Paper 2 Atomic Structure Answers

Q1 Rutherford Scattering

1. Most alpha particles pass through with little/no deflection; a small number are deflected through large angles or rebound. [2]
2. Passing through implies atoms are mostly empty space. Large deflections imply positive charge and most mass are concentrated in a tiny nucleus. [4]
3. Positive alpha particles experience strong electrostatic repulsion when they pass very close to the small positive nucleus. [2]

Q2 Energy Level Transition

1. Energy emitted $=(-1.51)-(-3.40)=1.89\mathrm{eV}$. [2]
2. $\lambda =1240/1.89=656\mathrm{nm}$. [2]
3. Ionisation energy from $-3.40\mathrm{eV}$ is $3.40\mathrm{eV}$. [1]

Q3 Emission and Absorption

1. Emission lines are bright lines from downward transitions in a low-pressure gas; absorption lines are dark lines in a continuous spectrum after photons are absorbed for upward transitions. [3]
2. The same pairs of energy levels are involved; emission releases $\Delta E$ while absorption requires a photon of energy $\Delta E$. [2]