9.2. Periodicity of chemical properties of the elements in Period 3
A subsection of Chemistry, 9701, through 9. The Periodic Table: chemical periodicity
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This question is about Period 3 elements and their compounds. Give an explanation for each of the following statements. The atomic radius decreases across Period 3 (Na to Ar). The first ionisation energy of sulfur is lower than that of phosphorus. Sodium is a better electrical conductor than phosphorus. Magnesium is a better electrical conductor than sodium. The flow chart below shows a series of reactions. Awhite precipitate, EB+ CD+ MgHNO3reagent Xheat MgO+ H2O+ Give the formula of each of the compounds A to D. A B C D E reacts with dilute aqueous acid to produce a gas that turns limewater cloudy. Suggest the identity of reagent X.
9701_m16_qp_22
THEORY
2016
Paper 2, Variant 2
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Two elements, V and W, are in adjacent groups in the Periodic Table. V reacts with oxygen to form an acidic gas, X. V forms an anion with formula VOm –. W reacts with oxygen to form an acidic gas, Y. W forms an anion with formula WOn 2–. A solution of WOn 2– forms a white precipitate with Ba2+but shows no visible reaction with Mg2+. Complete the table below. identity or value V X m W Y n By referring to enthalpy changes, explain why WOn 2– forms a white precipitate with Ba2+but shows no visible reaction with Mg2+.
9701_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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The table shows information about some of the elements in the third period. element Na Mg Al P S Cl atomic radius / nm 0.186 0.160 0.143 0.110 0.104 0.099 radius of most common ion / nm 0.095 0.065 0.050 0.212 0.184 0.181 maximum oxidation number of the element in its compounds +1 +7 Complete the table to show the maximum oxidation number of each element in its compounds. Explain why the atomic radius of elements in the third period decreases from Na to Cl. The radius of the most common ion of Mg is much smaller than the radius of the most common ion of S. Identify both ions and explain the difference in their radii. Phosphorus is a non-metal in the third period. It reacts vigorously with excess oxygen but slowly with chlorine. Some reactions of phosphorus are shown. phosphorus Aexcess O2reaction 1 Cl 2reaction 2 PCl 5+ HCl Bwater Write an equation to represent reaction 1, the formation of compound A. Give two observations you could make in reaction 2. 1. 2. Name compound B. Cerium is a lanthanoid metal that shows similar chemical reactions to some elements in the third period. Most of cerium’s compounds contain Ce3+ or Ce4+ ions. Cerium shows the same structure and bonding as a typical metal. Draw a labelled diagram to show the structure and bonding in cerium. Cerium(oxide, CeO2, is a ceramic. Suggest two physical properties of cerium(oxide. 1. 2. A naturally occurring sample of cerium contains only four isotopes. Data for three of the isotopes are shown in the table. isotope 136Ce 138Ce 140Ce 142Ce relative isotopic mass 135.907 137.906 139.905 to be calculated percentage abundance 0.185 0.251 88.450 to be calculated The Ar of the sample is 140.116. Use these data to calculate the relative isotopic mass of the fourth isotope in this sample of cerium. Give your answer to three decimal places. relative isotopic mass =
9701_m17_qp_22
THEORY
2017
Paper 2, Variant 2
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The mass spectrum of silicon is shown. 1.0 0.5 0.047 0.031 0.922 m / e relative intensity Calculate the Ar of silicon. Give your answer to two decimal places. Ar = Silicon forms a low boiling point chloride which reacts with water. Write an equation to show the reaction of the chloride with water. Draw a three-dimensional diagram showing the shape of the chloride. Give the Cl – Si – Cl bond angle. Silicon reacts with oxygen to form a high melting point oxide. ● Suggest the formula of the oxide. ● Suggest, in terms of structure, why the oxide has a high melting point whereas the chloride has a low boiling point. Element A is in the same period as silicon. Element A reacts with dilute nitric acid to form a nitrate. This nitrate decomposes on heating to form an oxide. Write an equation for the decomposition of the nitrate. The oxide of element A has a high melting point. Suggest the structure and bonding present in the oxide of A.
9701_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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