WASSCE Chemistry · Paper 1 style

Periodic table

One sample question with the full working. 14 more in the app, with instant feedback and repair sessions for the traps below.

Across period 3 from sodium to chlorine, atomic radius

Astays the same because the number of shells is constant
Bdecreases because nuclear charge increases while the electrons enter the same shell
Cdecreases because the number of shells decreases
Dincreases because more electrons are added

Show the answer and working

Answer: B

Greater attraction pulls the outer shell closer.

Trap A Takes one factor as the whole answer: Ask whether the option is necessary or sufficient. If the stem involves two changes or two conditions, both must appear in the answer.

Trap C Periodic trend errors: Across a period: radius decreases, ionisation energy and electronegativity increase (more protons, same shell). Down a group: radius increases, ionisation energy decreases (more shells, more shielding).

Trap D Reverses a trend, direction or effect: State the rule with its direction before looking at the options (down group 1 reactivity INCREASES; exothermic forward reaction: heating shifts LEFT). An option that is the mirror image of the rule is the trap.

Traps in Periodic table

Takes one factor as the whole answer
Ask whether the option is necessary or sufficient. If the stem involves two changes or two conditions, both must appear in the answer.
Periodic trend errors
Across a period: radius decreases, ionisation energy and electronegativity increase (more protons, same shell). Down a group: radius increases, ionisation energy decreases (more shells, more shielding).
Reverses a trend, direction or effect
State the rule with its direction before looking at the options (down group 1 reactivity INCREASES; exothermic forward reaction: heating shifts LEFT). An option that is the mirror image of the rule is the trap.
Picks a related substance or process with a different role
Learn reagents and processes as one-line 'name → job' cards and contrast neighbours in a table (process | product | catalyst | conditions). Match the job in the stem, not just the topic.
Over-generalises a rule beyond where it holds
Every rule in chemistry has conditions. Before applying one, check the conditions in the stem (electrode type, concentration, moles of gas on each side, metal position).
Mixes up a pair of similar chemical terms
Keep a list of confusable pairs with one defining feature each and a hook. Underline the key word in the stem and check it against the definition, not the sound of the name.
Miscounts atoms, electrons or steps
After working, check by counting back: total electrons = atomic number; atoms in the formula match the subscripts; number of half-lives = time ÷ half-life.
Puts a substance or reaction in the wrong class
Classify from the defining feature: functional group for organic series; bond type and structure for properties; reaction with acid AND alkali for amphoteric. Check each option against the feature, not the name.
Uses everyday or macroscopic thinking instead of particles
Ask what the particles, ions or electrons are doing. Properties of a substance come from its particles and bonds, not from how it looks or feels.
Chooses a true but irrelevant statement
Re-read the question word (why, which, what causes). A true fact that answers a different question is still wrong.

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