IGCSE · 5 · structured
Nuclear physics · Question 8
Nuclear physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 8
- Topics
- 2
- Answer
- Complete
Carbon has two naturally occurring stable isotopes, ¹²₆C and ¹³₆C, and one radioactive isotope, ¹⁴₆C, which decays by β-emission to nitrogen.
- (a)
Define Define the term isotope.
2 marks - (b)
Explain Explain why the three isotopes of carbon all behave identically in chemical reactions.
2 marks - (c)
State Complete the decay equation for carbon-14, giving the nucleon and proton numbers of the nitrogen nucleus produced: ¹⁴₆C → ᴬ_Z N + ⁰₋₁β
2 marks - (d)
Explain A β-particle is an electron, yet there are no electrons in a nucleus. Explain where the emitted β-particle comes from.
2 marks
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(a)
Define Define the term isotope.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
atoms of the same element, with the same number of protons (same proton number)
- 2
but different numbers of neutrons (different nucleon number)
(b)
Explain Explain why the three isotopes of carbon all behave identically in chemical reactions.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
chemical behaviour is determined by the electrons, particularly the outer electrons
- 2
all three isotopes have 6 protons and therefore the same number and arrangement of electrons
(c)
State Complete the decay equation for carbon-14, giving the nucleon and proton numbers of the nitrogen nucleus produced: ¹⁴₆C → ᴬ_Z N + ⁰₋₁β
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Conservation of nucleon number gives A = 14 for the nitrogen nucleus.
- 2
Conservation of proton number gives Z = 7 for the nitrogen nucleus.
(d)
Explain A β-particle is an electron, yet there are no electrons in a nucleus. Explain where the emitted β-particle comes from.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
a neutron in the nucleus changes into a proton
- 2
and an electron is created and emitted at that moment, which is why the proton number rises by one while the nucleon number is unchanged
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