Thomsons and Rutherfords Models - UNSOLVED PRACTICE SET

Q7. Draw a labelled diagram of Thomson's plum pudding model of the atom. What were its main features?

Q8. Describe Rutherford's gold foil experiment with a labelled diagram. What observations were made? 

Q9. What conclusions did Rutherford draw from his alpha particle scattering experiment?

Q10. Why did Rutherford's model fail to explain the stability of the atom?

Q11. Your school has a large playground with a tiny pebble at the centre. If you throw hundreds of cricket balls at it from a distance, most miss the pebble entirely, a few hit it and bounce back at odd angles, and some pass very close and get deflected slightly. How is this exactly analogous to Rutherford's gold foil experiment? Identify what the cricket balls, the pebble, and the empty ground represent. 

Q12. Compare Thomson's model and Rutherford's model on the basis of:

(a) Distribution of positive charge

(b) Position of electrons

Q13. Describe Thomson's plum pudding model of the atom. What experimental evidence supported it? How did Rutherford's gold foil experiment contradict this model? Explain the observations and conclusions of Rutherford's experiment in detail. 

Q14. Explain Rutherford's nuclear model of the atom. What were its merits and limitations? Why could this model not explain:

(a) The stability of the atom

(b) The line spectrum of hydrogen

How did these limitations pave the way for Bohr's model?

Q15. Imagine you are Ernest Rutherford presenting your gold foil experiment results to the Royal Society in 1911.

(a) You expected all alpha particles to pass straight through. Why? What prevailing model influenced this expectation?

(b) When some alpha particles bounced back, what did this tell you about the size and nature of the atomic nucleus?

(c) A critic asks: "If electrons are revolving around the nucleus, why don't they spiral into it due to electrostatic attraction?" How would Rutherford have responded, and why was this a valid criticism?

(d) How did the nuclear model change our understanding of atomic structure compared to Dalton's indivisible atom?

Q16. In Rutherford's experiment, alpha particles (mass = 6.64 × 10⁻²⁷ kg, charge = +3.2 × 10⁻¹⁹ C) were fired at a gold foil with a speed of 2 × 10⁷ m/s.

(a) Calculate the kinetic energy of one alpha particle in joules.

(b) If 1 in 20,000 alpha particles was deflected by more than 90°, and 10⁸ alpha particles were fired, how many bounced back?

(c) What does this extremely small fraction tell you about the relative size of the nucleus compared to the atom?

(Use KE = ½mv²)

Q17. The radius of a typical atom is approximately 10⁻¹⁰ m, while the radius of its nucleus is approximately 10⁻¹⁵ m.

(a) Calculate the ratio of the atomic radius to the nuclear radius.

(b) If the atom were scaled up to the size of a cricket stadium (radius 100 m), what would be the radius of the nucleus in this scaled model? Give your answer in millimetres.

(c) What does this comparison tell you about how much of an atom is actually empty space?

Q18. In a simulated Rutherford scattering experiment, a student fires 5000 alpha particles at a thin metal foil. The results are:

4750 particles pass straight through

200 particles are deflected by small angles

45 particles are deflected by large angles

5 particles bounce back

(a) What percentage of particles show no deflection?

(b) What percentage show significant deflection or bouncing back?

(c) Based on these percentages, estimate the ratio of the nuclear cross-sectional area to the atomic cross-sectional area.

(d) Why do you think gold was chosen for this experiment rather than aluminium or iron?