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Question 21M.2.SL.TZ2.4

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Date May 2021 Marks available [Maximum mark: 7] Reference code 21M.2.SL.TZ2.4
Level SL Paper 2 Time zone TZ2
Command term Draw, Explain, Write down Question number 4 Adapted from N/A
4.
[Maximum mark: 7]
21M.2.SL.TZ2.4

During electron capture, an atomic electron is captured by a proton in the nucleus. The stable nuclide thallium-205 (Tl81205) can be formed when an unstable lead (Pb) nuclide captures an electron.

(a)

Write down the equation to represent this decay.

[2]

Markscheme

Pb82205 ✓

e  -10AND  νe00 ✓

 

(b)

The neutron number N and the proton number Z are not equal for the nuclide Tl81205. Explain, with reference to the forces acting within the nucleus, the reason for this.

[2]

Markscheme

Reference to proton repulsion OR nucleon attraction ✓

strong force is short range OR electrostatic/electromagnetic force is long range ✓

more neutrons «than protons» needed «to hold nucleus together»  ✓

(c)

Thallium-205 (Tl81205) can also form from successive alpha (α) and beta-minus (β−) decays of an unstable nuclide. The decays follow the sequence α β− β− α. The diagram shows the position of Tl81205 on a chart of neutron number against proton number.

Draw four arrows to show the sequence of changes to N and Z that occur as the Tl81205 forms from the unstable nuclide.

[3]

Markscheme

any α change correct ✓

any β change correct ✓

diagram fully correct ✓


Award [2] max for a correct diagram without arrows drawn.

For MP1 accept a (−2, −2 ) line with direction indicated, drawn at any position in the graph.

For MP2 accept a (1, −1) line with direction indicated, drawn at any position in the graph.

Award [1] max for a correct diagram

 

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