Atomic number and mass number
4 marks · NormalThe table below shows information about three atoms.
| Atom | Atomic number | Mass number |
|---|---|---|
| A | 6 | 14 |
| B | 8 | 16 |
| C | 11 | 23 |
For atom A, state the number of protons, neutrons and electrons (assuming atom A is neutral).
Which atom in the table has the greatest number of neutrons? Show your reasoning.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Protons: 6, Neutrons: 8, Electrons: 6
(b) Atom A (has 8 neutrons), with working shown for all three atoms
Common mistakes: Mixing up protons and neutrons; Not showing reasoning in part b
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States number of protons (6) and electrons (6) for atom A.
B2 (a) · 1 mark · Calculates number of neutrons for atom A as 14 – 6 = 8.
M1 (b) · 1 mark · Calculates number of neutrons for all atoms (A: 8, B: 8, C: 12).
A1 (b) · 1 mark · Identifies atom C as the atom with the greatest number of neutrons (12).
Worked solution
a) Atom A: Protons = atomic number = 6. Electrons = 6 (neutral atom). Neutrons = 14 – 6 = 8.
b) Number of neutrons: Atom A: 14 – 6 = 8. Atom B: 16 – 8 = 8. Atom C: 23 – 11 = 12. Atom C has the greatest number of neutrons (12).