Periodicity: Question 9

Worked solution

Step 1: Interpret the clues about J’s chloride

J’s chloride is described as a colourless, volatile liquid at room temperature that hydrolyses immediately and vigorously, giving off steamy HCl fumes and leaving a strongly acidic solution.

A volatile liquid held together only by weak intermolecular forces (not a giant lattice) must have a simple molecular structure. Vigorous hydrolysis producing HCl fumes matches the behaviour already established for covalent, non-metal chlorides such as $\text{SiCl}_4$. By contrast, the purely ionic chlorides of the metals (Na, Mg) either do not hydrolyse at all (NaCl) or hydrolyse only very slightly ($\text{MgCl}_2$), and neither produces visible fuming.

Step 2: Apply the Period 3 oxide trend

Across Period 3, oxides shift from strongly basic (Na, Mg) through amphoteric (Al) to acidic (Si, P, S). Elements whose chlorides are simple molecular and hydrolyse vigorously lie on the non-metallic, right-hand side of the period, and their oxides in this region are acidic (e.g. $\text{SiO}_2$, $\text{P}_4\text{O}_{10}$, $\text{SO}_3$). This makes option B correct: J is a non-metal with a simple molecular structure, and its oxide is likely to be acidic.

Why the other options are wrong

• A: A reactive metal’s chloride (like NaCl or $\text{MgCl}_2$) is an ionic solid that either does not hydrolyse or hydrolyses only very slightly. It would not be a volatile liquid that fumes and hydrolyses immediately in water.
• C: A giant metallic lattice does not form a simple molecular, volatile chloride; also, ionic chlorides of reactive metals do not produce vigorous fuming hydrolysis.
• D: A giant covalent lattice (like silicon’s oxide) has an extremely high melting point and would not itself be a volatile liquid; a volatile chloride must be simple molecular, not giant covalent.

Final answer

• Element J is most likely a non-metal with a simple molecular structure, forming an acidic oxide, option B.