Atoms and molecules
3 marks · NormalA molecule of ammonia (NH₃) contains both nitrogen and hydrogen atoms.
Calculate the total number of atoms in two molecules of ammonia (NH₃). Show your working.
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8 atoms
Must show: each calculation step
Also accept: Four atoms per NH₃; two molecules = 8 atoms
Common mistakes: Missing multiplication step; Calculating for one molecule only
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Identifies the number of atoms in one ammonia molecule (4 atoms: 1 N + 3 H).
M1 · 1 mark · Multiplies the atoms by the number of molecules.
A1 · 1 mark · Gives correct total: 8 atoms.
Worked solution
NH₃ has 1 nitrogen atom and 3 hydrogen atoms: total = 1 + 3 = 4 atoms per molecule.
Two molecules: 4 × 2 = 8 atoms.
Final answer: 8 atoms.