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Solutions: Atomic Structure

Q12.

(a) State what is meant by the specific charge of a nucleus and give an appropriate unit for this quantity.

Specific charge is the ratio of charge to mass of the nucleus

The unit is C kg–1

(2 marks)

(b) Nucleus X has the same nucleon number as nucleus Y. The specific charge of X is 1.25 times greater than that of Y.

(i) Explain, in terms of protons and neutrons, why the specific charge of X is greater than that of Y.

The number of protons plus the number of neutrons is the same, therefore the mass is virtually the same for both nuclei but if X has more protons (or less neutrons) than Y is will have a greater charge and therefore the specific charge will be greater.

(2 marks)

(ii) Nucleus X is . Deduce the number of protons and the number of neutrons in nucleus Y.

Let 'm' be the mass of a proton or neutron.

Specific charge of X is 5e/10m = 0.5 e/m

Specific charge of Y is 0.5/1.25 x e/m = 0.4 e/m = 4e/10m

Therefore there are 4 protons in the nucleus and 6 neutrons.

Answer: 6 neutrons

(4 marks)

(Total 8 marks)