The World of Metals and Non-metals

Chapter at a Glance

This chapter explores the distinct physical and chemical properties of metals and non-metals. It explains key properties such as malleability, ductility, sonority, and thermal/electrical conductivity, contrasting how metals (like iron, copper, and aluminium) and non-metals (like sulfur and carbon) behave under physical stress. The chemical behavior of these elements is investigated through their reactions with oxygen and water, establishing that metal oxides are basic while non-metal oxides are acidic. The chapter also covers the process of corrosion and rusting of iron, outlining prevention methods, and highlights the historical achievements of Indian metallurgy (like the Delhi Iron Pillar) and the everyday importance of non-metals.

Key Definitions & Terminology

Metallic Lustre: The characteristic shiny, reflective surface appearance of metals.
Malleability: The physical property that allows a material to be beaten or hammered into thin sheets without breaking or cracking.
Ductility: The physical property that allows a material to be drawn or stretched into thin wires.
Sonority: The property of producing a deep, ringing sound when struck.
Brittleness: The tendency of a material to fracture or break into pieces when subjected to mechanical stress (typical of solid non-metals like coal or sulfur).
Corrosion: The gradual deterioration of a metal's surface due to chemical reactions with air, moisture, or chemical substances in the environment.
Rusting: The specific corrosion of iron in which a flaky, brown hydrated iron oxide (rust) forms in the presence of both oxygen and moisture.
Galvanisation: The rust-prevention method of coating iron with a thin layer of zinc metal.
Element: A pure chemical substance composed of only one type of atom that cannot be broken down into simpler substances. There are 118 known elements.
Alloy: A homogeneous mixture of two or more metals, or a metal and a non-metal (e.g., steel).

Formulas, Rules & Properties

Rusting Chemical Equation:
$$\text{Iron (Fe)} + \text{Oxygen (O}_2\text{)} + \text{Water (H}_2\text{O)} \rightarrow \text{Rust (Hydrated Iron Oxide)}$$
Both air (oxygen) and water (moisture) must be simultaneously present for rusting to occur.
Magnesium Oxide Reaction (Basic):
$$\text{Magnesium (Mg)} + \text{Oxygen (O}_2\text{)} \xrightarrow{\text{Heat}} \text{Magnesium Oxide (MgO) [White Ash]}$$
MgO dissolves in water to form magnesium hydroxide ($\text{Mg(OH)}_2$), which turns red litmus paper blue (basic).
Sulfur Oxide Reaction (Acidic):
$$\text{Sulfur (S)} + \text{Oxygen (O}_2\text{)} \xrightarrow{\text{Heat}} \text{Sulfur Dioxide (SO}_2\text{)}$$
$\text{SO}_2$ dissolves in water to form sulfurous acid ($\text{H}_2\text{SO}_3$), which turns blue litmus paper red (acidic).
Key Exceptions in Element Properties:
Mercury ($Hg$): The only metal found in a liquid state at room temperature.
Sodium ($Na$) and Potassium ($K$): Metals that are so soft they can be cut easily with a knife.
Sodium ($Na$): Extremely reactive with oxygen and water; must be stored in kerosene.
Phosphorus ($P$): A highly reactive non-metal that catches fire in air; must be stored in water.

Core Concepts & Topics

History and Progress of Metallurgy:
The Harappans utilized copper and gold for utensils and jewelry but did not use iron.
The later discovery and widespread adoption of iron implements (such as iron ploughshares) significantly advanced Indian agriculture and trade.
The Delhi Iron Pillar:
A historical landmark of Indian metallurgy constructed over 1600 years ago during Chandragupta II's reign. Weighing over 6000 kg and standing 8 meters tall, it remains virtually rust-free due to its unique chemical composition and rust-resistant passive film.
Everyday Uses of Non-metals:
Oxygen: Indispensable for respiration in living organisms.
Carbon: The foundational element of all organic life forms, forming proteins, fats, and carbohydrates.
Nitrogen: Used to manufacture plant fertilizers to boost crop health.
Chlorine: Used in municipal water purification.
Iodine: Used as a mild antiseptic solution on wounds.
Elements vs. Compounds:
Common insulating materials like plastic, glass, wood, rubber, and paper are compounds, not elements, and are not classified under metals or non-metals.
Ironsmith Hammering Principles:
Heating iron until it is red-hot increases its malleability, making it pliable enough to be hammered into shapes like axes and pans.

Worked Examples

CHEAPEST PACKAGING MATERIAL:
Question: Which metal is commonly used for food packaging because it is cheap and easily folded?
Solution: Aluminium (Option i), due to its high malleability and lightweight nature.
WATER REACTIVE METAL:
Question: Which metal catches fire when it comes in contact with water?
Solution: Sodium (Option iv), due to its highly exothermic reaction with water.
True or False checks:
(i) Aluminium and copper are non-metals used for utensils. $\rightarrow$ False (they are metals).
(ii) Metal oxides turn blue litmus to red. $\rightarrow$ False (they are basic, turning red litmus blue).
(iii) Oxygen is a non-metal essential for respiration. $\rightarrow$ True.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity. $\rightarrow$ False (they are used because they conduct heat exceptionally well, not electricity).
Suitability for Jewellery:
Question: Why are only a few metals suitable for making jewellery?
Solution: Metals like gold, silver, and platinum are used because they have high metallic lustre, are highly malleable and ductile, and are chemically inert (do not react with air, water, or mild acids, so they do not tarnish).
Match the Columns:
(i) Used in electrical wiring $\rightarrow$ P E P O R C (Copper, c).
(ii) Most malleable and ductile $\rightarrow$ O G D L (Gold, e).
(iii) Living organisms cannot survive without it $\rightarrow$ E N X Y G O (Oxygen, a).
(iv) Plants grow healthy with fertilisers containing it $\rightarrow$ T E N G O I N R (Nitrogen, d).
(v) Used in water purification $\rightarrow$ N E C O H I R L (Chlorine, b).
Reactions of Magnesium and Sulfur with Oxygen:
Question: Compare the reaction of magnesium and sulfur with oxygen.
Solution: Magnesium reacts to form MgO, which behaves as a base in water and turns red litmus blue. Sulfur reacts to form $\text{SO}_2$, which dissolves to form sulfurous acid, turning blue litmus red.
Boiling Pan Material Selection:
Question: Choose the best material to make a water boiling pan from: Iron, copper, sulfur, coal, plastic, wood, cardboard.
Solution: Copper is the best choice because it has the highest thermal conductivity among the options, does not melt or burn like plastic, wood, or cardboard, and is highly malleable and durable.
Corrosion of Nails in Different Fluids:
Question: Three iron nails are dipped in: (1) oil, (2) water, (3) vinegar. Which will not rust, and why?
Solution: The nail in oil will not rust because oil cuts off access to both oxygen and water. The nail in vinegar will undergo rapid acid corrosion, and the nail in water (if exposed to air) will rust.
Can Sulfur protect Iron?:
Question: Can sulfur be used to coat iron to prevent rusting?
Solution: No. Sulfur is a non-metal and is highly brittle, so it cannot be hammered or drawn into a cohesive, adhesive protective layer. It is also highly flammable and melts at a low temperature.

Practical Activities & Experiments

Activity 4.1 (Hammering Hammer test): Hammering copper, aluminium, iron, coal, sulfur, and wood to classify them as malleable or brittle.
Activity 4.2 (Sonority test): Dropping metal spoons/coins vs. wood/coal to note ringing vs. dull sounds.
Activity 4.3 (Thermal Conduction): Immersing metal and wooden spoons in hot water to prove that metal conducts heat.
Activity 4.4 (Conduction Tester): Testing foils, nails, wires, sulfur, and erasers in a tester circuit to identify electrical conductors.
Activity 4.5 (Rusting Variables): Placing iron nails in bottles with: (A) silica gel (dry air), (B) boiled water + oil (no air), and (C) open water + air, to prove that both air and water are needed for rusting.
Activity 4.6 (Burning Magnesium): Igniting Mg ribbon to produce white MgO ash, dissolving it in water, and proving its basic nature using litmus.
Activity 4.7 & 4.8 (Burning Sulfur): Heating sulfur, collecting and dissolving the $\text{SO}_2$ gas, and demonstrating its acidic properties using litmus paper.

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