GRADE 9 Integrated Science MIXTURES,ELEMENTS AND COMPOUNDS – Metals and alloys Notes

What are metals?

Metals are elements (pure substances made of one kind of atom) that usually:

• Have a shiny surface (luster) ✨
• Conduct heat and electricity well ⚡
• Can be hammered into sheets (malleable) or pulled into wires (ductile)
• Are usually solid at room temperature (except mercury) and feel hard and heavy
• Often make a ringing sound when hit (sonorous)

Common metal examples in Kenya

Iron (Fe), Copper (Cu), Aluminium (Al), Zinc (Zn), Gold (Au) and Silver (Ag). - Iron is used for nails, beams and sheets; aluminium for roofing sheets and cooking pans; copper for electric wires.

What are alloys?

An alloy is a mixture of two or more elements, at least one of which is a metal. Most alloys are homogeneous solids where the different atoms mix together.

Examples of common alloys

• Steel — iron + small carbon (strong; used in buildings, bridges, vehicles)
• Stainless steel — iron + chromium (+ sometimes nickel) (resists rust; used in cooking pots, cutlery)
• Brass — copper + zinc (used in musical instruments, taps)
• Bronze — copper + tin (used for tools, sculptures)
• Duralumin — aluminium + copper (light and strong; used in aircraft parts)

Why use alloys instead of pure metals?

• Stronger and harder than the pure metal
• Less likely to bend or break
• Better resistance to rust and wear (e.g., stainless steel)
• Different properties (lighter, more flexible, better conductor) can be achieved

How are alloys made?

1. Melting: Heat the main metal until liquid. 🔥
2. Mixing: Add the other metal(s) and mix well so atoms spread evenly.
3. Cooling: Allow the liquid to cool and solidify into a single solid with mixed atoms.

Some modern methods: powder metallurgy (mix powdered metals and press + heat) for special alloys.

How to tell metals/alloys in a simple class test

• Shine test: Do they look shiny after scraping?
• Conductivity test: Do they light a bulb or make a circuit? (Use safe low-voltage DC) ⚡
• Magnet test: Iron and steels are magnetic; copper and aluminium are not. 🧲
• Bend test: Are they malleable or brittle? (Small, safe samples only)
• Rust test: Iron rusts (brown-orange); stainless steel resists rust. Keep safe and clean up!

Safety: Wear gloves and goggles. Do not heat metals in the classroom without teacher supervision.

Link to the topic "Mixtures, Elements and Compounds"

- Metals discussed here are elements when pure (e.g., Fe, Cu).
- Alloys are mixtures (not compounds) because components are mixed in variable amounts and do not react to form a fixed new compound.

Key terms (short)

• Element — pure substance made of one type of atom (e.g., iron).
• Alloy — mixture of metals (and sometimes non-metals) with improved properties.
• Malleable — can be hammered into thin sheets.
• Ductile — can be drawn into wires.

Quick classroom quiz (answer after trying)

1. Is brass a compound or a mixture? (Answer: mixture — an alloy)
2. Give one reason why steel is used for building instead of pure iron.
3. Which metal is a good electrical conductor commonly used for wiring in Kenya?