Structure of Atom Notes

Title:
"Unlocking the Secrets of the Atom: Complete Class 9 Study Notes with Simple Definitions &
Important Questions"



Chapter: Structure of Atom

Introduction to the Atom

An atom is the smallest unit of matter that retains the properties of an element. Everything
around us, including air, water, and solid objects, is made of atoms. The structure of an atom is
made up of tiny subatomic particles that move within specific regions.



Basic Subatomic Particles

Atoms are made up of three fundamental subatomic particles:

1. Protons
o Definition: Protons are positively charged particles found in the nucleus (center)
of an atom.
o Charge: Positive (+1)
o Mass: 1 amu (atomic mass unit)
o Symbol: p+
2. Neutrons
o Definition: Neutrons are neutral particles, meaning they have no charge, and are
also located in the nucleus.
o Charge: Neutral (0)
o Mass: 1 amu
o Symbol: n0
3. Electrons
o Definition: Electrons are negatively charged particles that revolve around the
nucleus in defined energy levels or shells.
o Charge: Negative (-1)
o Mass: 1/1836 amu (very small compared to protons and neutrons)
o Symbol: e-




Structure of an Atom

The structure of an atom can be broken down into two main regions:

1. Nucleus