Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

7.3Chapter 7: Inside Atoms

Finding the nucleus — Alhussan Chemistry - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 6 2 quizzes

📚 Alhussan Chemistry - Stage 8 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

7.3 Finding the nucleus — Rutherford's Gold Foil Experiment — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe the gold foil experiment and explain what it showed about the structure of the atom and how scientists build on each other's work.Background — Tho…

  • Prediction
  • Collaboration
  • Experimental design
  • Rate of bounce back
  • Empty space
  • Explaining the results

Part 1 of 5Testing the plum pudding model

Background
  • Thomson's model had good evidence for negative electrons, but no evidence for their arrangement in a positive sphere.
  • Ernest Rutherford lived in New Zealand until he was 23 and moved to England in 1895 to study under Thomson.
Prediction
  • Prediction if the plum pudding model is correct, most positive particles fired at gold foil go straight through.
  • A few would pass close to negative electrons and change direction slightly.
Collaboration
  • Rutherford worked with Hans Geiger and Ernest Marsden.

Part 2 of 5Observations and conclusions

ObservationConclusion
Most particles passed straight throughThe atom is mostly empty space
Some particles were deflectedThe nucleus has a positive charge and repels positive alpha particles
A few bounced backThe positive charge and most mass are concentrated in a tiny, dense nucleus
Rate of bounce back
  • Rate of bounce back around one in every 10 000 particles bounced backwards off the foil.
  • Rutherford said this was as incredible as firing an artillery shell at tissue paper and having it come back.
Result
  • Result the prediction based on the plum pudding model was wrong, so the model must be wrong.

Part 3 of 5Rutherford's nuclear model (1911)

Nucleus
  • Nucleus atoms have a central, positively charged nucleus containing most of the mass.
Empty space
  • Empty space the nucleus is surrounded by empty space in which electrons move.
  • The nucleus is much smaller than the atom, about 10 000 to 100 000 times smaller.
Explaining the results
  • Explaining the results particles that went straight through passed through the empty space between nuclei.
  • The particle that bounced back hit a nucleus.

Part 4 of 5Inside the nucleus

Protons
  • Rutherford fired positive particles into the air and made tiny new positive particles from the nuclei of nitrogen atoms, which were protons.
Neutrons
  • Neutrons the next year he suggested the nucleus also holds particles with mass but no charge.
  • By 1932 James Chadwick showed that a nucleus contains neutrons as well as protons.
Model today
  • Model today positive protons and neutral neutrons in the nucleus, with negative electrons orbiting outside.

Part 5 of 5How scientists build on each other's work

Publication
  • Rutherford published a paper describing his model and the problems with the plum pudding model.
Acceptance
  • Acceptance other scientists did not accept it at first, but over time developed it further.
Bohr
  • Bohr in 1913 Niels Bohr discovered that electrons move in fixed orbits, explaining why atoms do not collapse.
    • (shells or energy levels)
Collaboration
  • Marie Curie and Rutherford organised a conference in 1913 for scientists to discuss models of atoms.
Scientists involved
  • Dalton, Thomson, Rutherford, Bohr, Chadwick and Geiger/Marsden each built on earlier work.
  • Evidence that does not fit a model must be taken seriously, and sharing results lets others check them.

Key terms

TermMeaning
Alpha particlea positively charged particle from radioactive decay.
Nucleusthe small, dense, positive centre of an atom.
Nuclear modelan atom with a central nucleus and electrons outside it.
Deflectiona change of direction.
Evidencedata that supports or disproves a model.
Predictiona statement of what you expect to happen if an idea is correct.

Avoid these mistakes

1
Saying the alpha particles were negative — they are positively charged.
2
Saying the nucleus is large — it is tiny compared with the atom.
3
Saying the electrons were found in this experiment — electrons were discovered earlier by Thomson.
4
Thinking the experiment supported the plum pudding model — it disproved it.

Last updated: