Class 9 2026 Punjab board chemistry ka chapter 2 structure of atom ka notes ki pictures bhaj daen 🥺☺️

Here are some notes on the Structure of Atom for Class 9 Chemistry:

An atom is the smallest particle of an element that can take part in a chemical reaction. It is made up of even smaller particles called subatomic particles.

The three main subatomic particles are:

• Protons: Positively charged particles found in the nucleus (the central part of the atom).
• Neutrons: Neutral (no charge) particles also found in the nucleus.
• Electrons: Negatively charged particles that orbit the nucleus in specific energy shells or orbits.

The number of protons in an atom determines its identity and is called the atomic number (Z). For a neutral atom, the number of electrons is equal to the number of protons.

The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.
Mass Number (A) = Number of Protons + Number of Neutrons

Isotopes are atoms of the same element that have the same atomic number (same number of protons) but different mass numbers (different numbers of neutrons). For example, Carbon-12 and Carbon-14 are isotopes of carbon.

The arrangement of electrons in different shells or energy levels around the nucleus is called electronic configuration. Electrons fill these shells in a specific order, with the innermost shell holding a maximum of 2 electrons, the next 8, and so on.