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CHEMISTRY, M1 2009 HSC 1 MC

Which of the following is an important factor in predicting the nuclear stability of an isotope?

  1. Atomic radius
  2. Nuclear radius
  3. The ratio of neutrons to protons
  4. The ratio of electrons to protons
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`C`

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→ Nuclear stability refers to the stability of the nucleus within the atom. 

→ As the nucleus is made up of protons and neutrons, it is the ratio of these particles which are an important factor in predicting nuclear stability.

`=>C`

CHEMISTRY, M1 2011 HSC 23a

Element 112 was first synthesised in 1996 and officially named in 2009 as copernicium, \(\ce{Cn}\).

Explain why the transuranic isotope \( \ce{^{278 }_{112}Cn}\) is unstable.  (1 mark)

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→ Isotopes such as copernicium-278 are unstable because they are heavy nuclei with high neutron-proton ratios (eg. Cn-278 = 166 : 112).

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→ Isotopes such as copernicium-278 are unstable because they are heavy nuclei with high neutron-proton ratios (eg. Cn-278 = 166 : 112).

CHEMISTRY, M1 2011 HSC 7 MC

Which of the following lists contains ONLY unstable isotopes?

  1. \( \ce{^{207}_{82}Pb}, \ \ce{^{99}_{43}Tc}, \ \ce{^{12}_{7}N} \)
  2. \( \ce{^{214}_{82}Pb}, \ \ce{^{46}_{20}Ca}, \ \ce{^{99}_{43}Tc}\)
  3. \( \ce{^{238}_{92}U}, \ \ce {^{40}_{20}Ca}, \ \ce{^{12}_{7}N}\)
  4. \( \ce{^{238}_{92}U}, \ \ce{^{40}_{20}Ca}, \ \ce{^{99}_{43}Tc}\)
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`B`

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→ The stability of Isotopes is determined by their  Neutron:Proton Ratio and the total number of nucleons (neutrons + protons) in the nucleus.

→ Elements with an atomic number smaller than 20 (Z < 20) are stable with their  Neutron : Proton  ratio approximating 1 : 1

→ Heavier elements (Z = 20 – 83) require a higher  Neutron : Proton  ratio (usually about 1.5 : 1) to maintain nuclear stability as more neutrons are required to mitigate the inherent repulsive forces between the growing number of Protons and prevent nuclear decay.

→ This relationship can be graphed and is commonly referred to as the ‘Belt of Stability’. Elements and their isotopes with an atomic number greater than 83 are all only unstable.

`=>B`