[CHEM] Chapter 9 - Metals

1 DARRELL ER (COPYRIGHTED) © TOPIC 9: METALS DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Heavy content chapter • 5 key concepts • 2 advanced concepts • Always tested in exams, MCQ and FRQ • Require knowledge from chapters like:  Periodic Table, Oxidation & Reduction • Heavy-Medium overall weightage • Constitute to 5.5% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 METALS PHYSICAL PROPERTIES OF METAL ALLOYS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 PHYSICAL PROPERTIES OF METAL PHYSICAL PROPERTIES OF METAL 1) Metals are ductile (able to be stretched into wires without losing toughness). 2) Metals are malleable (able to be bent into different shapes without breaking). 3) Metals are good conductors of electricity and heat. 4) Metals have high melting and boiling points and generally are solids at room temperature. 5) Metals have high density. 6) Metals are generally strong and shiny. Exceptions: - Mercury has a low melting point (–39 ºC) and exists as a liquid at room temperature. - Group I metals such as lithium, sodium and potassium have low densities and float on water. DARRELL ER (COPYRIGHTED) ©

5 ALLOYS PURE METAL Pure metals are soft and as the layers of metal atoms would slide over one another easily when an external force is applied to them. ALLOYS Alloys are a mixtures of metals with other elements. In alloys, since the atoms have different size, the orderly arrangement of the metal atoms would be disrupted, making it tougher to slide over as easily. Hence, alloys are much stronger and harder. Examples: Steel: Iron, carbon (bodies of cars) Stainless Steel: iron, carbon, chromium, nickel (medical instruments) Brass: Copper, zinc (electrical plugs) Bronze: Copper, tin (trophies) DARRELL ER (COPYRIGHTED) ©

6 ALLOYS: STEEL STEEL Steel is a good example of an alloy that is a mixture of iron with carbon or other metals. By controlling the percentage of carbon in steel, it will form high carbon steels or low carbon steels. are softer and more easily shaped (c) state the uses of mild steel, e.g. car bodies; machinery, and stainless steel, e.g. chemical plants; cutlery; surgical instruments Mild steel will rust faster than high carbon steel due to higher iron composition - Only iron (and alloys containing iron) will rust. Magnesium corrodes Category Type of Steel Uses Special Properties Carbon Steels Mild Steel 0.25% Carbon Car bodies and machinery Hard, strong and malleable High Carbon Steel 0.45 – 1.5% Carbon Cutting and boring tools, e.g. knives, hammers Strong but brittle (more carbon atoms to prevent sliding) Alloy Steels Stainless Steel Alloy of iron, chromium, nickel & carbon. Equipments in chemical plants, cutlery, surgical instruments Extremely durable, resistant to rust and corrosion even