Describe how scientists' understanding of atomic structure changed with the development of the nuclear model of the atom, and state one property of the nucleus.

Eduqas GCSE Chemistry — C1 Atomic structure and the periodic table · Describe · 4 marks · View as Markdown

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

Early scientists believed that the atom was a solid sphere of positive charge with electrons embedded throughout it. Later experiments led to a new model being proposed.

Model answer (4 marks)

The earlier plum‑pudding model described the atom as a uniform, solid sphere of positive charge with electrons embedded throughout it.
The nuclear model placed most of the positive charge and the mass in a small central nucleus.
Electrons are now understood to orbit or be found in shells around the nucleus.
One property of the nucleus is that it is very small compared with the atom.

Examiner tips

  • Use the exact phrases from the mark scheme – e.g. "plum‑pudding model", "nuclear model", "electrons orbit", "very small".
  • Show the progression from the old to the new model in clear, separate points.
  • Include a correct property of the nucleus to gain the final mark.

Common mistakes

  • Mixing up the order of the models or using vague terms like "cloud" instead of "orbit".
  • Failing to mention that the nucleus is small or positively charged.
  • Using the wrong spelling of "plum‑pudding" or omitting the word "nucleus".

Mark scheme (4 marks)

  1. The earlier (plum pudding / Thomson) model described the atom as a uniform / solid sphere of positive charge with electrons embedded in it
  2. The nuclear model placed most of the positive charge / mass in a small central nucleus
  3. Electrons orbit / are found around the outside / in shells around the nucleus
  4. One correct property of the nucleus: it is very small / it is positively charged / it contains protons (and neutrons) / it contains most of the mass of the atom

Key terms in this question

nuclear model · nucleus

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