1. 1
   Iron (Z = 26) and copper (Z = 29) are both used in the catalysts of industrial processes. In many of its compounds iron is present as the Fe³⁺ ion, and copper metal is used in electrical wiring.

   (a)

   What is the condensed ground-state electron configuration of Fe³⁺?

   [1 mark]

   • A[Ar]3d⁵
   • B[Ar]4s²3d³
   • C[Ar]3d⁶
   • D[Ar]4s¹3d⁴

   (b)

   How many unpaired electrons does a ground-state Fe³⁺ ion have?

   [1 mark]

   • A1
   • B3
   • C4
   • D5

   (c)

   Deduce the full electron configuration of a copper atom and explain why it does not follow the pattern predicted by the Aufbau principle.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   When an electric discharge is passed through hydrogen gas at low pressure, the gas glows. The emitted light is analysed and found to contain three separate series of lines: one in the ultraviolet, one in the visible region and one in the infrared. Within each series the lines get closer together towards one end.

   (a)

   Which electron transition produces a line in the visible series?

   [1 mark]

   • An = 2 → n = 1
   • Bn = 4 → n = 2
   • Cn = 5 → n = 3
   • Dn = 1 → n = 3

   (b)

   Which statement correctly describes the lines within one series?

   [1 mark]

   • AThey converge at lower frequency because energy levels get further apart at high n
   • BThey are equally spaced because energy levels are equally spaced
   • CThey converge at higher frequency because energy levels get closer together at high n
   • DThey converge at longer wavelength because higher levels hold more electrons

   (c)

   Explain why hydrogen produces a line spectrum rather than a continuous spectrum, and what this shows about the electron in a hydrogen atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student uses a hand-held spectroscope to look at three light sources. A filament bulb produces a band of colour from red through to violet with no gaps. A sodium street lamp produces only two very close yellow lines, at 589.0 nm and 589.6 nm, on a dark background. A neon sign produces several lines, the brightest being a red line at 640 nm, and a mercury lamp produces a bright violet line at 436 nm among others.

   (a)

   Distinguish between the spectra of the filament bulb and the sodium lamp, and explain why the sodium lamp produces the type of spectrum it does.

   [3 marks]

   (b)

   Compare the photons in the neon red line and the mercury violet line in terms of frequency and energy. Determine how many times greater the frequency of one is than the other, and deduce what this shows about the energy levels involved.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student's homework gives the following ground-state electron configurations. Nitrogen: 1s²2s²2p³, with the three 2p electrons described as two paired in one 2p orbital and one in a second 2p orbital. Chromium: [Ar]4s²3d⁴. Sulfide ion, S²⁻: [Ne]3s²3p⁶. Zinc ion, Zn²⁺: [Ar]4s²3d⁸. The teacher also asks the student to explain how the third main energy level is organised.

   (a)

   Evaluate each of the student's answers, correcting any errors and naming the principle or exception involved.

   [6 marks]

   (b)

   Explain, with reference to sublevels and orbitals, why the third main energy level can hold 18 electrons, yet argon (Z = 18) has only 8 electrons in this level and the next element, potassium, places its outer electron in 4s. Describe the shapes of the orbitals that are occupied in the third level of argon.

   [6 marks]

   Total for question 4: 12 marks

End of questions