Atomic structureAQA A-Level Chemistry: Topic test

1. 1
   Potassium-40 is a radioactive isotope found in bananas and in the human body. Natural potassium is a mixture of the isotopes ³⁹K, ⁴⁰K and ⁴¹K. Potassium has atomic number 19.

   (a)

   How many neutrons are there in one atom of ⁴⁰K?

   [1 mark]

   • A19
   • B20
   • C21
   • D40

   (b)

   How many electrons are there in a ³⁹K⁺ ion?

   [1 mark]

   • A18
   • B19
   • C20
   • D39

   (c)

   Give the full electron configuration of a potassium atom and of a K⁺ ion, using s and p notation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A geochemist measures the isotopes of boron in a mineral using a time of flight (TOF) mass spectrometer. The boron is ionised to form 1+ ions. The spectrum has two peaks: one at m/z = 10 with relative abundance 1.0 and one at m/z = 11 with relative abundance 4.0.

   (a)

   In electron impact ionisation, how are positive ions formed from the vaporised sample?

   [1 mark]

   • AThe sample is dissolved in a solvent and each particle gains a proton
   • BThe sample is bombarded with high-energy electrons, which knock out an outer electron
   • CParticles of the sample collide with each other and transfer electrons
   • DThe sample is passed through an electric field, which strips off an electron

   (b)

   What is the relative atomic mass of boron in this sample?

   [1 mark]

   • A10.2
   • B10.5
   • C11.0
   • D10.8

   (c)

   Describe how the ions are detected in a TOF mass spectrometer and how the signal from the detector gives the relative abundance of each isotope.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The successive ionisation energies of aluminium, in kJ mol⁻¹, are: first 578, second 1817, third 2745, fourth 11 577 and fifth 14 842.

   (a)

   Write an equation, including state symbols, to represent the second ionisation energy of aluminium, and explain why the second ionisation energy is greater than the first.

   [3 marks]

   (b)

   Explain how the data show that aluminium is in Group 3, and give the full electron configuration of an aluminium atom.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Strontium is a Group 2 metal found in some rocks. A sample of strontium is analysed in a TOF mass spectrometer as 1+ ions and contains these isotopes: ⁸⁴Sr 0.6%, ⁸⁶Sr 9.9%, ⁸⁷Sr 7.0% and ⁸⁸Sr 82.5%. Strontium has atomic number 38. Its first, second and third ionisation energies are 550, 1064 and 4138 kJ mol⁻¹, and the first ionisation energy of magnesium is 738 kJ mol⁻¹.

   (a)

   Calculate the relative atomic mass of strontium in this sample, to one decimal place. State the numbers of protons, neutrons and electrons in a ⁸⁷Sr²⁺ ion.

   [6 marks]

   (b)

   Explain how the ionisation energies show that strontium is in Group 2, and explain why the first ionisation energy of strontium is lower than that of magnesium.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Iodine-131, a radioactive isotope of iodine, is used to treat an overactive thyroid gland. Stable iodine in the body is ¹²⁷I. Iodine has atomic number 53.

   (a)

   How many electrons are there in an ¹³¹I⁻ ion?

   [1 mark]

   • A52
   • B53
   • C78
   • D54

   (b)

   Which statement about atoms of ¹²⁷I and ¹³¹I is correct?

   [1 mark]

   • AThey have different numbers of protons
   • B¹³¹I atoms have four more neutrons than ¹²⁷I atoms
   • C¹³¹I atoms have four more electrons than ¹²⁷I atoms
   • DThey have different chemical properties because their masses differ

   (c)

   Define the term first ionisation energy, and write an equation, including state symbols, for the first ionisation of iodine.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Lithium is used in rechargeable batteries. A sample of lithium enriched in ⁶Li is analysed in a TOF mass spectrometer. It contains 8.0% ⁶Li and 92.0% ⁷Li, and is ionised to form 1+ ions. Lithium has atomic number 3.

   (a)

   What is the relative atomic mass of lithium in this sample?

   [1 mark]

   • A6.08
   • B6.50
   • C6.92
   • D7.00

   (b)

   What is the electron configuration of a Li⁺ ion?

   [1 mark]

   • A1s²
   • B1s² 2s¹
   • C1s² 2s²
   • D1s¹ 2s¹

   (c)

   Explain how a TOF mass spectrometer separates ⁶Li⁺ ions from ⁷Li⁺ ions after they have been accelerated.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Manganese is added to steel to make it harder. Manganese has atomic number 25 and its only stable isotope is ⁵⁵Mn.

   (a)

   Write the full electron configurations of a manganese atom and of a Mn²⁺ ion, and state which electrons are lost first when the ion forms.

   [3 marks]

   (b)

   Manganese forms the ion ⁵⁵Mn²⁺. State the numbers of protons, neutrons and electrons in this ion, and the m/z value of the peak it gives in a mass spectrum.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A teacher sets a challenge on Period 3 and argon. First ionisation energies, in kJ mol⁻¹: magnesium 738, aluminium 578, phosphorus 1012, sulfur 1000 and argon 1520. Argon in air is almost all ⁴⁰Ar, formed by the radioactive decay of ⁴⁰K, with traces of ³⁶Ar and ³⁸Ar. A sample of argon is analysed in a TOF mass spectrometer as 1+ ions and contains 0.34% ³⁶Ar, 0.06% ³⁸Ar and 99.60% ⁴⁰Ar.

   (a)

   Explain why the first ionisation energy of aluminium is lower than that of magnesium, and why the first ionisation energy of sulfur is lower than that of phosphorus.

   [6 marks]

   (b)

   Calculate the relative atomic mass of the argon sample to two decimal places. State which ion reaches the detector first and explain why. Explain why argon has the highest first ionisation energy of the elements listed.

   [6 marks]

   Total for question 8: 12 marks

End of questions