The table below gives three measured atomic properties for an unidentified element X…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
The table below gives three measured atomic properties for an unidentified element X and for several reference elements. All values correspond to isolated gaseous atoms.
┌───────────────┬────────────────┬────────────────────────┬─────────────────────┐
│ Element │ Atomic radius / pm │ Electron affinity / kJ·mol⁻¹ │ Pauling EN │
├───────────────┼────────────────┼────────────────────────┼─────────────────────┤
│ Na │ 186 │ –53 │ 0.93 │
│ Al │ 118 │ –44 │ 1.61 │
│ Si │ 111 │ –134 │ 1.90 │
│ X │ 98 │ –72 │ 2.19 │
│ S │ 88 │ –200 │ 2.58 │
│ Cl │ 79 │ –349 │ 3.16 │
└───────────────┴────────────────┴────────────────────────┴─────────────────────┘
Answer the following questions about element X.
(a) Using the data in the table, determine the period number in which element X is located. Justify your answer by referencing at least two properties.
(b) Determine the group number of element X and identify the element by name.
(c) Explain, in terms of effective nuclear charge and shielding, why the electron affinity of X is less exothermic than that of S even though both elements lie in the same period.
(d) Element X forms two common chlorides, XCl₃ and XCl₅. Predict which chloride exhibits the greater lattice energy and justify your choice using periodic trends and ionic charge considerations.