Atoms and Molecules, Difference Between Atoms and Molecules

Table of Contents

Atoms and Molecules

It is the smallest particle of matter which take part in chemical reactions and does not lose its identity.
Atoms are the basic units of matter and the defining structure of elements.
An atom has no independent existence.
Discovered by John Dalton

Structure of an Atom:

An Atom has two basic parts-

A group of two or more than two atoms of the same or different elements that are chemically bonded together is called a molecule.
A molecule can exist independently.
g., H_2,H₂O, O_{2 etc.}

Types of molecules:

Homoatomic molecules-

The molecules of same type of atoms.
For example, a molecule of oxygen consists of two atoms of oxygen to form a diatomic molecule O₂.

Heteroatomic molecules-

The molecules of different type of atoms.
For example, a molecule of carbon di oxide consists of one atom of carbon and two atoms of oxygen to form a triatomic molecule CO₂.

The number of atoms present in a molecule of an element or a compound is known as its atomicity.

S.N	Atoms	Molecule
1	Smallest particle in an Element	Two or more atoms combined together.
2	An atom is made up of neutrons, protons, and electrons.	A molecule of an element or a compound is made up of two or more atoms or the atoms of the constituent elements respectively.
3	Atoms of every element portray a certain degree of reactivity, except the noble elements.	Compared to atoms, molecules are less reactive.
4	Atoms have electrons on the outer shell. Due to this fact atoms may not remain stable all the time.	The formation of molecules take place to attain stability.
5	Example : O , H , P	Example : O2 , H2O , P4 ,

Atomic mass in an atom or group of an atom is the sum of the masses of protons, neutrons and electrons.
The electrons have very less mass in comparison with protons or neutrons so the mass of electrons is not influenced in the calculation.

Atomic mass = Mass of protons + Mass of neutrons + Mass of electrons

Average Atomic mass:

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance.
Average atomic mass = f1M1 + f2M2 +… + fnMn where f is the fraction representing the natural abundance of the isotope and M is the mass number (Atomic mass) of the isotope.
g., Chlorine consists of two major isotopes- ³⁵Cl (75%) and ³⁷Cl (25%).
Hence Average atomic mass of Chlorine is 35.5

Molecular mass: