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CHEMISTRY, M1 EQ-Bank 10 MC

Element \(\ce{Y}\) forms the following ionic compound:

What is the correct spdf notation for \(\ce{Y}\) in this compound?

  1. \(1s^2\,2s^2\,2p^6\)
  2. \(1s^2\,2s^2\,2p^6\,3s^2\)
  3. \(1s^2\,2s^2\,2p^6\,3s^2\,3p^1\)
  4. \(1s^2\,2s^2\,2p^6\,3s^2\,3p^2\)
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\(A\)

Show Worked Solution
  • In \(\ce{YCl2}\), each chlorine becomes \(\ce{Cl-}\), therefore \(\ce{Y}\) must form a \(\ce{Y^2+}\).
  • The neutral atom that forms a 2+ ion is typically in group 2 (the alkaline earth metals), which have a valence configuration of \(ns^2\).
  • The neutral atom’s configuration is \(1s^2\,2s^2\,2p^6\,3s^2\). When it loses two eelctrons to form \(\ce{Y^2+}\), those are removed from the outer \(3s\) shell leaving:  \(\ce{Y^2+}: 1s^2\,2s^2\,2p^6\)

\(\Rightarrow A\)

CHEMISTRY, M1 EQ-Bank 9 MC

A radioisotope \(X\) undergoes alpha decay to form isotope \(Y\).

Isotope \(Y\) then undergoes beta decay to form lead-210.

Which of the following identifies isotope \(X\)?

  1. bismuth-214
  2. polonium-214
  3. radon-222
  4. uranium-238
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\(A\)

Show Worked Solution
  • The final product is \(\ce{^210_82Pb}\)
  • Before the beta decay, isotope \(Y\) must have the same mass number and an atomic number of 81 as during beta decay a neutron is converted into a proton.
  •     \(\ce{^210_81Tl -> ^210_82Pb + ^0_-1e^-}\)
  • Before the alpha decay, isotope \(X\) must have a mass number of \(214\) and an atomic number of \(83\) as during alpha decay the decaying particle shoots out a \(\ce{^4_2\alpha}\) particle.
  •     \(\ce{^214_83Bi -> ^210_81Tl + ^4_2\alpha}\)

\(\Rightarrow A\)

CHEMISTRY, M1 EQ-Bank 5

  1. Rank the penetrating ability of alpha, beta, and gamma radiation from lowest to highest.   (1 mark)
  1. Write a nuclear equation to show the \(\alpha\)-decay of \(\ce{^222_86Rn}\).   (1 mark)
  1. Write a nuclear equation to show the \(\beta\)-decay of \(\ce{^210_82Pb}\).   (1 mark)
  1. Explain why the radioactive decay stops when \(\ce{^206_82Pb}\) is formed.   (2 marks)
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a.    \(\alpha < \beta < \gamma\)

  • Alpha is stopped by paper, beta by aluminium, gamma requires lead/concrete.
     

b.    \(\ce{^222_86Rn -> ^218_84Po + ^4_2He}\)
 

c.    \(\ce{^210_82Pb -> ^210_83Bi + ^0_-1e^-}\)
 

d.    \(\ce{^206_82Pb}\) is a stable isotope.

  • It has the correct proton-to-neutron ratio, so the nucleus no longer needs to emit radiation to become more stable.

  • Therefore, the decay chain ends once \(\ce{^206Pb}\) is formed.

Show Worked Solution

a.    \(\alpha < \beta < \gamma\)

  • Alpha is stopped by paper, beta by aluminium, gamma requires lead/concrete.
     

b.    \(\ce{^222_86Rn -> ^218_84Po + ^4_2He}\)
 

c.    \(\ce{^210_82Pb -> ^210_83Bi + ^0_-1e^-}\)
 

d.    \(\ce{^206_82Pb}\) is a stable isotope.

  • It has the correct proton-to-neutron ratio, so the nucleus no longer needs to emit radiation to become more stable.

  • Therefore, the decay chain ends once \(\ce{^206Pb}\) is formed.

CHEMISTRY, M1 EQ-Bank 6 MC

Radon-222 has a half-life of 3.8 days. How long will it take for a 64.0 g sample to decay to 4.00 g?

  1. 7.6 days
  2. 11.4 days
  3. 15.2 days
  4. 26.6 days
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\(C\)

Show Worked Solution
  • When the sample of Radon-222 has decayed to \(4.00\ \text{g}\) there is \(\dfrac{4.00}{64.0} = \dfrac{1}{16}\) left of the original sample.
  • As \(\dfrac{1}{16} = \left(\dfrac{1}{2}\right)^4\), the sample has had 4 half-lives pass.
  • Hence \(4 \times 3.8 = 15.2\ \text{days}\) have passed.

\(\Rightarrow C\)

CHEMISTRY, M1 EQ-Bank 4 MC

Which of the following pairs represents isotopes of the same element?

  1. \(\ce{^12_6C}\) and \(\ce{^13_6C}\)
  2. \(\ce{^14_6C}\) and \(\ce{^14_7N}\)
  3. \(\ce{^23_11Na}\) and \(\ce{^24_12Mg}\)
  4. \(\ce{^35_17C}\) and \(\ce{^35_18Ar}\)
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\(A\)

Show Worked Solution
  • Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons.
  • Option A: Both are carbon and so have 6 protons but differ in the number of neutrons they have hence leading to different mass numbers.

\(\Rightarrow A\)

CHEMISTRY, M1 EQ-Bank 4

Compare and contrast two isotopes of hydrogen.   (2 marks)

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  • Two of hydrogens isotopes are hydrogen-1 (protium) and hydrogen-2 (deuterium).
  • The atoms have the same number of protons but a different number of neutrons in the nucleus. Hydrogen-1 has 1 proton and 0 neutrons, while hydrogen-2 has 1 proton and 1 neutron.
Show Worked Solution
  • Two of hydrogens isotopes are hydrogen-1 (protium) and hydrogen-2 (deuterium).
  • The atoms have the same number of protons but a different number of neutrons in the nucleus. Hydrogen-1 has 1 proton and 0 neutrons, while hydrogen-2 has 1 proton and 1 neutron.

CHEMISTRY, M1 EQ-Bank 3 MC

Thorium-232 undergoes a sequence of radioactive decays. In the first part of this sequence, what is the isotope produced when thorium-232 undergoes one alpha decay followed by one beta decay?

  1. \(\ce{^228_88Ra}\)
  2. \(\ce{^228_89Ac}\)
  3. \(\ce{^232_90Th}\)
  4. \(\ce{^228_90Th}\)
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\(B\)

Show Worked Solution
  • During Alpha decay, the radio active particle emits a alpha particle \(\ce{^4_2He}\).
  •    \(\ce{^232_90Th -> ^228_88Ra + ^4_2He}\)
  • Beta decay process involves a neutron being converted to a proton with the emission of an electron.
  •    \(\ce{^228_88Ra -> ^228_89Ac + ^0_-1e^-}\)

\(\Rightarrow B\)

CHEMISTRY, M1 EQ-Bank 3

Thorium exists in several isotopic forms. The existence of these isotopes can be shown by placing a thorium sample in a mass spectrometer, in which atoms are vaporised, electrically charged, and the ratio of the mass/charge for each is compared.

A mass spectrogram of thorium is shown below. The mass number is displayed on the x-axis and the % abundance on the y-axis.
 

  1. What is the \(Z\) for thorium?   (1 mark)
  1. Write the three isotopes of thorium.   (1 mark)
  1. Using the mass spectrogram, calculate the relative atomic weight of natural thorium. Show your working.   (2 marks)
  1. Thorium-232 decays to radium-228. Write the nuclear equation to show the radioactive decay of thorium-232.   (2 marks)
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a.    \(Z=90\)

b.    \(\ce{^228_90Th, ^230_90Th, ^232_90Th}\).

c.    \(232.0\)

d.    \(\ce{^232_90Th -> ^228_88Ra + ^4_2He}\)

Show Worked Solution

a.    \(Z = 90\) (atomic number)
 

b.    \(\ce{^228_90Th, ^230_90Th, ^232_90Th}\).
 

c.     \(M\) \(=\dfrac{(228 \times 0.02) + (230 \times 0.8) + (232 \times 99.18)}{100}\)
    \(=231.98\)
    \(=232.0\ \text{(4 sig.fig)}\)

 

d.    Thorium-232 undergoes alpha decay:

\(\ce{^232_90Th -> ^228_88Ra + ^4_2He}\)

CHEMISTRY, M1 EQ-Bank 1

The element tellurium is a brittle, silver-grey metalloid used in solar panels and thermoelectric devices.

  1. Tellurium has two naturally occurring stable isotopes that contribute to its average atomic mass. One of these isotopes, \(\ce{^126Te}\), has a percentage abundance of 45.2%. Calculate the mass number of the other isotope.   (2 marks)
  1. One unstable isotope of tellurium is \(\ce{^130Te}\). Write a nuclear equation for the decay of this isotope when it undergoes beta decay.   (1 marks)
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a.    \(\ce{^129Te}\)

b.    \(\ce{^130_52Te -> ^130_53I + ^0_-1e}\)

Show Worked Solution

a.    Let the mass number of the other isotope of Tellurium be \(x\). Therefore:

\((0.452 \times 126) + (0.548x)\)  \(=127.6\)  
\(0.548x\) \(=70.648\)  
\(x\) \(=128.9 \approx 129\)  
     
  • The mass number of the other stable isotope of Tellurium is 129.

b.    \(\ce{^130_52Te -> ^130_53I + ^0_-1e}\)

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`

Show Worked Solution
  • 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).
Show Worked Solution
  • 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`

Show Worked Solution
  • 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`