The Atom
Atoms are the tiny building blocks of matter.
About this topic
An atom is the smallest unit of an element that keeps its chemical identity. It has a tiny, dense nucleus containing positively charged protons and neutral neutrons, surrounded by a cloud of negatively charged electrons. Almost all the mass is in the nucleus, while almost all the volume is empty space where electrons move.
The number of protons defines the element, and in a neutral atom the number of electrons equals the number of protons so that charges cancel. A proton and neutron each have a mass of about 1 atomic mass unit, while an electron is roughly 1/1836 as heavy. If an atom were the size of a football stadium, the nucleus would be about the size of a pea in the centre.
Take a helium atom: two protons and two neutrons in the nucleus, with two electrons outside. Change the proton count to three and you have lithium, a completely different metal. Atoms are the building blocks for everything, from the water in our cells to the silicon in computer chips.
A common misconception is that electrons orbit like planets on neat paths; modern models show probability clouds called orbitals. Another is that atoms are solid balls. Remember that chemical reactions involve electrons, while nuclear changes involve the nucleus.
Key ideas
- Nucleus of protons and neutrons
- Electrons surround the nucleus
- Atoms are mostly empty space
Quick check
Use cases: where The Atom helps
- Homework: review the key idea behind The Atom before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Atom without notes.
- Visual learning: play with the interactive lab to see how The Atom changes when you adjust its inputs.
- Teaching a friend: explain The Atom in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is The Atom?
Atoms are the tiny building blocks of matter.
What will I learn in The Atom?
Nucleus of protons and neutrons. Electrons surround the nucleus. Atoms are mostly empty space.
Is The Atom part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Atom lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Atom?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.