Difference Between Molecule and Compound

Difference Between Molecule and Compound - Definition with FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:53 PM IST

Molecules and Compound-

Difference between molecule and the compound-

Molecules can define any kind of matter i.e., elements, mixture, or compounds, but the matter is called a compound if it has at least two or more atoms of the same or different elements.
A molecule is a repeating unit for any kind of matter, for example- compound, element, mixture.

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Molecules and Compound-
Compound-
Difference between molecule and compound-
Let us look at the molecules of element and compound-

The chemical composition of any entity can be described based on its building blocks or the repeating unit of a matter. Let us study all such terms used to define matter.

Element- In 1661, Robert Boyle used the term element for the first time. Lavoisier defined an element as the basic unit of matter which is indestructible.

An element is a pure substance that contains atoms of the same substance. Example- Gold, silver, dihydrogen, oxygen, uranium are all elements. I would not call NaCl an element because it has atoms of two different elements i.e., Sodium and Chlorine.
In nature, elements can exist in three ways-

Monoatomic – Elements containing molecules of one atom only. Example- copper, silver, gold, etc.

Diatomic- Elements containing molecules of two atoms. Example- dihydrogen (H₂), oxygen (O₂), nitrogen (N₂).

Polyatomic- Elements containing molecules of two or more two atoms. Ozone is represented as (O₃), phosphorus is represented as (P₄), and Sulphur is represented as (S₈), etc. Chemical properties of elements-

Elements can be of two types- Metals and non-metals and metalloids

Metals are different from non-metals in physical and chemical properties.

Metals are solid and hard at room temperature and non-metals are gases and brittle at room temperature.
Metals are good conductors of electricity whereas non-metals are bad conductors of electricity.
Metals are highly dense and non-metals have low density.

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Compound-

A compound is a pure substance containing molecules of two more atoms of different elements.
It is a pure substance even if contains atoms of two or more than two elements because the building unit is composed of different atoms to form one unit which repeats itself throughout the compound.
A compound is formed from a chemical reaction between two or more elements. The combining elements have to be in a fixed proportion by mass to form a compound.
The elements lose their properties to form this new compound and acquire new physical and chemical properties.
No physical means can separate these elements of the compound.
Carbon dioxide, hydrogen chloride, water, calcium carbonate, etc. are examples of compounds. Carbon dioxide has one atom of carbon and two atoms of oxygen. Hydrogen chloride has one atom of hydrogen and one atom of chlorine. Water constitutes one atom of oxygen and two atoms of hydrogen. Calcium carbonate has one atom of calcium, one atom of carbon, and three atoms of oxygen.

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What is the need for the term “Molecule”?

An atom is the smallest form of matter in nature however, an atom is incapable of existing as a single entity. So, the term molecule is used for the group of two more than two atoms of an element. Therefore the terms elements, molecules, and compounds should not be misunderstood. Each one of these terms has its purpose to serve.

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Molecule Vs Compound-

Looks like both the terms are indicating a bunch of elements bonded together. But what are the defining terms?

Molecule- The term molecule can be used to define the basic unit of an element, or a compound. Just like the term molecule is used to define the composition of water from H₂O molecules, in the same way, the term ‘molecule’ is used to define the composition of gold from Au atoms. Do you notice the slight difference here? The term ‘molecule’ can define the basic unit of the compound water as well as the water compound.

Difference between molecule and element-

An element represents a possibility of nature. Every element represents a set of protons, electrons, and protons. For example- Hydrogen represents one proton, one electron, and one neutron. If you further divide this element then you will get a substance that is no longer an element.
An element does not exist as a single atom but a group of atoms. To define this group of atoms the term molecule was introduced.
The term molecule represents a group of two or more two atoms held together by covalent bonds. These groups of atoms can either be of the same element or two different elements.

Difference between molecule and compound-

Molecule and compound difference is given as follows

A compound is a pure substance whereas a molecule can be a mixture or a pure substance.
A compound is formed from the chemical combination of two or more elements whereas a molecule may exist as the smallest unit of an element or a combination of two or more different atoms of elements.
Compounds are homogenous in their composition whereas molecules may come from a homogenous or a heterogeneous substance.
The elements of a compound can only be separated by chemical methods whereas for the separation of molecules, both physical or chemical methods can be employed depending on where those molecules are coming from.
Elements of a compound lose their properties whereas molecules may represent an element or a compound.

Is water a molecule or compound?

Water is a compound that is formed by the molecules of hydrogen and molecules of oxygen. Molecular elements came together to form this compound. However, water can be called a molecule when H₂O is the building molecule for another compound.

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Let us look at the molecules of element and compound-

Molecular element –

A Molecule of an element is pure, meaning it is composed of two or more atoms of the same element having the same physical and chemical properties. The atomicity of molecular elements may vary from monoatomic, diatomic, or polyatomic. Molecules of elements such as carbon do not have a general structure so their atomicity is complicated.

Molecular compound

Molecules of compounds are formed when atoms of two or more two elements combine in fixed proportions.
Molecular compound examples are carbon dioxide, calcium carbonate, and water. Carbon dioxide has carbon and 2 oxygen atoms as combining elements. Ammonia has one nitrogen and two hydrogen atoms as the combining elements. Calcium carbonate has one calcium, one carbon and three oxygen atoms are combining elements.
Ions are another species of compounds that are formed as a result of the combination of metals and non-metals. These species are charged.
An ion having a positive charge is called a cation and an ion having a negative charge is called an anion. Examples of molecules of compounds existing as ions are sodium chloride, calcium oxide, and magnesium sulfide.
Sodium is a metal and chlorine, a non-metal. The ion of sodium has a positive charge and chloride is the anion of chlorine having a negative charge.

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. What is the chemical identity of a molecule?

The chemical identity of a molecule is a group of two or more two atoms of the same or different elements.

Depending on the similarity of the atoms joined together, these can be called molecules of compounds or molecules of elements.

2. What is the difference between a molecule and a compound?

A compound is formed by the chemical combination of two or more than two molecules of the same or different elements, however, a molecule is a basic unit that can exist independently to form a compound or element.

3. What is molecule of element?

A molecule of the element is a group of two or more atoms of the same element held together by certain forces.

4. What is a molecular compound?

A compound is formed when the atoms of the same element or atoms of two or more elements are combined to form molecules of the compound.

5. Are all compound molecules?

All compounds can be called molecules however it is not possible for all molecules to be called compounds Some molecules may represent an element and the element is no compound. molecules can either represent compounds or an element. Building units of compounds are called molecules of compounds and an even bigger molecule can exist to form another compound. A molecule is the basic unit of matter that can exist independently. Therefore, all compounds can be called molecules.

6. What is the fundamental difference between a molecule and a compound?

A molecule is a group of two or more atoms held together by chemical bonds, while a compound is a substance made up of two or more different elements chemically combined in a fixed ratio. All compounds are molecules, but not all molecules are compounds. For example, O2 is a molecule but not a compound, while H2O is both a molecule and a compound.

7. Can a single atom be considered a molecule?

No, a single atom cannot be considered a molecule. A molecule must consist of at least two atoms bonded together. For example, a single oxygen atom is not a molecule, but two oxygen atoms bonded together (O2) form a molecule.

8. Are all compounds made up of molecules?

No, not all compounds are made up of molecules. Some compounds, like ionic compounds such as sodium chloride (NaCl), exist as a lattice of ions rather than discrete molecules. These are called non-molecular compounds.

9. What is the relationship between elements, compounds, and molecules?

Elements are pure substances made of one type of atom. Compounds are made of two or more different elements chemically combined. Molecules are the smallest unit of a chemical substance that retains its properties, and can be made of atoms of the same element (like O2) or different elements (like H2O, which is also a compound).

10. How can you distinguish between a mixture and a compound?

A compound is a pure substance with a fixed composition and definite properties, formed by chemical bonding between different elements. A mixture, on the other hand, is a physical combination of two or more substances that can be separated by physical means and does not have a fixed composition.

11. What is the difference between a covalent compound and an ionic compound?

Covalent compounds are formed by sharing of electrons between non-metal atoms and exist as discrete molecules. Ionic compounds are formed by the transfer of electrons between metal and non-metal atoms, resulting in a lattice of oppositely charged ions rather than discrete molecules.

12. Can a molecule contain only one type of element?

Yes, a molecule can contain only one type of element. These are called homoatomic or elemental molecules. Examples include O2 (oxygen), N2 (nitrogen), and S8 (sulfur). However, these are not compounds, as compounds must contain more than one type of element.

13. What is the difference between a molecular formula and an empirical formula?

A molecular formula shows the actual number of atoms of each element in a molecule, while an empirical formula shows the simplest whole number ratio of atoms of each element in a compound. For example, the molecular formula of glucose is C6H12O6, while its empirical formula is CH2O.

14. How does the concept of valency relate to molecules and compounds?

Valency is the combining capacity of an atom, which determines how many bonds it can form with other atoms. This concept is crucial in understanding how atoms combine to form molecules and compounds. For example, carbon has a valency of 4, allowing it to form up to four bonds in molecules like CH4 (methane).

15. What role do chemical bonds play in the formation of molecules and compounds?

Chemical bonds are the forces that hold atoms together in molecules and compounds. They determine the structure, properties, and behavior of these substances. The type of bond (ionic, covalent, or metallic) influences whether the substance forms discrete molecules or a continuous lattice structure.

16. How does the law of constant composition apply to compounds but not to all molecules?

The law of constant composition states that a pure compound always contains the same elements in the same proportion by mass, regardless of its source. This applies to all compounds but not necessarily to all molecules. For example, O2 and O3 are both molecules of oxygen but have different compositions.

17. What is the significance of structural formulas in understanding molecules and compounds?

Structural formulas show how atoms are arranged and bonded within a molecule or compound. They provide information about the spatial arrangement of atoms, types of bonds, and functional groups, which is crucial for understanding the properties and reactivity of the substance.

18. How do intermolecular forces differ from the forces within a molecule or compound?

Intermolecular forces are relatively weak attractions between molecules, while intramolecular forces (chemical bonds) within a molecule or compound are much stronger. Intermolecular forces affect physical properties like boiling point, while intramolecular forces determine chemical properties and molecular structure.

19. Can a compound exist without forming molecules?

Yes, some compounds exist without forming discrete molecules. Ionic compounds, such as sodium chloride (NaCl), form a crystal lattice of alternating positive and negative ions rather than individual molecules. These are called non-molecular compounds.

20. How does the concept of polarity apply to molecules and compounds?

Polarity in molecules and compounds arises from an uneven distribution of electron density due to differences in electronegativity between atoms. This can occur in both molecular compounds (like H2O) and some ionic compounds. Polarity affects properties such as solubility and boiling point.

21. What is the difference between a molecular compound and a network solid?

A molecular compound consists of discrete molecules held together by weak intermolecular forces. A network solid, like diamond or quartz, is a compound where atoms are connected in a continuous three-dimensional network by strong covalent bonds, rather than forming individual molecules.

22. How does isomerism relate to molecules and compounds?

Isomerism occurs when compounds have the same molecular formula but different structural arrangements of atoms. This concept applies to molecules and compounds, showing that the arrangement of atoms, not just their types and numbers, is crucial in determining a substance's properties.

23. What is the relationship between molar mass and the concepts of molecules and compounds?

Molar mass is the mass of one mole of a substance. For molecules and compounds, it's calculated by summing the atomic masses of all atoms in the molecule or formula unit. This concept is crucial for stoichiometric calculations involving both molecular and ionic compounds.

24. How do allotropes fit into the concepts of molecules and compounds?

Allotropes are different structural forms of the same element. They can exist as different types of molecules (like O2 and O3) or as different structural arrangements (like diamond and graphite for carbon). Allotropes are not compounds as they contain only one element, but they demonstrate how elements can form different molecular or structural arrangements.

25. What is the significance of the empirical formula in understanding compounds?

The empirical formula represents the simplest whole number ratio of atoms in a compound. It's significant because it provides the basic composition of a compound, which is useful in determining its identity and in calculations involving mass relationships in chemical reactions.

26. How does the concept of oxidation state relate to molecules and compounds?

Oxidation state (or oxidation number) is a concept used to track electron transfers in chemical reactions. It applies to atoms within molecules and compounds, helping to understand their reactivity and bonding behavior. In ionic compounds, it often corresponds to the actual charge on ions.

27. What is the difference between a molecule and a formula unit?

A molecule is the smallest unit of a covalent compound that retains its chemical properties. A formula unit is the simplest representation of the components of an ionic compound in their lowest whole number ratio. For example, H2O is a molecule, while NaCl is described by its formula unit.

28. How do resonance structures relate to molecules and compounds?

Resonance structures are different Lewis structures for the same molecule or ion that cannot be represented by a single Lewis structure. This concept applies to certain molecules and compounds where electron delocalization occurs, affecting their properties and reactivity.

29. What is the role of electronegativity in determining whether a compound is molecular or ionic?

Electronegativity differences between atoms in a compound determine the nature of the chemical bond. Small differences lead to covalent bonds and molecular compounds, while large differences result in ionic bonds and ionic compounds. This concept is crucial in predicting the type of compound formed.

30. How does the octet rule apply to the formation of molecules and compounds?

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons. This principle guides the formation of many molecules and compounds, explaining how atoms combine to form stable structures.

31. What is the significance of bond angles in molecules and compounds?

Bond angles are important in determining the three-dimensional shape of molecules and compounds. They are influenced by factors like electron pair repulsion and hybridization. The shape of a molecule or compound affects its properties, such as polarity and reactivity.

32. How do hydrogen bonds differ from other types of bonds in molecules and compounds?

Hydrogen bonds are a type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (like N, O, or F) and another highly electronegative atom. They are stronger than most other intermolecular forces but weaker than covalent or ionic bonds. Hydrogen bonds significantly affect the properties of compounds like water.

33. What is the difference between a molecular solid and an ionic solid?

A molecular solid consists of individual molecules held together by weak intermolecular forces. An ionic solid is composed of positively and negatively charged ions held together in a crystal lattice by strong electrostatic forces. This difference affects properties like melting point, solubility, and electrical conductivity.

34. How does the concept of hybridization relate to molecular structure?

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which explains the geometry of molecules. It's crucial in understanding the three-dimensional structure of molecules, particularly in organic compounds. For example, the tetrahedral structure of methane (CH4) is explained by sp3 hybridization of carbon.

35. What is the significance of VSEPR theory in understanding molecular geometry?

VSEPR (Valence Shell Electron Pair Repulsion) theory predicts the three-dimensional arrangement of atoms in molecules based on the repulsion between electron pairs. It's essential for understanding the shapes of molecules and how these shapes influence properties like polarity and reactivity.

36. How do dipole moments relate to the structure of molecules and compounds?

A dipole moment results from the uneven distribution of charge in a molecule due to differences in electronegativity between atoms. It's a measure of polarity and affects properties like solubility and boiling point. Some compounds have overall dipole moments (like H2O), while others don't (like CCl4) despite having polar bonds.

37. What is the difference between intramolecular and intermolecular forces?

Intramolecular forces are the strong chemical bonds (covalent or ionic) that hold atoms together within a molecule or compound. Intermolecular forces are weaker attractions between molecules or formula units. Understanding this difference is crucial for explaining physical properties like boiling points and solubility.

38. How does the concept of formal charge relate to molecular structure?

Formal charge is a way of assigning charge to individual atoms in a molecule or polyatomic ion. It helps in determining the most likely Lewis structure and in understanding reactivity. The sum of formal charges in a neutral molecule is zero, while in an ion it equals the overall charge.

39. What is the significance of bond order in molecular compounds?

Bond order represents the number of chemical bonds between a pair of atoms in a molecule. It's related to bond strength and length. Higher bond orders (like triple bonds) are stronger and shorter than lower bond orders (like single bonds). This concept is crucial in understanding molecular stability and reactivity.

40. How do coordinate covalent bonds differ from regular covalent bonds in molecules?

In a coordinate covalent (or dative) bond, both electrons in the shared pair come from one atom (the donor) rather than one from each atom as in a regular covalent bond. This concept is important in understanding the formation of certain molecules and complexes, like NH4+ or metal complexes.

41. What is the relationship between molecular mass and empirical formula mass?

The molecular mass is the sum of the atomic masses of all atoms in a molecule. The empirical formula mass is the sum of the atomic masses in the simplest whole number ratio of atoms. The molecular mass is always a whole number multiple of the empirical formula mass. This relationship is crucial in determining molecular formulas from empirical formulas.

42. How does the concept of isoelectronic species relate to molecules and ions?

Isoelectronic species are atoms, molecules, or ions that have the same number of electrons and often similar properties. This concept helps in understanding trends in properties across different species. For example, CO, N2, and NO+ are isoelectronic.

43. What is the significance of Lewis structures in understanding molecules and compounds?

Lewis structures are diagrams that show the bonding between atoms in a molecule and the lone pairs of electrons. They are crucial for understanding molecular geometry, bond types, and reactivity. Lewis structures help predict properties like polarity and can indicate where reactions are likely to occur.

44. How do atomic radii and ionic radii differ, and why is this important in compound formation?

Atomic radii refer to the size of neutral atoms, while ionic radii are the sizes of ions. Generally, cations are smaller than their parent atoms, while anions are larger. This difference is crucial in understanding the formation and properties of ionic compounds, including their crystal structures and stability.

45. What is the role of electronegativity in determining bond polarity in molecules?

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. The difference in electronegativity between bonded atoms determines the polarity of the bond. This concept is fundamental in predicting molecular polarity, which affects properties like solubility and boiling point.

46. How does the concept of resonance contribute to the stability of molecules and ions?

Resonance occurs when a molecule or ion can be represented by multiple Lewis structures that differ only in the position of electrons. The actual structure is a hybrid of these resonance forms, often leading to greater stability. This concept is crucial in understanding the behavior of many organic and inorganic species.

47. What is the significance of bond energy in molecular compounds?

Bond energy is the energy required to break a chemical bond. It's a measure of bond strength and stability. Understanding bond energies is crucial for predicting the heat of reaction, the stability of molecules, and their reactivity. Generally, stronger bonds (higher bond energy) result in more stable molecules.

48. How do intermolecular forces affect the physical properties of molecular compounds?

Intermolecular forces (like van der Waals forces, dipole-dipole interactions, and hydrogen bonding) determine many physical properties of molecular compounds. They affect melting and boiling points, solubility, and viscosity. Stronger intermolecular forces generally lead to higher melting and boiling points.

49. What is the difference between a structural formula and a molecular formula?

A structural formula shows how atoms are arranged and bonded within a molecule, often using lines to represent bonds. A molecular formula only shows the types and numbers of atoms in a molecule without indicating their arrangement. Structural formulas provide more information about the molecule's geometry and potential reactivity.

50. How does the concept of hybridization explain the geometry of molecules like methane (CH4)?

Hybridization in methane involves the mixing of one s and three p orbitals of carbon to form four equivalent sp3 hybrid orbitals. These orbitals are arranged tetrahedrally, explaining the tetrahedral geometry of methane. This concept is crucial for understanding the three-dimensional structure of many molecules.

51. What is the relationship between molecular structure and physical properties like boiling point?

Molecular structure determines the type and strength of intermolecular forces, which in turn affect physical properties. For example, linear molecules often have lower boiling points than branched isomers due to weaker intermolecular forces. Polar molecules generally have higher boiling points than non-polar molecules of similar mass due to stronger dipole-dipole interactions.

52. How does the concept of electronegativity difference relate to the type of bonding in compounds?

The electronegativity difference between atoms in a bond determines the bond type. Small differences (less than about 0.5 on the Pauling scale) result in non-polar covalent bonds, moderate differences (0.5 to 2.0) lead to polar covalent bonds, and large differences (greater than 2.0) typically result in ionic bonds. This concept is crucial for predicting compound properties and reactivity.

53. What is the significance of molecular orbitals in understanding bonding in molecules?

Molecular orbital theory describes bonding in terms of the combination of atomic orbitals to form molecular orbitals. It provides a more accurate picture of electron distribution in molecules than Lewis structures or VSEPR theory. This theory is essential for understanding concepts like bond order, magnetic properties, and electronic spectra of molecules.

54. How does the octet rule apply to hypervalent molecules, and what are some examples?

The octet rule states that atoms tend to form bonds to achieve eight electrons in their valence shell. However, some molecules, called hypervalent, have central atoms with more than eight electrons. Examples include SF6 and PCl5. These molecules are explained by concepts like expanded octets and d-orbital participation, demonstrating limitations