A simple summary of difference between molecule and compounds is given below

1DefinitionMolecules are two or more atoms bonded togethercompounds are two or more different elements bonded together
2RelatednessAll molecules are not compounds.All compounds are molecules.
3StructureThey are group of bonded atomsThey are matter in complete shape (i.e. table salt)
4VisibilityThey are not visible to humansThey are visible to humans
5ExampleOzone (O3), water (H2O)table salt (NaCl), calcium carbonate (CaCO3)

What is Molecule?

A molecule is a group of atoms bonded together by a chemical bond that are the smallest fundamental unit of a chemical compound or matter and have all the properties of that matter. Molecules are formed by the chemical reaction of atoms. The atoms in molecules are held together by shared electron pairs or covalent bonds.

The molecular mass of molecular is called molecular weight or gram molecular mass or mole. which is the sum of the atomic weights of its component atoms. The system international unit of molecular mass is kilogram per mole and the formula is M= m/n

Where M= molar mass

 m is mass of a substance (in grams)

n = number of moles of a substance

Different molecules have different molecular weights. Molecular weights can be determined by mass spectrometry. It can also be measured by techniques based on thermodynamics or kinetic transport phenomena.

Molecules are always neutral they have no positive or negative charge. They are represented by a chemical formula that shows the types of atoms in the molecule. This uses subscripts, to show how many of each type of atom is present. They have low boiling, melting points, and low solubility

Types of molecules

There are following types of molecules based on the number of atoms per molecules

Monoatomic molecules

Molecules having only one atom is called monoatomic molecules e.g. Ar, Hi.

Diatomic molecules

Diatomic molecules contain two atoms per molecule e.g. HCL, Cl2.

Triatomic molecule

These molecules contain three atoms per molecule e.g. CO2, O3.

Polyatomic molecules

There are many atoms per molecule in the polyatomic molecules e.g. C6 H12 O6 etc.

Molecules may be homonuclear or heteronuclear molecule

Homoatomic Molecule

A homoatomic molecule consists of atoms of the same elements chemically combined e.g. hydrogen (H2), Sulfur (S8).

Heteroatomic Molecules

When molecules consist of atoms of different elements are called heteroatomic molecules e.g, water (H2O), glucose (C6 H12 O6).

In biology molecules are of two types


Molecules having large molecular weight are called macromolecules such as proteins, lipids, etc.


Molecules having low molecular weight are called macromolecules such as amino acids, glucose,etc.

What is Compound?

Compounds are substances that are atoms and different elements united together by the chemical bond. The chemical bond in compounds can be covalent or ionic or metallic. The elements in any compound are always present in fixed ratios thus compounds are homogenous in nature.

The properties of a compound are different from the properties of the elements from which it is formed and these constituents cannot be separated by simple physical processes.

Types of compounds

Based on bonding compounds are of two types

Ionic compounds

ionic compounds also called salt compounds that are held together with ionic bonds. They form a crystal lattice in which an ion is surrounding by a definite number of opposite charges. Their chemical formula is represented as formula units. Examples of ionic compounds are NaCl, CuSO4.

Covalent compounds

They are called molecular compounds in which atom binds each other through covalent bonds. Their chemical formula is called molecular formula for example H2 SO4 etc.

Sana Riaz

Sana has just completed her MPhil in Microbiology. She loves reading books and the latest discoveries in sciences.

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