Molecule: Definition, Types, Differences between Atoms and Molecules

You have landed on the right page to learn about Molecule. We studied that the smallest portion of matter is known as an atom, and it is extremely small in size. In general, the atoms of the majority of elements do not exist on their own. The exceptions are the elements of inert gases (also known as noble gases). The atoms helium \(({\rm{He}})\), neon \(({\rm{Ne}})\), and argon \(({\rm{Ar}})\), for example, can exist independently.

What about the atoms of other elements? Atoms of the same or different elements are tightly bonded together by strong forces of attraction known as chemical bonds. Molecules are the new species formed as a result of this chemical combination. To learn more about the molecule, read the below article.

Define Atom

“An atom is the smallest particle of an element that possesses all of those properties of element.”

It may or may not exist independently. Atom is the smallest possible unit of an element. Atoms of the same element are all identical. They differ from the atoms of other elements.

The term atom is derived from the Greek word atomos, which means “indivisible,” and was coined by the Greek philosopher Democritus \((460 – 361{\rm{ B}}{\rm{.C}}{\rm{.) }}\). He developed the theory that the universe was made up of tiny, indivisible particles known as atoms. In \(1808\), an English scientist named John Dalton proposed that an atom is the fundamental unit of matter.

For example, Break up a small piece of zinc into smaller pieces. All of these pieces exhibit zinc properties. When crushed pieces are ground further, they break up into very fine particles that retain the properties of zinc. However, there comes the point when the particles cannot be further subdivided into particles with zinc properties. These indivisible particles are zinc atoms.

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Define Molecule

A molecule is a group of two or more atoms (either the same or different) that are chemically bonded to each other and held together by strong, attractive forces. Molecules are represented by symbols of the constituent atoms, which is known as a chemical formula. The forces which hold the atoms together in a molecule are called covalent bonds. Thus: a combination of atoms is called a molecule. Molecules can exist in the state because they are very stable.

For example,

The molecular formula is a representation of the type and the actual number of constituent atoms in a molecule of a substance.

Classification of Molecules

Molecules can be formed either by the combination of atoms of the ‘same element’ or of ‘different elements’. Depending on this, there are two types of molecules: molecules of elements and molecules of the compound.

1. Molecules of Elements

The molecule of an element contains two or more similar atoms chemically combined together.

For example, a hydrogen molecule is made up of two hydrogen atoms, denoted by the symbol \({\rm{H}} – {\rm{H}}\). The chemical bond is represented by the line drawn between the two atomic symbols. The formula of a molecule of hydrogen is written as \({{\rm{H}}_2}\). This formula summarises all of the properties of the element hydrogen.

Similarly, nitrogen gas is made up of \({{\rm{N}}_2}\) molecules, oxygen gas is made up of \({{\rm{O}}_2}\) molecules, and chlorine gas is made up of \({\rm{C}}{{\rm{l}}_2}\) molecules. The bromine element, a liquid, is made up of \({\rm{B}}{{\rm{r}}_2}\) molecules, while the iodine element, a solid, is made up of \({{\rm{I}}_2}\) molecules.

Atomicity of a Molecule of an Element

1. The number of atoms bonded in a molecule of an element is referred to as its atomicity.
2. The atomicity of an element is indicated by writing the number of constituent atoms on the bottom right corner of its symbol.
For example, the atomicity of a hydrogen molecule \(\left( {{{\rm{H}}_2}} \right)\) is represented by the number \(2\). As a result, we refer to hydrogen molecules as diatomic.

Classification of Molecules of Elements based on Atomicity

Elements are classified as monoatomic, diatomic, triatomic, or polyatomic based on the number of atoms in a molecule.

a. Monoatomic molecules of elements: Monoatomic molecule is composed of only one atom. For example, inert gases like Helium, Neon, Argon, etc.

b. Diatomic Molecules of Elements: A molecule containing two atoms is called a diatomic molecule. The atomicity of each diatomic molecule is \(2\).

For example, a molecule of hydrogen is made from two atoms of hydrogen. Therefore, its atomicity is two and is represented as \({{\rm{H}}_2}\).

c. Triatomic Molecules of Elements: A molecule containing three atoms is called a triatomic molecule. Ozone is a triatomic molecule with the formula \({{\rm{O}}_3}\) and the atomicity of \(3\).

d. Polyatomic Molecules of Elements: The molecules containing four or more atoms of the same element are called polyatomic molecules.

For example,

1. Phosphorus exists as a tetratomic molecule and is denoted by the symbol \({{\rm{P}}_4}\).
2. Sulphur exists as an octatomic molecule, denoted by the symbol \({{\rm{S}}_8}\).
3. Boron has \(12\) atoms and is abbreviated as \({{\rm{B}}_{12}}\).
4. Fullerene (a new allotrope of carbon) has \(60\) atoms and is denoted by the symbol \({{\rm{C}}_{60}}\).

2. Molecules of Compounds

A molecule of a compound is composed of two or more atoms of different elements in definite proportions.  These atoms are chemically bonded in a molecule. The molecules of compounds may also be diatomic, triatomic, tetra-atomic and polyatomic in nature, depending upon the number of the atoms linked or combined by chemical bonds. The molecules of the compounds are heteroatomic in the sense that they contain different atoms.

For example, a methane \(\left( {{\rm{C}}{{\rm{H}}_4}} \right)\) molecule, which is a compound, is heteroatomic in nature. The compound which consists of molecules is called a molecular compound. Hydrogen chloride, water, carbon dioxide, sulphur dioxide: methane, and ammonia are all molecular compounds.

Examples of molecules of a compound are as follows:

1. Hydrogen chloride is a compound. The atoms in hydrogen chloride \(({\rm{HCl}})\) molecule are of two types: hydrogen \(({\rm{H}})\) and chlorine \(({\rm{Cl}})\).
2. Water is an example of a compound. A water molecule \(\left( {{{\rm{H}}_2}{\rm{O}}} \right)\) is made up of two types of atoms: hydrogen atoms \(({\rm{H}})\) and oxygen atoms \(({\rm{O}})\).
3. Carbon dioxide \(\left( {{\rm{C}}{{\rm{O}}_2}} \right)\) is a compound with two types of atoms in its molecule: carbon atoms \(({\rm{C}})\) and oxygen atoms \(({\rm{O}})\).

4. Here are some more examples of compound molecules: Sulphur dioxide \(\left( {{\rm{S}}{{\rm{O}}_2}} \right)\), methane \(\left( {{\rm{C}}{{\rm{H}}_4}} \right)\), and ammonia \(\left( {{\rm{N}}{{\rm{H}}_3}} \right)\).

Atomicity of a molecule of a compound: The total number of all types of atom in one molecule of a compound is called its atomicity. Thus,

Differences between Atom and Molecule

Summary

A molecule is a group of two or more atoms (either the same or different) that are chemically bonded to each other and held together by strong attractive forces. Molecules can be formed either by the combination of atoms of the ‘same element’ or of ‘different elements’. Depending on this, there are two types of molecules: molecules of elements and molecules of compound.

FAQs

Q.1. What does molecular compound mean?
Ans: The compound which consists of molecules is called a molecular compound.

Q.2. What are 3 examples of molecules?
Ans: The three examples of molecules are, Water, carbon dioxide and Hydrogen chloride.

Q.3. What is the difference between atoms and molecules?
Ans: The difference between Atoms and molecules is as follows:

Q.4. What is molecule of an element?
Ans: A molecule is a group of two or more atoms (either the same or different) that are chemically bonded to each other and held together by strong attractive forces.

Q.5. What is the smallest molecule?
Ans: The diatomic hydrogen \(\left( {{{\rm{H}}_2}} \right)\) molecule is the smallest molecule.

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