Grade 9 · Science · Unit 3 of 6
Atoms & Electrons
Shells, valence and the periodic table
What your child practises
Protons, neutrons and electrons, drawing electron shells for the first 20 elements, valence electrons, periodic table groups and periods, and ions and isotopes.
Yukon Curriculum learning standard: Atomic structure and the periodic table: electron arrangement, valence electrons and ions
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
How many electron shells (energy levels) are used by a neutral sodium atom?
- 4
- 5
- 2
- 3
3
Hint: Sodium has 11 electrons arranged 2-8-1, so 3 shells are in use.
Question 2
How many valence electrons (electrons in the outer shell) does sulphur (S) have?
- 7
- 5
- 16
- 6
6
Hint: Sulphur has 16 electrons in shells of 2, 8, 6. The outer shell holds 6.
Question 3
Who proposed that electrons orbit the nucleus in fixed energy levels (shells)?
- Charles Darwin
- Isaac Newton
- Niels Bohr
- Louis Pasteur
Niels Bohr
Hint: The Bohr model arranges electrons in energy levels.
Question 4
Hydrogen (H) has atomic number 1. How many electrons does a neutral atom of it have?
answer box
1
Hint: In a neutral atom, the number of electrons equals the number of protons, which is the atomic number.
Question 5
The elements in Group 18 (the noble gases) rarely react because…
- they have no electrons
- their outer shells are already full
- they are liquids
- they are very heavy
their outer shells are already full
Hint: A full outer shell is stable, so noble gases don't need to gain or lose electrons.
Question 6
Group 1 elements, the alkali metals, are very reactive because they have…
- one valence electron that is easily lost
- eight valence electrons
- a full outer shell
- no neutrons
one valence electron that is easily lost
Hint: Losing one electron gives them a stable arrangement.