Atom is the smallest particle of an element which has capable of independent existence and holding properties of the original substances. The atom retains the physical and chemical properties of the substance to retain same. It will take part chemical reaction. Hope this helps !!

Dalton's Atomic Theory:
According to Dalton's atomic theory, which was proposed by John Dalton in the early 19th century, matter is composed of tiny indivisible particles called atoms. This theory laid the foundation for our understanding of the structure and behavior of matter at the atomic level.
The Smallest Particle:
According to Dalton's atomic theory, the smallest particle that is capable of independent existence is an atom. Here's a detailed explanation:
1. Element:
- An element is a pure substance made up of only one type of atom.
- However, atoms are considered as the basic building blocks of elements.
2. Molecule:
- A molecule is a group of two or more atoms chemically bonded together.
- While molecules are composed of atoms, they are not the smallest particle according to Dalton's atomic theory.
3. Ion:
- An ion is an atom or a group of atoms that has gained or lost electrons, resulting in a positive or negative charge.
- Although ions are formed from atoms, they are not considered as the smallest particle based on Dalton's atomic theory.
4. Atom:
- According to Dalton's atomic theory, atoms are the smallest particle that can exist independently.
- Atoms cannot be further divided into smaller particles without losing their chemical properties.
- Each atom consists of a nucleus (containing protons and neutrons) and electrons orbiting around the nucleus.
Conclusion:
In summary, Dalton's atomic theory states that the smallest particle capable of independent existence is the atom. This theory revolutionized our understanding of matter and formed the basis for further advancements in the field of atomic and molecular science.