Alloy

What is Alloy?

A mixture of a metal with one or more other elements. The components keep their own identities and there is no fixed formula, because no chemical reaction has taken place; metallic bonding still holds the structure together, which is why an alloy is still a metal in its behaviour.

This definition is part of the Metals chapter in Cambridge O Level Chemistry.

Concepts related to Alloy

• Mixture
• brass
• Stainless Steel

Common mistakes with Alloy

• 3. “An alloy is a compound of two metals.” Repair An alloy is a mixture of a metal with other elements. There is no fixed formula, no chemical reaction has happened, and the metallic bonding is still there. Also note “other elements”, not “other metals” — carbon in steel is not a metal. Where Lesson 9.3A.
• 4. “An alloy is a compound formed when two metals are melted together.” Defect Calls a mixture a compound. Reason No reaction occurs; there is no fixed formula, and the proportions can be varied while it remains the same alloy. Repair “An alloy is a mixture of a metal with other elements.” Transfer Give one piece of evidence that brass is a mixture. Its composition can be varied; the copper and zinc are not chemically bonded.
• 5. “An alloy is a mixture of two metals.” Defect Too narrow — and it makes stainless steel impossible to describe. Reason Carbon in stainless steel is a non-metal, and it is still part of the alloy. Repair “A mixture of a metal with one or more other elements.” Transfer Name the elements in stainless steel. Iron, with chromium, nickel and carbon.
• 6. “Alloys are harder because the smaller atoms fill the gaps between the big ones.” Defect Invents a mechanism the syllabus does not use, and it is not what the diagram shows. Reason The credited mechanism is about layers, not gaps: differently sized particles disrupt the regular layers. Repair “Different-sized particles disrupt the regular layers, so the layers cannot slide over each other easily.” Transfer Does an alloy have to contain smaller particles? No — larger ones disrupt the layers just as well.
• 7. “This diagram shows an alloy because the circles are two different colours.” Defect Uses a drawing convention as physical evidence. Reason Colour is chosen by whoever drew the diagram. Size, or a key naming a second element, is what tells you. Repair “The particles are of different sizes, so this is an alloy.” Transfer A diagram has equal circles in two shades, no key. What can you conclude? Nothing about alloying — the evidence does not support a conclusion either way.