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Difference between Molecules and Compound

Molecules and compound

Molecules and compounds are two very basic terminologies that teachers add in the science books of as low as Grade 6 and 7. When two or more same atoms combine through a chemical bond, they form a molecule. On the other hand, a compound is formed by combining two or more atoms that can be of different elements. Hence, we can say that all compounds can be called molecules, but not all are compounds. Molecules and compounds can only be seen under an electron microscope unlike compound microscope.

Besides, there are many more differences between the two that we have planned to discuss in this article today. So, let’s begin with a quick comparison table before heading toward their detailed differences.

Comparison Table

InterrelationNot all molecules
are compounds
All compounds
are molecules
Bonding TypesIonic & CovalentIonic, Covalent
& Metallic
of Substance
Homo or
hetero nuclear
Heteronuclear only
VisibilityThrough microscopeWith naked eye
ExampleWater, Cl2,
& ozone
Fructose, gasoline,
& ammonia

Explanation of a Molecule


A molecule is a group of atoms bonded together by a chemical bond that are the smallest fundamental units and consist of all the properties. The chemical reaction of atoms forms molecules. These atoms are held together by shared electron pairs or covalent bonds. A molecule is weighed in gram molecular mass, also called a mole.

Mole: It is the sum of the atomic weights of all its component atoms

Furthermore, the SI unit of molecular mass is kilogram per mole & the formula tends to be:

M = m/n

m = mass of a substance (in grams)

n = number of moles of a substance

Different molecules have distinct weights that can be determined through mass spectrometry. In addition, molecules are always neutral as they have no positive or negative charge. They are represented by a chemical formula that shows the types of atoms in the molecule. It uses subscripts to show how many of each atom is present. Furthermore, they have low boiling points, melting points, and low solubility. You can observe molecules under electron microscopes but not under student microscopes

Types of Molecules

There are numerous types of molecules, based on no. of atoms involved, the similarity or dissimilarity, and their sizes.

Based on the Number of Atoms

Monoatomic Molecules – consisting of only one atom, for example, Argon, Helium, etc.

Diatomic Molecules – consisting of two atoms per molecule, for example, HCl, Cl2, etc.

Triatomic Molecules – contains three atoms in a molecule, for example, CO3, O3, etc.

Polyatomic Molecules – as the name indicates, this type can have more than three atoms, up to the molecule requirement, for example, glucose, sucrose, etc.

Based on Similarity or Dissimilarity of Atoms

Homoatomic Molecules – consists of atoms of the same elements, chemically combined, for example, hydrogen (H2), Sulfur (S8).

Heteroatomic Molecules – consists of atoms of different elements, chemically bonded together, for example, water (H2O), glucose (C6H12O6), etc.

Based on Size of Atoms

Macromolecules – having large molecular weight, such as proteins, carbs, lipids, etc.

Macromolecules – having comparatively low molecular weight, such as amino acids, fatty acids, etc.

Explanation of a Compound


It is a combination of different atoms or elements chemically bonded together. It is also important to note that all compounds are always molecules, but not every molecule can be a compound. We generally classify compounds into three types based on their bonding: covalent compounds, ionic compounds, and metallic compounds. Moreover, the elements in any compound are always present in fixed ratios; thus, compounds are homogenous, having a particular formula.

Besides, there is no way to separate a compound by physical means; hence, a compound requires special chemical methods of separation, for example, evaporation, crystallization, etc.

Types of Compounds

Compounds can also be of various types, based on their atoms, complexity, nature of components, and bonding.

Based on the Number of Atoms

Diatomic Compounds – a compound with two chemically bonded atoms are diatomic, such as H2, CO, etc.

Triatomic Compounds – a compound with three chemically bonded atoms, such as CO2, H2O, etc.

Polyatomic Compounds – compounds with four or more atoms chemically coupled refer to polyatomic nature, such as CaCO3, NH4NO3, etc.

Based on Complexity

Simple & Complex Compounds – we can differentiate the two terms based on their complexity; for instance, carbon dioxide and carbon monoxide are simple compounds, whereas fructose is a complex one.

Based on the Type of Components

Organic Compounds – any compound with a carbon atom involved is an organic compound, such as hydrocarbons, amines, alcohol, etc.

Inorganic Compounds – compounds excluding the carbon-hydrogen bonding are the inorganic compounds, for example, oxides, halides, etc.

Based on Bonding

Covalent Compounds – consist of compounds bonded through a shared pair of electrons, for example, HCl, H2O, etc.

Ionic Compounds – consists of compounds bonded through the complete transfer of electrons, for instance, NaCl, LiF, etc.

Brief Differences between Molecules and Compounds



These are the results of a chemical combination of two or more atoms.


On the other hand, a compound is formed when different elements join together to present specific properties.



A molecule can be heteroatomic or Homoatomic, based on its type.


Whereas, in contrast, a compound is always a combination of different elements.



These are usually not observed with a naked eye.


On the other hand, compounds are visible to human beings, and we can hold their particles in our hands, for example, sugar crystals.



These are not very stable, and the bonds are easily breakable.


On the contrary, compounds have covalent or ionic bonding in them that makes them highly stable.

Difference in Bonding


These can be bonded through ionic or covalent bonds only.


The nature of a compound is formed from its ionic, covalent, or metallic bonding.


Despite being different, molecules and compounds are most of the time confused by students. So, it was necessary to provide a detailed article on their differences. Both molecules and compounds exist in our surroundings through special bonding but are differentiated based on separation techniques.

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