IGCSE Chemistry 0620: Classifying Elements from Their Properties

A materials science teacher gives the class four unlabelled element samples, W, X, Y and Z, each with a short property card, and asks the class to identify which part of the Periodic Table each element belongs to.

W: density $8.9\ \text{g/cm}^3$ , melting point $1455\,^{\circ}\text{C}$ ; forms green and blue compounds; used as a catalyst in some industrial reactions.
X: a soft metal with a low density; reacts vigorously with cold water, forming an alkaline solution and floating on the surface as it reacts.
Y: a colourless gas that exists as single, separate atoms; does not react with other substances.
Z: a diatomic non-metal that is a dark grey-black solid at room temperature; reacts with iron wool when gently heated.

(a) State which element, W, X, Y or Z, is a transition element. Give one reason for your answer. [2]

(b) State which element is a Group I (alkali) metal. Give one reason for your answer. [2]

(d) State which element is a noble gas. Give one reason for your answer. [2]

Part (a): Identifying the transition element

Transition elements are metals with high density, high melting points, that form coloured compounds, and are often used as catalysts.

Element W has a high density ( $8.9\ \text{g/cm}^3$ ), a high melting point ( $1455\,^{\circ}\text{C}$ ), forms green and blue compounds, and is used as a catalyst, matching every one of these transition element properties.

W is the transition element.

Part (b): Identifying the Group I metal

The Group I alkali metals are soft, have low density, and react vigorously with cold water, forming an alkaline solution and often floating on the water’s surface as they react.

Element X is described as a soft, low-density metal that reacts vigorously with cold water, forms an alkaline solution, and floats while reacting, this matches the Group I pattern exactly.

X is the Group I metal.

Part (c): Identifying the Group VII element

The Group VII halogens are diatomic non-metals. Their appearances at room temperature range from a pale yellow-green gas (chlorine), to a red-brown liquid (bromine), to a grey-black solid (iodine). Halogens are also known to react with hot iron wool, forming iron halides.

Element Z is a diatomic non-metal, a dark grey-black solid, and reacts with iron wool on heating, this matches the appearance and reactivity of a halogen (specifically, matching iodine’s known appearance).

Z is the Group VII (halogen) element.

Part (d): Identifying the noble gas

The Group VIII noble gases are unreactive, monatomic gases, they exist as single, separate atoms rather than molecules, because their outer shells are already full.

Element Y is a colourless gas made of single atoms that does not react with other substances, this matches the noble gas description exactly.

Y is the noble gas.

Final answers

(a) W is the transition element (high density, high melting point, coloured compounds, catalyst).
(b) X is the Group I metal (soft, low density, reacts vigorously with cold water, alkaline solution).
(c) Z is the Group VII element (diatomic non-metal, grey-black solid, reacts with hot iron wool).
(d) Y is the noble gas (unreactive, monatomic gas).