C
CraftExam
high importancemedium8 min

Discovery of Subatomic Particles

Subatomic particles are the smaller particles inside an atom: electrons, protons, and neutrons.

Practice This Concept

Learn the concept

Student-friendly explanation

Electrons have negative charge, protons have positive charge, and neutrons have no charge. Protons and neutrons are present in the nucleus, while electrons are arranged outside the nucleus in shells. At this level, proton and neutron masses are taken as nearly one unit each, while electron mass is very small in comparison.

How to write this in exams

  1. 1

    Start with the exact idea

    Subatomic particles are the smaller particles inside an atom: electrons, protons, and neutrons.

  2. 2

    Then show how to use it

    Read the particle name, recall its charge, recall its location, then connect it with neutrality or mass number if needed.

  3. 3

    Add one concrete example

    In a neutral carbon atom, 6 protons are balanced by 6 electrons, and common carbon has 6 neutrons.

  4. 4

    Avoid this incomplete answer

    Writing neutron as negative is wrong because neutron has no charge; electron is the negatively charged particle.

Definition

Subatomic particles are the smaller particles inside an atom: electrons, protons, and neutrons.

Example

In a neutral carbon atom, 6 protons are balanced by 6 electrons, and common carbon has 6 neutrons.

Rule to remember

Neutral atom rule: number of protons = number of electrons.

Memory hook

Proton positive, electron negative, neutron neutral.

Examples and method

Worked example

For a neutral atom with 11 protons, it has 11 electrons. The positive and negative charges balance, so the atom is neutral.

Method to apply

Read the particle name, recall its charge, recall its location, then connect it with neutrality or mass number if needed.

Diagram support

A labelled atom diagram should show protons and neutrons in the nucleus and electrons in shells.

How CBSE asks it

Questions often ask charge, location, relative mass, or electron count in a neutral atom.

Avoid common mistakes

Common confusion

Students often place protons in shells or write neutrons as negatively charged.

Common wrong answer

Writing neutron as negative is wrong because neutron has no charge; electron is the negatively charged particle.

Exam tip

Remember charge, location, and relative mass together for each particle.

Quick check

Why is a neutral atom electrically neutral?

A neutral atom is electrically neutral because the number of positive protons equals the number of negative electrons, so the charges balance.

Study the discovery of subatomic particles diagram carefully

Use the labelled diagram to keep discovery of subatomic particles clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of discovery of subatomic particles in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on discovery of subatomic particles.

Revision cue

Revise discovery of subatomic particles through the labels before writing the answer.

Answer writing and exam use

1-mark answer

Subatomic particles are the smaller particles inside an atom: electrons, protons, and neutrons.

2-mark answer

Subatomic particles are the smaller particles inside an atom: electrons, protons, and neutrons. Neutral atom rule: number of protons = number of electrons. In a neutral carbon atom, 6 protons are balanced by 6 electrons, and common carbon has 6 neutrons.

3-mark answer

Electrons have negative charge, protons have positive charge, and neutrons have no charge. Protons and neutrons are present in the nucleus, while electrons are arranged outside the nucleus in shells. At this level, proton and neutron masses are taken as nearly one unit each, while electron mass is very small in comparison. Neutral atom rule: number of protons = number of electrons. For a neutral atom with 11 protons, it has 11 electrons. The positive and negative charges balance, so the atom is neutral. Questions often ask charge, location, relative mass, or electron count in a neutral atom. Writing neutron as negative is wrong because neutron has no charge; electron is the negatively charged particle.
MCQ Quiz

Practice this concept with focused MCQs

Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.

10 MCQs5 MinutesInstant Results
Practice This Concept

Help improve this page

Found something confusing, incorrect, or missing?

Practice This Concept