IGCSE 0625 / Section 5.1.1 / Core

A speck of mass in empty space.

If an atom were the size of a stadium, its nucleus would be a pea on the centre spot. Almost all the matter you touch is, on this scale, empty space wrapped around a tiny, heavy core.

The key idea

An atom is mostly empty space, with a tiny, dense, positively charged nucleus of protons and neutrons at the centre and electrons orbiting around it. Almost all the mass of the atom is in the nucleus.

Definition · learn the exact words

An atom has a tiny, dense, positively charged nucleus of protons and neutrons at its centre, with negatively charged electrons orbiting around it.

nucleus = protons + neutrons (positive); electrons orbit (negative)

Most of the atom is empty space, yet nearly all its mass is in the nucleus.

Section 01

Look inside the atom.

Explore the nucleus and the orbiting electrons, and see how little of the atom is actually filled.

Stage 1 · Learn

Check atomic structure

Four quick checks. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

The nucleus of an atom is...

Quick check+10 XP

The nucleus is made of...

Quick check+10 XP

Electrons in an atom...

Quick check+10 XP

Most of an atom is...

Section 02

Tiny core, huge space.

The nucleus is thousands of times smaller than the atom but holds almost all the mass.

Examiner trap

Nearly all the mass of an atom is in the nucleus, even though the nucleus is thousands of times smaller than the atom. The electrons fill the volume but contribute almost no mass.

Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.

Finish the four checks above to unlock the exam questions
Exam style+20 XP

Almost all the mass of an atom is found in...

Exam style+20 XP

The overall charge on the nucleus is...

Exam style+20 XP

Compared with the whole atom, the nucleus is...

Skill unlocked

Atomic structure, mastered.

The nuclear atom is mapped. Keep the chain going.

-Rank -Level -Score -Topics
Go deeper · practice
Six original Cambridge-style questions
The nuclear model: a tiny dense positive nucleus of protons and neutrons with orbiting electrons, and where the mass lies. Attempt each, then reveal the worked solution.
Stage 3 · master the unit
Nuclear physics challenge
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just atomic structure.
Start the unit challenge →