An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus containing protons and neutrons, surrounded by electrons. A molecule is made up of two or more atoms bonded together. Molecules exhibit the properties of their constituent elements and can be broken down into atoms. Atoms are the fundamental building blocks that make up all matter in the universe and were formed after the Big Bang. While once thought to be indivisible, atoms can undergo chemical reactions that separate, combine, or rearrange them.

1. • What is an Atom?
• Atom, the smallest unit that matter
can be broken down into without
releasing any electrically charged
particles. Atoms are also the smallest unit
of matter that exhibit the characteristic
properties of an element. As such, the
atom is the fundamental building block
for chemistry.
• Example: Ne, O

2. • What is a Molecule?
• A molecule can be defined as the combinations of two or
more atoms which are held together by chemical bonds. A
molecule is the smallest portion of a substance which
showcases all the properties of the substance. On breaking
down a molecule further, we see properties of the constituent
elements.
• Example: O2, HCl

3. Factor Atoms Molecules
Definition
Most fundamental and smallest part that can
exist of an element.
Two or more atoms chemically bonded
together.
Example
Oxygen – O
Phosphorus – P
Sulphur – S
Hydrogen – H
Oxygen – O2
Phosphorus – P4
Sulphur – S8
Water – H2O
Structure
The smallest particle with properties of an
element.
Combination of two or more atoms.
Stability
An atom may not always be stable in nature due
to the presence of electrons in the outer shells.
Molecules are formed to attain stability.
Constituent Particles Protons, Electrons & Neutrons
Two or more atoms of the same or different
elements
Reactivity
Except for the noble elements, atoms of all
elements showcase a certain level of reactivity.
Compared to an atom, the level of reactivity is
less because some valence points are filled by
electrons of combined elements.

4. • What is an atom and molecule?
• The ‘simple building blocks of matter’ are known as atoms. The
properties of the chemical element are the smallest constituent units of
substance. Molecules are made up of one or more atoms connected by
covalent (chemical) bonds.

5. • Is an atom considered as a
molecule?
• The term molecule is also used
for any gaseous particle in the
kinetic theory of gases,
irrespective of its structure.
Usually, atoms and complexes
related by non-covalent
interactions, such as bonds of
hydrogen or ionic bonds, are not
called independent molecules. It is
normal to have molecules as
elements of matter.

6. • What does atom mean?
• The essential units of matter and the
defining structure of elements are
atoms. The name “atom” derives from
the Greek word for indivisible, since
atoms were once considered to be the
smallest objects in the world and could
not be separated. After the Big Bang,
13.7 billion years ago, atoms were
formed.

7. • Can an atom be created?
• It is difficult to build or kill atoms, because they are
indestructible; it is difficult to divide them into smaller
pieces. This was founded upon the Law of Mass
Conservation. It was later discovered that atoms are
capable of separating into smaller pieces. The division,
mixture, or rearrangement of atoms requires chemical
reactions.

8. • What is the best definition of an
atom?
• An atom is a particle of matter
that describes a chemical
substance in a special way. A single
nucleus, which is normally
surrounded by one or more
electrons, makes an atom. Each
electron is charged negatively. The
nucleus is charged positively, and
comprises one or two particles
such as protons and neutrons that
are relatively strong.