- Thallium is a heavy metal in group 13 of the periodic table.
(a) 30 % of thallium atoms contain 122 neutrons and the remainder 124 neutrons.
(i) Deduce the nuclear symbol of the isotope of thallium containing 122 neutrons. Use section 7 of the data booklet. [1]
(ii) Calculate, to two decimal places, the relative atomic mass of thallium. [2]
(b) Thallium(I) sulfate has the formula Tl₂SO₄.
(i) The compound contains both ionic and covalent bonds. State which particles are joined by covalent bonds and which are joined by ionic bonds. [2]
(ii) Contrast covalent and ionic bonds based on the valence electron interactions. [1]
(iii) State the enthalpy term that characterises the strength of the bonding between the ions in an ionic solid. [1]
(iv) Write an equation for producing thallium(I) sulfate solution by reacting solid thallium(I) hydroxide with sulphuric acid. [2]
(v) Calculate the volume of 2.00 mol dm⁻³ sulphuric acid required to react completely with 10.0 g of thallium(I) hydroxide. [3]
(vi) Predict whether or not thallium(I) hydroxide is amphoteric, considering the position of thallium in the periodic table. [1]
(vii) Discuss how the relative reactivity of copper and thallium could be established using the metals and aqueous solutions of their sulfates. [2]
(viii) Discuss the products at the electrodes when aqueous thallium(I) sulfate is electrolysed. Use standard reduction potential of Tl⁺(aq) + e⁻ ⇌ Tl(s) = –0.34 V and section 19 of the data booklet. [2]
(c) Thallium has an atomic emission spectrum with a strong green line.
(i) State the feature of the atomic emission spectrum that may be used to find the ionisation energy of the element. [1]
(ii) Calculate the wavelength that corresponds to the ionisation energy of thallium. Use sections 1, 2 and 9 of the data booklet. [3]
(iii) Explain why, in terms of nuclear charge and the shielding of the valence electrons, the first ionisation energy of thallium is lower than that of lead. [2]