Difference Between Molecule and Compound - Definition with FAQs

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.

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.

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.

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:

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