1. Introduction to Metals and Their Physical Properties

The study of materials in our surroundings, particularly in the Indian context, reveals a deep-rooted history of metalwork. From the local ironsmiths in Rajasthan making tawas to high-tech industries, metals are fundamental to our civilization.

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Malleability: Shaping Materials

This property defines how a material responds to mechanical stress such as hammering. Most metals are malleable, whereas non-metals are not.

• Definition: Malleability is the property by which materials can be beaten into thin sheets without breaking.
• Observation of Metals: When an iron nail, a piece of copper, or aluminium is hammered, it flattens into a sheet.
• Daily Life Examples:
  • Silver Foil (Chandi ka Vark): Used to decorate traditional Indian sweets.
  • Aluminium Foil: Widely used for wrapping and preserving food items.
• Brittleness in Non-metals: Materials like coal and sulfur (Gandhak) are brittle. They break into small pieces when struck.
• Lustre and Hardness:
  • Metals generally possess metallic lustre (a shiny appearance).
  • They are typically hard, but there are notable exceptions:
    • Sodium and Potassium: These metals are so soft they can be cut with a knife.
    • Mercury: The only metal found in a liquid state at $room \ temperature$.

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Ductility: Drawing into Wires

The ability of materials to change their shape into long, thin strands is a vital industrial property possessed by metals.

• Definition: Ductility is the property by which a material can be drawn into wires.
• Highly Ductile Metals:
  • Gold: The most ductile metal. Approximately $1 \text{ gram}$ of gold can be drawn into a wire $2 \text{ kilometres}$ long!
  • Copper and Aluminium: Used extensively for electrical fittings in Indian homes.
• Applications:
  • Musical Instruments: Metal wires are essential for the strings of the Veena, Sitar, Violin, and Guitar.
  • Jewellery: Intricate designs in bangles and earrings are made possible due to ductility.
  • Construction: Ropes made of steel wires (an alloy of iron and carbon) are used in suspension bridges and cranes to lift heavy loads.
• Non-metals: Materials like coal and sulfur cannot be drawn into wires; they are non-ductile.

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Sonority: The Ringing Sound

The acoustic property of metals is distinct from that of non-metals, which is why they are used to create sound-producing objects.

• Definition: Sonority is the property of metals that enables them to produce a ringing sound when struck.
• Observations:
  • A metal coin or spoon dropped on the floor produces a sharp, ringing sound.
  • A wooden block or piece of coal produces a dull sound.
• Cultural and Functional Uses:
  • School Bells: Traditionally made of metal to ensure the sound reaches all classrooms.
  • Ghungroos: Used by Indian classical dancers, these produce a rhythmic ringing sound due to the sonorous nature of metals.
  • Temple Bells: Large metal bells are designed specifically to exploit this property.

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Comparison of Physical Properties

The following table summarizes the behavior of different materials based on the properties discussed above:

Material	Appearance	Malleability	Ductility	Sonority
Iron / Copper	Lustrous	Malleable	Ductile	Sonorous
Aluminium	Lustrous	Malleable	Ductile	Sonorous
Coal / Sulfur	Dull	Brittle	Non-ductile	Non-sonorous
Wood	Dull	Non-malleable	Non-ductile	Non-sonorous

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2. Conduction of Heat and Electricity

The ability of a material to allow energy to flow through it is a defining characteristic used to classify metals and non-metals. This energy transfer can occur in two primary forms: Thermal (Heat) and Electrical.

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Conduction of Heat

Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. Metals are renowned for being excellent conductors of heat.

Activity 4.3: Investigating Heat Transfer

• Experimental Setup: Immerse a metal spoon and a wooden spoon of similar size in a glass tumbler filled with hot water.
• Observation: After a few minutes, touch the upper ends of both spoons.
• Findings:
  • The metal spoon becomes hot to the touch because heat from the water travels to the other end.
  • The wooden spoon remains relatively cool, indicating that wood is a poor conductor.

Practical Applications in Indian Kitchens

• Cooking Vessels: Most utensils like Tawas, Kadhais, and Pressure Cookers are made of Aluminium, Copper, or Stainless Steel to ensure efficient cooking.
• Insulated Handles: To prevent burn injuries, handles are made of wood, plastic, or Bakelite because these materials do not conduct heat.

Material Type	Heat Conductivity	Examples
Metals	Good Conductors	Iron, Copper, Aluminium, Silver
Non-metals/Other	Poor Conductors (Insulators)	Wood, Plastic, Glass, Coal

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Conduction of Electricity

Materials that allow electric current to pass through them easily are known as good conductors of electricity. This property is fundamental to the functioning of all electrical appliances.

Activity 4.4: Testing Electrical Conductivity

Using a tester circuit (comprising a cell, a bulb, and connecting wires), we can test various substances:

• Conductors: Objects like Iron nails, Copper wires, and Aluminium foil complete the circuit, making the bulb glow.
• Insulators: Materials such as Sulfur, Coal, Rubber, and Dry Wood break the circuit, and the bulb does not glow.

Safety Measures for Electricians

• Electricians use tools like screwdrivers that have plastic or rubber handles.
• They often wear rubber gloves and shoes while working on live wires to protect themselves from electric shocks.

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Mathematical Expression for Resistance

The resistance of a material ($R$) is its tendency to oppose the flow of electric current. It is mathematically derived based on the dimensions of the material:

$R = \rho \cdot \frac{L}{A}$

Where:

• $R$ is the Resistance (measured in $\Omega$).
• $\rho$ (rho) is the Resistivity (a constant property of the material).
• $L$ is the Length of the conductor.
• $A$ is the Cross-sectional area of the conductor.

Note: Since Metals have extremely low resistivity ($\rho$), they serve as Good Conductors.

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3. Chemical Properties: Reaction with Air and Water

Chemical properties describe how a substance changes into a completely new substance through reactions. Metals and non-metals show distinct behaviors when they interact with the oxygen in the air and with water.

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Reaction with Oxygen (Air)

Most elements react with oxygen to form oxides. However, the nature of these oxides is the primary difference between metals and non-metals.

A. Metals and Basic Oxides

• General Rule: Metals react with oxygen to produce metal oxides which are basic in nature.
• Example (Magnesium): When a magnesium ribbon is burnt in air, it produces a dazzling white flame and forms a white powder called Magnesium Oxide ($MgO$).
• Chemical Reaction:

  $2Mg + O_2 \rightarrow 2MgO$

• Testing the Nature: When $MgO$ is dissolved in water, it forms Magnesium Hydroxide. This solution turns red litmus paper to blue, proving it is a base.
• Vigorous Reaction (Sodium): Some metals like Sodium are so reactive that they catch fire in open air or water. Hence, they are stored in kerosene to prevent accidental reactions.

B. Non-metals and Acidic Oxides

• General Rule: Non-metals react with oxygen to form non-metallic oxides which are acidic in nature.
• Example (Sulfur): Burning sulfur in a deflagrating spoon produces Sulfur Dioxide ($SO_2$) gas.
• Reaction in Water: If $SO_2$ is dissolved in water, it forms Sulfurous Acid ($H_2SO_3$).
• Chemical Reaction:

  $S + O_2 \rightarrow SO_2$

  $SO_2 + H_2O \rightarrow H_2SO_3$

• Testing the Nature: The resulting solution turns blue litmus paper to red, confirming it is an acid.

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Rusting and Corrosion of Metals

Corrosion is the gradual wearing away of metal surfaces due to the action of air, moisture, or chemicals. The most famous example is the rusting of iron.

Rusting of Iron

• Essential Conditions: For iron to rust, both air (oxygen) and water (moisture) must be present.
• Experimental Evidence:
  1. In Dry Air (with silica gel): Iron does not rust.
  2. In Boiled Water (with oil layer to block air): Iron does not rust.
  3. In Moist Air: Iron rusts quickly, forming a brown flaky deposit.
• Chemical Formula of Rust: Rust is Hydrated Iron Oxide.

  $4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3 \cdot xH_2O$

Corrosion of Other Metals

• Copper: Develops a dull green coating (mixture of copper hydroxide and copper carbonate) when exposed to moist air for long periods.
• Silver: Develops a black coating over time due to reaction with sulfur compounds in the air.

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Prevention of Rusting

In India, enormous amounts of money ($\text{₹}$) are spent annually to repair or replace rusted iron structures like bridges and railings. Common prevention methods include:

• Painting or Oiling: Applying a layer of paint or grease to block air and moisture.
• Galvanisation: The process of depositing a thin layer of Zinc on iron objects to protect them from rusting.
• Alloying: Mixing iron with other metals/non-metals (e.g., Stainless Steel) to make it rust-resistant.

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Ancient Indian Metallurgy: The Iron Pillar

The Iron Pillar of Delhi (near Qutub Minar) is a world-renowned marvel of ancient Indian science. Built over $1600$ years ago, it weighs more than $6000 \text{ kg}$. Despite centuries of exposure to rain and sun, it has barely any rust. This proves that Indian craftspersons had developed advanced technology to resist corrosion long before modern science.

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Reaction with Water

• Metals: React with water with varying speeds. Sodium reacts vigorously, whereas Iron reacts very slowly.
• Non-metals: Generally, non-metals do not react with water. This property is used to store highly reactive non-metals. For example, Phosphorus is stored in water because it catches fire immediately if exposed to air.

4. Elements and the Importance of Non-metals

Every substance in the universe is made up of fundamental building blocks called Elements. These are the simplest forms of matter that cannot be broken down further by chemical reactions such as heating or electrolysis.

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The Concept of Elements

Understanding the nature of elements is the foundation of chemistry:

• Total Known Elements: Currently, there are 118 elements known to science.
• Nature of Elements: Some elements occur naturally in the Earth's crust, while others are artificially synthesized in laboratories.
• Sub-categories: Elements are primarily classified into two groups: Metals and Non-metals.

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Characteristics of Non-metals

Non-metals are substances that display properties opposite to those of metals. Their general features include:

• Physical State: They can be solids, liquids, or gases at room temperature.
• Appearance: Most non-metals are dull and non-lustrous (except iodine, which is shiny).
• Mechanical Properties: They are brittle (break into pieces when hammered) and non-ductile (cannot be made into wires).
• Conductivity: They are generally poor conductors of heat and electricity.
• Oxide Nature: When non-metals react with oxygen, they form acidic oxides.

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Vital Uses of Non-metals in Daily Life

Although non-metals may lack the physical strength of metals, they are indispensable for the existence of life and modern industry.

Non-metal	Primary Use and Importance
Oxygen	Crucial for Respiration; living organisms cannot survive without breathing it.
Carbon	The basic building block of all life forms; present in proteins, fats, and carbohydrates.
Nitrogen	Essential for Plant Growth; used extensively in the manufacturing of chemical fertilisers.
Chlorine	Acts as a powerful disinfectant used in water purification to kill germs.
Iodine	Used in the form of a solution as an antiseptic to treat wounds and prevent infection.
Phosphorus	Highly reactive; used in matchsticks and certain types of fertilisers.

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Ancient Indian Metallurgy: A Historical Marvel

India has been a global leader in metal technology for thousands of years. The Iron Pillar of Delhi stands as a testament to this ancient expertise.

• Age: It was constructed more than 1600 years ago during the reign of Chandragupta II.
• Dimensions: The pillar is about $8$ metres high and weighs over $6000$ kilograms.
• Unique Property: Despite centuries of exposure to monsoon rains, harsh sunlight, and humidity, it has barely any rust.
• Significance: This resistance to corrosion proves that ancient Indian craftspersons possessed advanced chemical knowledge to prevent the rusting of iron.

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Science, Society, and Sustainability

In modern India, the management of metal resources is crucial for the economy and the environment:

• Alloys: We use Alloys (mixtures of metals with other elements) like Steel or Brass for making utensils and industrial tools.
• Recycling: Metals like Iron and Aluminium are recycled on a large scale in India to minimize waste and promote Sustainability.
• Specialized Metals: Elements like Zirconium are used in Atomic Energy, while Titanium is essential for Aerospace technologies.

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Summary of Element Classification

The distinction between elements is vital for their application:

1. Metals: Chosen for strength, conductivity, and durability (e.g., Copper wires, Iron tools).
2. Non-metals: Chosen for biological processes, chemical reactions, and purification (e.g., Oxygen for breathing, Chlorine for water).

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