Oxygen and sulfur are both in Group 6 of the periodic table. An atom of the most common isotope of oxygen has atomic number 8 and mass number 16. An atom of the most common isotope of sulfur has atomic number 16 and mass number 32. Explain why atoms of oxygen and sulfur have similar chemical properties, and state how the electron arrangement of a sulfur atom differs from that of an oxygen atom.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.2 Atoms · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Both oxygen and sulfur are in Group 6, so each has 6 valence electrons.
The number of valence electrons determines how atoms bond and react, so their chemical properties are similar.
Sulphur has one more electron shell than oxygen.
Its electron configuration is 2, 8, 6.

Examiner tips

  • Mention the group number to justify similar valence electrons. State the key point that valence electrons control chemistry. Show the full electron configuration for sulphur. Keep the answer concise to fit the 4 marks.

Common mistakes

  • Confusing the total number of electrons with valence electrons. Giving the wrong electron configuration (e.g. 2, 8, 8). Forgetting to note that sulphur has an extra shell.

Mark scheme (4 marks)

  1. Both oxygen and sulfur have the same number of electrons in their outermost shell (6 outer-shell electrons)
  2. It is the number of outer-shell electrons that determines chemical properties
  3. A sulfur atom has more electron shells / energy levels than an oxygen atom
  4. Correct electron arrangement stated for sulfur: 2, 8, 6

Key terms in this question

atomic number · mass number · isotope · group

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