3.1.1 A nuclear atom

[QB]Questions

1 Use a periodic table to pick five elements at random. List them using standard symbols and then explain how many protons and neutrons each one has.

2 Suggest why it has taken so long for scientists to develop the current model of the atom.

3 Give two strengths and two weaknesses of the analogy that an atom is like a mini solar system.

4 Draw a flowchart which shows the stages of scientific discovery which slowly broke down our idea of an atom from a solid sphere to the current quantum mechanical model.

[EXT]5 Chadwick suggested that alpha particles colliding with beryllium produced neutrons according to:

[stack subscripts and superscripts]42 + ABBe → 12

6C + 10n

What numbers are represented by A and B?

[EXT]6 A 4#MeV neutron collides head-on with a stationary hydrogen nucleus, and its kinetic energy is reduced to 1#MeV. What is the mass of the neutron?Mass of a proton = 1.6726 <mult> 1027#kg. (Hint: Remember Ek = p2/2m.)[/QB]

[ST] Answers

1) students’ own answers2) As the atom is so small, it has not been possible to image its structure. So indirect evidence has been used to infer the atomic structure.3)Strengths: The largest mass is at the centre; electrons do orbit the nucleus at varying distancesWeaknesses: electron orbits are not all in the same plane; electrons orbit proportionately ten times further away than Pluto’s orbit; electron’s location in its orbit at any given moment cannot be predicted;4) Democritus/Dalton’s solid sphere (electron discovered) Thomson’s plum pudding model (alpha scattering experiments) Rutherford’s nuclear atom Bohr’s electron energy levels model (quantum mechanics developed) Heisenberg’s quantum mechanical model5) A = 9; B = 46) mass of neutrons = mass of proton = 1.672 x 10-27 kg