle and bond lengths to minimize the repulsions and straining forces.
What are Compounds?
Compounds are chemical substances containing two or more different chemical elements. Combinations of two or more of the same chemical elements are not compounds. For example, diatomic molecules like O2, H2, N2 or polyatomic molecules like P4 are not compounds; we consider them as molecules. NaCl, H2O, HNO3, C6H12O6 are some examples of common compounds. Therefore, compounds are a subset of molecules.
Figure 02: Compounds Contain Different Atoms of Different Chemical Elements
Moreover, the elements in a compound join together via covalent bonds, ionic bonds, metallic bonds, etc. The structure of the compound gives the number of atoms in the compound and their ratios. In a compound, elements are present in a definite proportion. We can find these details easily by looking at a chemical formula of a compound. Furthermore, compounds are stable and they have a characteristic shape, colour, properties, etc.
What is the Difference Between Molecules and Compounds?
The key difference between molecules and compounds is that molecules are formed by the combination of the same or different elements while compounds are formed by the combination of different types of chemical elements. Furthermore, in molecules, atoms bind mainly via covalent bonds while in compounds, the atoms can bind via covalent, ionic or metallic bonds. Moreover, molecules can be either homonuclear of heteronuclear while compounds are heteronuclear.
Summary – Molecules vs Compounds
Compounds are a subset of molecules. The key difference between molecules and compounds is that molecules form by the combination of the same or different elements, but compounds form only by the combination of different types of chemical elements. Therefore, all the compounds are molecules but all molecules are not compounds.
Reference:
1. Helmenstine, Anne Marie. “What Is a Molecule?” ThoughtCo, Jul. 9, 2019, Available here.
Image Courtesy:
1. “Ozone-CRC-MW-3D-vdW” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
2. “855588” (CC0) via Pixabay