DoAssignment study guide
C2.3 · Locate and compare subatomic particles in a Bohr–Rutherford model
Learn to locate and compare subatomic particles in a bohr–rutherford model through clear examples and targeted practice.
Ontario Grade 9 Science
Chemistry: The Nature of Matter
Ontario Grade 9 Science study topic C2.3
A tiny grain of salt contains an enormous number of atoms, too small to see with our eyes. Scientists use models to show what an atom is like. One common model is the Bohr–Rutherford model. It shows a central nucleus and electrons arranged in shells around it. The key question for this lesson is: Where is each kind of subatomic particle, and how are the particles alike or different? A subatomic particle is a particle smaller than an atom. The three particles in this model are protons, neutrons, and electrons.
What you will learn
- Locate protons, neutrons, and electrons in a Bohr–Rutherford model.
- Compare the particles by their charge and relative mass.
- Use a model to identify how many of each particle it shows.
Start with the model
A Bohr–Rutherford model is a simplified drawing of an atom. The centre is called the nucleus. Protons and neutrons are shown in the nucleus. Electrons are shown on shells around the nucleus. A shell is a model of an energy level where electrons are shown. The shell circles are not solid walls.
In a drawing, the nucleus is usually much larger than the particles themselves would appear compared with the full atom. The model is not to scale. Its purpose here is to help us locate and compare the particles, not to show their actual sizes or paths.
- Protons and neutrons are located in the nucleus.
- Electrons are located on shells around the nucleus.
- A Bohr–Rutherford model is a useful simplification, not a picture of an atom at actual scale.
Compare the three particles
A proton has a positive charge. A neutron has no charge, so it is neutral. An electron has a negative charge. Charge is a property of a particle that can be positive, negative, or neutral.
Protons and neutrons have similar relative masses. An electron has far less mass than either one. Relative mass means comparing how heavy the particles are, rather than giving their masses in everyday units. The model lets us compare both position and these basic properties.
- Proton: in the nucleus, positive charge, relatively large mass.
- Neutron: in the nucleus, no charge, relatively large mass.
- Electron: on a shell, negative charge, much smaller mass.
Read and compare a model
First, find the nucleus at the centre. Identify the proton and neutron symbols or labels inside it. Then look at the shells and count the electrons shown there. Keep the particles' locations separate from their charges: a plus sign tells you about a proton's charge, while the nucleus tells you where it is located.
For example, a model might show six protons and six neutrons in its nucleus, with six electrons on its shells. This gives a clear comparison: the protons and neutrons are together in the centre, while the electrons are outside the nucleus. The counts and labels are information shown by the model.
- Read the labels and positions before comparing particle counts.
- Do not confuse a particle's charge with its location.
- Use the model only for the features it represents.
Evidence and limits
The Bohr–Rutherford model is a way to organize scientific ideas about atoms. It helps learners compare particle locations and properties. Its rings and dots are symbols, not photographs. The model does not show the actual scale of an atom or the detailed behaviour of electrons.
A model is useful when it answers a clear question. For this expectation, the question is where the subatomic particles are and how they compare. A drawing alone is not a new experiment or a measurement. It is a representation used to communicate the arrangement.
- A model is a simplified representation.
- Use it to locate and compare particles, while remembering what it leaves out.
Compare the subatomic particles
| Particle | Location in the model | Charge | Relative mass |
|---|---|---|---|
| Proton | Nucleus | Positive | Large |
| Neutron | Nucleus | Neutral | Large; similar to a proton |
| Electron | Shells around nucleus | Negative | Much smaller |
Worked example
Locate particles in a carbon model
A Bohr–Rutherford model shows six protons and six neutrons in the nucleus. It shows six electrons on shells around the nucleus. Where is each kind of particle, and which particle has the smallest relative mass?
This schematic shows six protons and six neutrons in the nucleus and six electrons in shells. Particle sizes and distances are not to scale.
- Find the nucleusThe model places the six protons and six neutrons in the nucleus at the centre.
- Find the electronsThe six electrons are shown on shells around the nucleus, not inside it.
- Compare relative massElectrons have much less mass than protons or neutrons. Therefore, the electron is the particle with the smallest relative mass.
Answer: Protons and neutrons are in the nucleus. Electrons are on shells around it. The electron has the smallest relative mass.
Check: The locations and the mass comparison agree with the model's particle labels and the standard particle comparison.
Worked example
Compare particles in an oxygen model
An oxygen model shows eight protons, eight neutrons, and eight electrons. Compare the three particle types by location, charge, and relative mass.
This schematic shows eight protons and eight neutrons in the nucleus and eight electrons in shells. Particle sizes and distances are not to scale.
- Compare locationsThe protons and neutrons are together in the nucleus. The electrons are on shells around it.
- Compare chargesProtons are positive, neutrons are neutral, and electrons are negative. Their equal counts do not change the charge of each individual particle.
- Compare relative massesProtons and neutrons have similar relative masses. Each is much more massive than an electron.
Answer: Protons are positive and in the nucleus; neutrons are neutral and in the nucleus; electrons are negative and on shells. Protons and neutrons have similar relative masses, and electrons have much less mass.
Check: The comparison separates location, charge, and relative mass rather than treating them as the same property.
Worked example
Check a model with different particle counts
A model has a nucleus containing eleven protons and twelve neutrons. It shows eleven electrons on shells. Name the particles in the nucleus, describe the electrons' location, and identify which particles have no charge.
This schematic shows eleven protons and twelve neutrons in the nucleus and eleven electrons in shells. Particle sizes and distances are not to scale.
- Identify the nucleus contentsThe stated nucleus contains protons and neutrons. The counts do not change the names or locations of these particle types.
- Locate the electronsThe model shows electrons on shells around the nucleus.
- Identify neutral particlesA neutron has no charge. Protons are positive and electrons are negative, so only neutrons are neutral.
Answer: The nucleus contains eleven protons and twelve neutrons. The eleven electrons are on shells around it. Neutrons have no charge.
Check: The answer uses the given counts and the model's particle locations and charge labels.
Common mistakes and how to avoid them
Putting electrons in the nucleus because they are part of the atom.
Correction: In a Bohr–Rutherford model, electrons are shown on shells around the nucleus.
Thinking a neutron is positive because it is in the nucleus with protons.
Correction: A neutron has no charge. Its location does not give it a proton's charge.
Assuming the circles and dots show the true sizes and distances.
Correction: The model is simplified and not to scale. Use it to compare locations and particle properties.
Lesson summary
- Protons and neutrons are shown in the nucleus.
- Electrons are shown on shells around the nucleus.
- Protons are positive, neutrons are neutral, and electrons are negative.
- Protons and neutrons have similar relative masses; electrons have much less mass.
Check your understanding
Question 1
In a Bohr–Rutherford model, where are neutrons shown?
- On shells outside the nucleus
- In the nucleus
- Only on the outermost shell
- Outside the atom
Show answer and explanation
In the nucleus
Neutrons are shown in the nucleus, together with protons.
Question 2
Which particle has a negative charge?
- Proton
- Neutron
- Electron
- All three
Show answer and explanation
Electron
Electrons have a negative charge. Protons are positive and neutrons are neutral.
Question 3
Which comparison of relative mass is correct?
- An electron has much more mass than a proton.
- A neutron has no mass.
- Protons and neutrons have similar masses, and an electron has much less mass.
- All three particles have the same mass.
Show answer and explanation
Protons and neutrons have similar masses, and an electron has much less mass.
Protons and neutrons have similar relative masses. An electron's relative mass is much smaller.
Key terms
- Bohr–Rutherford model
- A simplified atom model showing a nucleus and electrons arranged on shells around it.
- Nucleus
- The central part of an atom, where protons and neutrons are shown.
- Subatomic particle
- A particle smaller than an atom, such as a proton, neutron, or electron.
- Shell
- A ring used in the model to show an energy level where electrons are placed.
- Relative mass
- A comparison of how heavy particles are compared with one another.
Continue through SNC1W
View the complete SNC1W Ontario Grade 9 Science curriculum and lessons
- C2.2 · Compare atomic models using the evidence behind them
- C2.4 · Relate an element’s periodic-table position to atomic structure
- C1.1 · Assess the life-cycle impacts of materials in consumer products
- C1.2 · Analyse emerging chemical technologies and their impacts
- C2.1 · Investigate how matter properties and changes affect ecosystems
- C2.5 · Investigate element properties and patterns in the periodic table
About this lesson and its review
Published by DoAssignment. This reviewed lesson follows Ontario Grade 9 Science (SNC1W), expectation C2.3. It is a study resource, not an official curriculum publication.
Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.