Atomic structure and the periodic tableEdexcel A-Level Chemistry: Topic test

1. 1
   Zinc, atomic number 30, is used to galvanise steel. A chemist is studying the isotope ⁶⁴Zn and its ion ⁶⁴Zn²⁺.

   (a)

   How many neutrons are there in one ⁶⁴Zn²⁺ ion?

   [1 mark]

   • A28
   • B30
   • C34
   • D64

   (b)

   Which is the electronic configuration of a ⁶⁴Zn²⁺ ion?

   [1 mark]

   • A1s²2s²2p⁶3s²3p⁶3d¹⁰
   • B1s²2s²2p⁶3s²3p⁶3d¹⁰4s²
   • C1s²2s²2p⁶3s²3p⁶3d⁸4s²
   • D1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹

   (c)

   State what is meant by relative atomic mass.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Bromine consists of two isotopes, ⁷⁹Br and ⁸¹Br, which occur in approximately equal abundance. Bromine vapour, Br₂, is analysed in a mass spectrometer and every ion formed carries a single positive charge.

   (a)

   What is the highest m/z value of a molecular ion in the mass spectrum of bromine vapour?

   [1 mark]

   • A158
   • B160
   • C162
   • D81

   (b)

   What are the relative heights of the three molecular ion peaks, in order of increasing m/z?

   [1 mark]

   • A1 : 1 : 1
   • B1 : 1
   • C1 : 3 : 1
   • D1 : 2 : 1

   (c)

   Explain why the molecular ion peak at m/z 160 is twice as tall as the peak at m/z 158.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The first five successive ionisation energies of calcium, in kJ mol⁻¹, are: 1st 590, 2nd 1145, 3rd 4912, 4th 6491 and 5th 8153.

   (a)

   Write an equation, including state symbols, for the second ionisation energy of calcium. Explain why the second ionisation energy of calcium is greater than the first.

   [3 marks]

   (b)

   Explain how the data show that calcium is in Group 2 and provide evidence for the existence of electron shells. Give the electronic configuration of a Ca²⁺ ion in 1s notation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The melting temperatures of the Period 2 elements are: lithium 181 °C, beryllium 1287 °C, boron 2076 °C, carbon (as diamond) about 3550 °C, nitrogen −210 °C, oxygen −219 °C, fluorine −220 °C and neon −249 °C.

   (a)

   Explain the trend in melting temperature across Period 2 from lithium to neon, in terms of structure and bonding.

   [6 marks]

   (b)

   Describe the arrangement of electrons in the 2s and 2p sub-shells of a carbon atom and of an oxygen atom in electrons-in-boxes notation. Explain how the electronic configuration of each element is linked to the structure it forms and to its melting temperature.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Neon (atomic number 10) has three naturally occurring isotopes: ²⁰Ne (90.5%), ²¹Ne (0.3%) and ²²Ne (9.2%).

   (a)

   What is the relative atomic mass of neon, to three significant figures?

   [1 mark]

   • A20.0
   • B20.2
   • C21.0
   • D22.0

   (b)

   How many neutrons are there in one atom of ²²Ne?

   [1 mark]

   • A22
   • B10
   • C32
   • D12

   (c)

   A second sample of neon has been enriched so that it contains only ²⁰Ne and ²²Ne. Its relative atomic mass is 20.4. Calculate the percentage of ²²Ne in this sample.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   The first ionisation energies of four Group 2 elements, in kJ mol⁻¹, are: beryllium 900, magnesium 738, calcium 590 and strontium 550.

   (a)

   Which statement best explains why the first ionisation energy decreases down Group 2?

   [1 mark]

   • AThe outer electron is further from the nucleus and more shielded, and this outweighs the increased nuclear charge
   • BThe nuclear charge of the atoms decreases down the group
   • CThe number of electrons in the outer shell increases down the group
   • DThe outer electron is removed from a p sub-shell in the lower elements

   (b)

   Which equation represents the first ionisation energy of beryllium?

   [1 mark]

   • ABe(g) → Be²⁺(g) + 2e⁻
   • BBe(g) → Be⁺(g) + e⁻
   • CBe(s) → Be⁺(g) + e⁻
   • DBe⁺(g) → Be²⁺(g) + e⁻

   (c)

   Write the electronic configuration of a calcium atom (atomic number 20) in 1s notation. State the block of the periodic table to which calcium belongs.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Boron is used to absorb neutrons in nuclear reactors. Natural boron contains only two isotopes, ¹⁰B and ¹¹B, and has a relative atomic mass of 10.81.

   (a)

   Calculate the percentage abundance of ¹⁰B in natural boron.

   [3 marks]

   (b)

   Boron vapour is analysed by mass spectrometry. State the m/z values of the two peaks for B⁺ ions and predict their relative heights. Explain why the relative atomic mass of boron is not a whole number.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A teacher gives students ionisation energy data. The first six successive ionisation energies of silicon (atomic number 14), in kJ mol⁻¹, are: 786, 1577, 3232, 4356, 16091 and 19805. The first ionisation energies of neon (atomic number 10), sodium (atomic number 11) and argon (atomic number 18) are 2081, 496 and 1521 kJ mol⁻¹ respectively.

   (a)

   Explain how the successive ionisation energies of silicon provide evidence for electron shells, and why each successive ionisation energy is greater than the one before it.

   [6 marks]

   (b)

   Explain why the first ionisation energy of sodium is much lower than that of neon, and why the first ionisation energy of neon is higher than that of argon.

   [6 marks]

   Total for question 8: 12 marks

End of questions