Grade 9 · Science · Unit 5 of 11
Inside the Atom
Particles, models and shells
What your child practises
Protons, neutrons and electrons, how Dalton, Thomson, Rutherford and Bohr's models changed with evidence, atomic and mass numbers, and drawing the electron shells of the first 20 elements.
Ontario Curriculum expectation: C2.2, C2.3 · evidence for atomic models, and the location, mass and charge of subatomic particles in the Bohr–Rutherford model
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A neutral atom has electrons arranged 2, 4. How many protons are in its nucleus?
answer box
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6
Hint: Add the electrons: 2 + 4 = 6. A neutral atom has the same number of protons.
Question 2
Which particle has a mass that is very small compared with the others?
- electron
- neutron
- nucleus
- proton
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electron
Hint: Almost all of an atom's mass is in its nucleus.
Question 3
A neutral atom has the same number of…
- protons and neutrons
- protons and electrons
- neutrons and electrons
- shells and protons
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protons and electrons
Hint: Equal positive and negative charges cancel.
Question 4
Carbon-12 and carbon-14 both have 6 protons. How do they differ?
- They have different numbers of shells
- They have different numbers of neutrons
- They are different elements
- They have different numbers of protons
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They have different numbers of neutrons
Hint: Atoms of the same element with different numbers of neutrons are isotopes.
Question 5
An atom's mass number is the number of…
- protons plus neutrons
- protons only
- shells
- electrons only
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protons plus neutrons
Hint: Electrons add almost no mass.
Question 6
Which shows the electrons in each shell (Bohr–Rutherford) of a neutral lithium atom (atomic number 3)?
- 2
- 2, 3
- 2, 2
- 2, 1
Show answer
2, 1
Hint: A neutral atom has 3 electrons. Fill the shells in order: 2, then 8, then 8. That gives 2, 1.