O Level / IGCSE Chemistry · Metals. A short explanation of the idea, the rules to remember, the mistake to avoid, a worked example and practice questions with answers.
Elements are sorted into metals and non-metals by their properties. Metals are good conductors of heat and electricity, are malleable (can be hammered into shape) and ductile (can be pulled into wires), and mostly have high melting and boiling points. Non-metals are usually poor conductors, are brittle when solid and mostly have low melting and boiling points.
Metals also share chemical reactions. Many react with dilute acids to give a salt and hydrogen. Reactive metals react with cold water to form a metal hydroxide and hydrogen; less reactive ones need steam and form a metal oxide and hydrogen. Metals react with oxygen to form metal oxides, most of which are basic.
Writing that magnesium and steam give magnesium hydroxide. With steam the product is the oxide, MgO; a hydroxide forms only when a metal reacts with cold water.
Answer: 8.0 g of magnesium oxide.
Try each one, then open the answer.
Answer: B. 2Mg + O2 → 2MgO. Mg2+ and O2− give MgO; as a metal oxide it is basic.
Answer: A. The more reactive the metal, the faster it produces hydrogen with the acid, so the shortest time is the most reactive: P (15 s), then R (60 s), then Q (240 s). S gives no gas, so it is the least reactive (below hydrogen).
Answer: C. Metals usually have high melting points, conduct electricity as solids and are malleable. The high-melting non-conductor is a giant covalent substance such as diamond.
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