The World of Metals and Non-metals

Interaction with a Traditional Ironsmith in Rajasthan

In a village in Rajasthan, students Yashwant and Anandi, accompanied by their grandfather, visited a local craftsperson named Sudarshan uncle to learn about metalworking. Sudarshan, an elderly ironsmith, produces a wide variety of items for daily use and farming.

General items made by the ironsmith include flat pans ($tawas$), buckets ($baltis$), and tongs ($chimtas$). Farming tools produced at the forge include spades ($phawras$), axes ($kulhadis$), trowels ($khurpis$), and rakes ($jelees$). To create these items, Sudarshan uses iron metal and wood for handles. A furnace fueled by coal is used to heat the iron until it becomes red hot, at which point it is beaten hard with a hammer to be shaped into tools like axes.

Physical Properties of Materials: Lustre and Hardness

Materials can be categorized based on their physical appearance and tactile properties. Metals such as copper, aluminium, and iron are characterized by a distinct shine known as metallic lustre. These metals are generally very hard compared to non-metals.

In contrast, materials such as coal, sulfur ($gandhak$), and wood are non-lustrous and lack the hardness associated with metals. However, there are significant exceptions to the general rule that all metals are hard and solid:

• Soft Metals: Sodium and potassium are metals that are so soft they can be easily cut with a knife.
• Liquid Metal: Mercury is the only metal found in a liquid state at room temperature. It is commonly utilized in thermometers.

Malleability and Brittleness

Malleability is the property by which materials can be beaten into thin sheets without breaking. This property is characteristic of most metals. For instance, an iron nail, a piece of copper, or a piece of aluminium will flatten when hammered. Specific examples of malleability include silver foil used to decorate sweets and aluminium foil used for wrapping food items. Gold and silver are classified as the most malleable of all metals.

Non-metals like coal and sulfur behave differently. When hammered, they break into pieces; this property is known as brittleness. Wood is an outlier in this categorization as it neither flattens into a sheet nor breaks into pieces upon impact, meaning it is neither malleable nor brittle.

Historical Impact of Iron on Indian Civilisation

The use of metals has evolved significantly throughout history. The Harappan civilisation was known to use metals like copper and gold for utensils and jewellery, yet there is little evidence they utilized iron. Iron usage became prominent later and significantly contributed to the progress of Indian civilisation. Due to its superior strength, iron enabled the creation of high-quality agricultural tools, such as iron ploughs, which far surpassed the tools previously available. It is generally accepted that copper was discovered and used by humans earlier than iron.

Ductility of Materials

Ductility is the physical property that allows a material to be drawn into thin wires. This property is primarily possessed by metals. Examples of this include copper and aluminium wires used in electrical fittings, and metal wires used for ornaments like necklaces, earrings, and bangles. Metal wires are also essential components in stringed musical instruments such as the veena, sitar, violin, and guitar.

Gold is exceptionally ductile. It is recorded that just $1\,g$ of gold can be drawn into a wire approximately $2\,km$ in length. Non-metals like coal and sulfur are not ductile and cannot be made into wires. Additionally, ropes made of steel wires (an alloy of iron and carbon) are used in suspension bridges and cranes because they can support exceptionally heavy loads.

Sonority in Metals

Sonority is the property of materials that enables them to produce a ringing sound when struck or dropped on a hard floor. Metals are sonorous, which is why objects like metal spoons, coins, and plates produce a ringing sound. In contrast, wood and coal produce dull sounds. Practical applications of sonority include the ringing of school bells and the sound produced by $ghungroos$ (musical anklets).

Conduction of Heat

Conduction is the process by which heat is transferred from one point of a material to another. Materials that allow this transfer are called conductors. Metals are excellent conductors of heat, which is why cooking vessels are typically made of metal. Wood and plastic are poor conductors (insulators), which makes them ideal for the handles of cooking vessels to prevent burns.

In an experimental comparison (Activity 4.3), a metal spoon and a wooden spoon of similar size were placed in hot water. The metal spoon became significantly hotter to the touch at its upper end, demonstrating that heat traveled through the metal more efficiently than through the wood.

Conduction of Electricity

Materials are classified based on their ability to allow the flow of electricity:

• Good Conductors: Materials that allow electricity to flow through them easily. Metals like aluminium, iron, and copper are good conductors. This is demonstrated when these materials are used in a 'tester' circuit, causing the bulb to glow.
• Poor Conductors: Materials that prevent the flow of electricity. Examples include sulfur, coal, wood, stone, rubber, and nylon.

Electricians use these properties for safety, employing tools with plastic handles and wearing rubber gloves and shoes. Because plastic and rubber are poor conductors, they protect workers from electric shocks.

Corrosion and the Rusting of Iron

Corrosion is the gradual deterioration of metal surfaces caused by exposure to air, water, or other chemicals in the atmosphere. The most common form of corrosion is the rusting of iron. Rust is the brown, flaky deposit that forms on iron when it is exposed to moist air.

Through Activity 4.5, it was determined that both air and water must be present for iron to rust:

• Bottle A: Iron nail + silica gel (dry air) = No rust.
• Bottle B: Iron nail + boiled water + oil layer (no air) = No rust.
• Bottle C: Iron nail + air + water = Rust forms.

Other metals also corrode; for example, copper develops a green coating and silver develops a black coating when exposed to the atmosphere. Rusting is a major economic issue, requiring significant funds for the repair and replacement of iron structures. Prevention methods include painting, oiling, greasing, and galvanisation (applying a protective layer of zinc).

The Iron Pillar of Delhi

The Iron Pillar located in Delhi serves as a testament to ancient Indian metallurgy. Created during the reign of Chandragupta II more than $1600$ years ago, the pillar stands approximately $8\,m$ high and weighs more than $6000\,kg$. Despite being exposed to the elements for over a millennium, it has resisted rusting, showcasing the advanced metal technology of that era.

Chemical Reactions of Metals and Non-metals with Oxygen

Metals and non-metals react with oxygen in the air to form oxides, which have different chemical natures:

• Metals: When magnesium ribbon (a metal) is burned, it produces a dazzling white flame and forms a white powder called magnesium oxide ($MgO$). When this powder is dissolved in water, the solution turns red litmus paper blue, indicating that metal oxides are generally basic in nature. Sodium is another metal that reacts vigorously with oxygen and water; it is stored in kerosene to prevent accidental reaction with moisture and air.
• Non-metals: When sulfur (a non-metal) is burned in a deflagrating spoon, it produces sulfur dioxide gas ($SO_2$). When this gas is dissolved in water, it forms sulfurous acid. This solution turns blue litmus paper red, indicating that non-metal oxides are generally acidic in nature. Unlike metals, most non-metals do not react with water. Phosphorus is a non-metal that catches fire when exposed to air and is therefore stored in water for safety.

Elements and the Classification of Matter

Metals and non-metals are sub-categories of elements. An element is a substance that cannot be broken down into simpler substances. There are currently $118$ known elements, which serve as the basic building blocks of all matter. Some occur naturally, while others are artificially synthesized in laboratories.

The Importance of Non-metals in Daily Life

While metals are valued for their strength and conductivity, non-metals are also essential for survival and industry:

• Oxygen: A non-metal required for respiration by all living organisms.
• Carbon: The fundamental building block of lifeforms; it is a key component of proteins, fats, and carbohydrates.
• Nitrogen: Essential for plant growth and used in the manufacture of fertilisers.
• Chlorine: Widely used in the purification of water.
• Iodine: Used as an antiseptic solution applied to wounds.

Sustainability and Modern Technology

Metals and their alloys (mixtures of metals or metals and non-metals) are critical for modern industry, aerospace (titanium), and atomic energy (zirconium). In India, metals like iron and aluminium are frequently recycled to minimize waste and promote sustainability.

Questions & Discussion

Which metal is commonly used for food packaging? Aluminium is used because it is inexpensive and its thin sheets are easily folded into various shapes.

Which metal catches fire when in contact with water? Sodium reacts vigorously and generates a lot of heat when in contact with water.

Is it true that copper vessels are used for boiling water because they are good conductors of electricity? False. Copper is used for boiling water because it is an excellent conductor of heat, not because of its electrical conductivity in that specific context.

What happens when oxygen reacts with magnesium and sulfur? Oxygen reacts with magnesium to form basic magnesium oxide, and with sulfur to form acidic sulfur dioxide.