Atomic Structure
Atoms have a dense nucleus and orbiting electrons.
About this topic
Atoms have a tiny, dense, positively charged nucleus of protons and neutrons, surrounded by electrons in a vast space. Rutherford's gold foil experiment showed this: most alpha particles passed through, a few bounced back. The atomic number is the number of protons, and the mass number is protons plus neutrons.
If an atom were the size of a football stadium, the nucleus would be a pea at the centre, so atoms are mostly empty space. Carbon-12, for instance, has 6 protons, 6 neutrons and 6 electrons.
Isotopes of an element have different neutron numbers. Electrons occupy specific energy levels, as described by Bohr and later by quantum mechanics. The number of electrons in the outer shell largely determines an element's chemistry and its place in the periodic table.
Students often picture electrons orbiting like planets. This is a useful model, but modern physics describes them as clouds of probability. Another misconception is that atoms are solid balls; the apparent solidity of matter comes from electric repulsion between electron clouds.
Key ideas
- Rutherford's gold foil experiment
- Nucleus holds protons and neutrons
- Most of an atom is empty space
Quick check
Use cases: where Atomic Structure helps
- Homework: review the key idea behind Atomic Structure before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Atomic Structure without notes.
- Visual learning: play with the interactive lab to see how Atomic Structure changes when you adjust its inputs.
- Teaching a friend: explain Atomic Structure in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Atomic Structure?
Atoms have a dense nucleus and orbiting electrons.
What will I learn in Atomic Structure?
Rutherford's gold foil experiment. Nucleus holds protons and neutrons. Most of an atom is empty space.
Is Atomic Structure part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Atomic Structure 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 Atomic Structure?
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.