Inside the Atom - Protons, Neutrons and Electrons
You'll be able to label a simple atom model.
Three subatomic particles, and how their numbers decide which element you have and how it behaves.
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Text description
- In the nucleus: the proton has a positive charge; the neutron has no charge; both have a similar mass; they are held together by the strong nuclear force.
- Outside the nucleus: the electron has a negative charge; it is much lighter than the nucleus particles; electrons are found in electron shells and determine chemical reactivity.
- Subatomic particles differ in charge, mass and location within the atom.
Text description
- Nucleus in the centre: protons and neutrons.
- Electrons outside the nucleus.
- Key: proton (+), neutron (0), electron (−).
- Simplified model, not to scale.
Q1 · What do you already know about what's inside an atom?
Q2 · If atoms are described as "mostly empty space", why can't your hand pass straight through a table?
● Know
- atoms contain protons, neutrons and electrons
- protons and neutrons are in the nucleus
- electrons are found outside the nucleus
● Understand
- particle charge helps distinguish the three particles
- simple atomic models show location, not exact scale
- the nucleus is small but important
● Can do
- label a simple atom model
- compare charge and location of subatomic particles
- avoid mixing up neutron with neutral atom
Press your finger on a desk and you feel solid resistance. Whatever produces that resistance is happening inside atoms, and every atom is built from just three kinds of particle. Telling them apart is what this lesson is for. A proton carries a positive charge and sits in the nucleus, the small dense centre of the atom. A neutron carries no charge and also sits in the nucleus. An electron carries a negative charge and is found outside the nucleus.
Protons and neutrons are far heavier than electrons, so the nucleus holds almost all of the atom's mass. An atom's mass is therefore set by what is in its nucleus, while its size is set by how far out its electrons reach. Those two things are decided by different particles, which is why the next lessons treat them separately.
Text description
- Nucleus: 3 protons (+1 each) and 4 neutrons (0).
- Shell 1: 2 electrons (−1 each). Shell 2: 1 electron.
- Li: Z = 3, A = 7.
A hydrogen atom has 1 proton in its nucleus and 1 electron outside. A carbon atom has 6 protons, 6 neutrons and 6 electrons. The protons and neutrons are packed into the nucleus, while the electrons move in the space around it. If you could peer inside, you would see a tiny central cluster with almost everything else empty.
Australian research: Scientists at ANSTO use particle accelerators to study the structure of atomic nuclei. Their work helps develop medical isotopes for cancer treatment and advanced materials for industry, all built on understanding protons, neutrons and electrons.
'A neutron is the same thing as a neutral atom.' It is not. A neutron is a single particle inside the nucleus, and it carries no charge. A neutral atom is a whole atom whose charges balance, because it has as many electrons as protons. One is a part; the other is the whole thing built from those parts. An atom can be neutral while containing no neutrons at all, which is exactly the case for ordinary hydrogen.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
Use the Subatomic Particle Builder interactive below. What is one thing you learned from using it?
Of the two clues you are given, only one settles the question by itself. Location does not: protons and neutrons share the nucleus, so knowing a particle sits in the nucleus narrows three possibilities to two and then stops. Electrical charge does, because no two of the three carry the same charge.
Test that against all three and it holds: (+1) identifies a proton, (0) identifies a neutron, (−1) identifies an electron. Each value maps to exactly one particle, so a second check adds nothing. That is why the diagram above labels the particles themselves p+, n0 and e⁻.
Location is still worth reading, because it answers a different question: which particles are bound together at the centre and which one is free to move in the space outside. Use charge to name the particle; use location to picture where it sits.
A particle reads (−1): that is an electron, and it lies outside the nucleus. A particle reads (0): a neutron, in the nucleus. A particle reads (+1): a proton, also in the nucleus. In each case the charge named the particle first, and its location followed from the name.
Australian physics: Researchers at the University of Melbourne study particle interactions using charge as the primary identifier, just as students do in this lesson. Charge is one of the most fundamental properties in all of physics.
'Neutrons are neutral, so they do not matter.' Neutrons add mass and contribute to the binding of nuclei that contain multiple protons, helping offset the electrical repulsion between those protons. Ordinary hydrogen-1 (protium) has one proton and no neutron; hydrogen-2 (deuterium) has one neutron, and hydrogen-3 (tritium) has two. So neutron counts can vary between isotopes of the same element.
- Proton
- Neutron
- Electron
- Nucleus, positive charge
- Nucleus, no charge
- Outside nucleus, negative charge
The nucleus sits at the centre, but the whole atom extends far beyond it. An atom's diameter is roughly 100,000 times its nucleus's diameter, and nearly all of that space contains nothing but the moving electrons. A drawing that crams every particle into one cluster has lost the feature that matters most.
This is why a simple atom diagram is worth drawing even though its scale is wrong. It shows which particles exist, what charge each carries and where each one sits, which is what you are asked to reason about. What it cannot show is the emptiness: a nucleus drawn to true scale would be too small to see on the page.
Enlarge an atom to the size of a football stadium and its nucleus would be a fly on the centre circle, with the electrons as specks somewhere out around the stands. Everything in between is empty. That is the structure of every solid object you have ever touched.
Australian Synchrotron: The Australian Synchrotron in Melbourne uses our understanding of atomic structure to study materials at the molecular level. Researchers there have helped develop better pharmaceuticals, more efficient solar cells and stronger industrial materials.
'Atoms are mostly solid matter.' They are not. Atoms are almost entirely empty space. The reason your hand does not pass through a table is not because atoms are solid, but because of electrostatic repulsion between the electrons in your hand and the electrons in the table. Both are mostly empty, but their electron clouds push against each other.
If an atom were the size of a football stadium, how big would the nucleus be?
How close was your prediction?
Nice calibration, your intuition is good for this kind of problem.
Good, being surprised is the point. This answer is worth remembering.
Sort the statements positive, no charge, negative, nucleus and outside nucleus under the correct particle names.
Most early mistakes come from mixing together three different facts.
For example, some you say electrons are neutral, or place electrons in the nucleus. Others think neutrons are the same thing as neutral atoms. Each of these ideas should be corrected directly.
A strong answer names the particle, gives its charge, and gives its simple location.
Draw a simple atom model and label proton, neutron, electron and nucleus. Then explain which part of the diagram is not drawn to true scale.
At the start of this lesson, you were asked about the atom being almost entirely empty space yet your chair still holding you up, and what three subatomic particles give every element its identity.
Now that you have worked through everything, write your answer below. How has your thinking changed, and what surprised you most?
Q1. Define proton, neutron and electron using charge and location.
Q2. Explain why a simple atom model is useful even though it is not perfectly realistic.
Q3. A student says electrons are in the nucleus because they are part of the atom. Explain why this is incorrect.
Model answers (click to reveal)
Model Answers
-Multiple Choice
1: A. A proton has a positive charge.
2: C. Protons and neutrons are found in the nucleus.
3: B. Electrons are negatively charged.
4: D. A simple model is useful because it clearly shows the main parts and positions.
5: A. A neutron has no charge and is found in the nucleus.
Short Answer 1
A proton is positive and found in the nucleus. A neutron has no charge and is also found in the nucleus. An electron is negative and is found outside the nucleus.
Short Answer 2
A simple atom model is useful because it shows the main parts of the atom clearly and helps scientists and you communicate ideas about structure. It does not need to be perfectly realistic to be useful.
Short Answer 3
The statement is incorrect because electrons are modelled outside the nucleus, not inside it. The nucleus contains protons and neutrons. A strong model keeps particle name, charge and location separate.
Model answers (click to reveal)
Model Answers
-Multiple Choice
1: A. A proton has a positive charge.
2: C. Protons and neutrons are found in the nucleus.
3: B. Electrons are negatively charged.
4: D. A simple model is useful because it clearly shows the main parts and positions.
5: A. A neutron has no charge and is found in the nucleus.
Short Answer 1
A proton is positive and found in the nucleus. A neutron has no charge and is also found in the nucleus. An electron is negative and is found outside the nucleus.
Short Answer 2
A simple atom model is useful because it shows the main parts of the atom clearly and helps scientists and you communicate ideas about structure. It does not need to be perfectly realistic to be useful.
Short Answer 3
The statement is incorrect because electrons are modelled outside the nucleus, not inside it. The nucleus contains protons and neutrons. A strong model keeps particle name, charge and location separate.
● Particles
Atoms contain protons, neutrons and electrons.
● Charge
Positive, no charge and negative help separate the particles.
● Location
The nucleus contains protons and neutrons, while electrons are outside it.
● Bridge Forward
Next lesson turns this structure into atomic number and mass number.