medium difficulty4 min

Discovery of Subatomic Particles

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

In one line: Proton positive, electron negative, neutron neutral.

Understand it

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.

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.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1For a neutral atom with 11 protons, it has 11 electrons.
2The positive and negative charges balance, so the atom is neutral.

Method you can reuse

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

Visual tip

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

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why is a neutral atom electrically neutral?

Think first, then show answer

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

Common wrong answer

Writing neutron as negative.

Why it loses marks: Neutron has no charge; electron is the negatively charged particle.

Don't mix this up

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

Exam tip

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