What is the difference between Atom and Molecule ? - Future Study Point

What is the difference between Atom and Molecule ?

molecules and atoms

What is the difference between Atom and Molecule?


The atom is the smallest indivisible particle of the substance, the atom can not exist independently while a molecule is composed of 2 or more atoms, the molecule is the smallest divisible particle, in chemical reaction atoms are freed from the molecule and combined with other atoms forming new molecules so molecules are the smallest divisible particle which can exist independently and participate in the chemical reaction, a molecule shows the characteristics of a substance.

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Table of content

Definition of the atom
Definition of the molecule
Difference between atom and molecule
Electronic configuration of the atom
Formation of the ion
Examples of atom, molecules and ions

Definition of the atom:

The atom is the smallest indivisible particle of the matter which can not exist independently, atom is of spherical shape, it is composed of three fundamental stable particles protons, neutrons, and electrons. The neutron and protons are located at the centre of the atom known as the nucleus and electrons revolve around the nucleus due to the force of attraction between the positive charge of protons and the negative charge of electrons. Electrons move around the nucleus almost at the speed of light, so their mass is neglected. The mass of the proton is 1836 times of the electron and the mass of the neutron is almost equal to the mass of the neutron(slightly less than the proton), the protons and neutrons altogether are named nucleons because of their existence at the nucleus, one nucleon is assumed as equivalent to one atomic mass unit(U in short), therefore the atomic mass of an atom is equivalent to the sum of the number of protons and neutrons available in the atom. Examples of atoms are H, He, Fe, etc.

Definition of the molecule:

The molecule is the smallest divisible particle of a substance that can exist independently, a molecule is composed of 2 or more atoms, and molecules participate in chemical reactions between two substances. A molecule of the substance shows the characteristics of the substance. Examples of molecules are H2, CO2, Cl2, etc.

Difference between atom and molecule:



The atom is the smallest indivisible particle of the matter
The molecule is the smallest divisible particle of a substance
Atom can not exist independently,
The molecule can  exist independently,
The mass of the atom is the sum of the number of protons and neutrons
The mass of a molecule is the sum of the atomic masses of constituent atoms in it.
Generally, atoms of non-metals can’t participate in chemical reactions but Metalic atoms participate in the chemical reaction
Molecules of substances compulsorily participate in chemical reactions.
The shape of an atom is spherical
Shape of molecules depends on the number of constituent atoms in it
Examples of atoms are H, C, Cl, Fe, etc.
Examples of molecules are H2, CO2, Cl2, etc.

Electronic configuration of the atom:

Electrons in an atom are distributed as per Neil Bohr’s atomic modal 2n² , where n is the number of orbitals,n =1(K orbital),n=2(L orbital),n =3(M orbital), and so on.

We can write electronic configuration or electronic distribution of any element if the atomic number of the atom is given. The atomic number is the amount of the positive charge at the nucleus which is equivalent to the number of protons at the nucleus and since the atom is a neutral particle it is also equal to the amount of surrounding negative charges (i.e number of electrons at the orbitals). The atomic numbers of hydrogen, oxygen, and calcium are 1,8 and 20 respectively.

Hydrogen→ 1

Oxygen→ 2,6

Calcium→  2,8,8,2

Formation of the ion:

An atom is a neutral particle, electrons in its outermost orbital are known as valence electrons, an atom has a tendency to make an octet in its outermost orbital which is known as the valency of the element. When one substance interacts with another substance the atom which has a deficit of electrons to make an octet receives electrons from the atom which has the same number of additional electrons beyond the satisfied inner orbital. The donor atom forms a positively charged ion (cation)after freeing electrons and the atom which gains electrons forms a negative ion(anion).

As an example an atomic number of hydrogen is one,it has only K orbital where 2 electrons are needed to fulfill it completely therefore either it can gain 1 electron to form H(–) ion or loss 1 electron it can form H(+) ion but commonly it forms H(+) ions.

The atomic number of oxygen is 8, it has two orbitals, in the outermost orbital there are 6 electrons, it has a deficiency of  2 electrons in order to fulfill it completely, therefore it gains 2 electrons to form O(–2) ion.

Examples of Atoms and Molecules:

Examples of atoms are H, C, Cl, Fe, etc.

Examples of molecules are H2, CO2, Cl2, etc.

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