metals and non metals

4.1 Properties of Materials

  • Context and scene: Yashwant and Anandi in a Rajasthan village visit ironsmith Sudarshan uncle to learn how metals are shaped into daily-use items. Items mentioned include flat pans (tawas), buckets (baltis), tongs (chimtas), farming tools like spades (phawras), axes (kulhadis), trowels (khurpis), and rakes (jelees). Materials used include iron for the items and wood for handles; coal is used to heat the iron in the furnace. The iron is heated until red-hot and beaten with a hammer to shape (demonstrates malleability of metals). Anandi asks if other metals can be shaped similarly.
  • Core idea: Metals can be manipulated (beat into shape, drawn into wires, etc.) due to their distinct properties. The chapter explores malleability, ductility, sonority, and conductivities as core metal properties, with practical examples and safe, classroom-friendly experiments.

4.1.1 Malleability

  • Definition and concept:
    • Malleability is the property by which materials can be beaten into thin sheets or flattened without breaking.
    • This property is common to most metals; it enables the making of sheets like gold/silver foils and aluminium foil.
  • Activity 4.1 (observational and practical):
    • Caution: Conduct under teacher/adult supervision.
    • Materials to collect: waste pieces of copper and aluminium, an iron nail, a lump of coal, a pea-sized lump of sulfur (gandhak), and a block of wood.
    • Tasks:
    • Observe appearances (lustrous or non-lustrous) and hardness/softness of each item.
    • Predict what happens when each item is placed on a hard surface and beaten with a hammer.
    • Record observations for each item in Table 4.1 (Appearance, hardness, and effect of hammering).
  • Table 4.1 (summary interpretation):
    • Piece of copper, piece of aluminium, and iron nail are lustrous and hard; they become flattened when beaten (show malleability).
    • Lump of sulfur, coal, and block of wood are non-lustrous; coal and sulfur are not easily flattened into sheets and tend to break; wood is neither malleable nor brittle.
  • Key concepts:
    • Objects made from copper, aluminium, and iron are lustrous and hard, demonstrating metallic lustre and hardness; these metals are malleable.
    • Non-metals like coal and sulfur are non-lustrous and brittle under hammering; wood is neither malleable nor brittle in the metallic sense.
    • Metallic lustre defines many metals; metallic lustre is the shine typical of metals.
  • Important definitions and examples:
    • Metals: typically lustrous, malleable, ductile, hard (varies by metal), and good conductors of heat and electricity.
    • Non-metals: often non-lustrous (dull), brittle or non-malleable, and poor conductors of heat and electricity.
    • Mallet-based shaping demonstration confirms malleability as a key property of metals.
  • Foundational references:
    • Observations connect to Grade 6 chapter Materials Around Us (recalled in the activity).
    • The discussion links malleability to practical uses (e.g., metal sheets such as foil).
  • Notes and takeaways:
    • Gold and silver are highlighted as the most malleable metals.
    • Not all materials are malleable; sulfur and coal are brittle; wood is not malleable in this sense.
    • The practical application of malleability underpins metalworking and tool/utensil fabrication.

4.1.2 Ductility

  • Definition and concept:
    • Ductility is the property of a material to be drawn into wires; metals primarily possess this property.
  • Real-world examples and implications:
    • Metal wires (copper, aluminium) are used in electrical fittings and in making strings for musical instruments (veena, sitar, violin, guitar).
    • Gold is exceptionally ductile: 1 g1~\mathrm{g} of gold can be drawn into a 2 km-long2~\mathrm{km}\text{-long} wire.
  • Significance:
    • Ductility supports the production of long, thin wires essential for electrical systems, cables, and musical instrument strings.
  • Observations and connections:
    • The ductile nature of metals enables manufacturing and engineering feats (e.g., long gold wires), illustrating why metals are often preferred for wires and cables.

4.1.3 Sonority

  • Definition and concept:
    • Sonority is the property of producing a ringing sound when struck or dropped, characteristic of many metals.
  • Activity 4.2 (investigation of sound):
    • Items to compare: metal spoon, metal coin, coal, and wood.
    • Observation: metal objects tend to emit a ringing or resonant sound when dropped, while coal/wood produce dull sounds.
  • Key takeaway:
    • Metals are sonorous; this property is a diagnostic feature distinguishing metals from many non-metals.
  • Everyday relevance:
    • The ringing of bells, metal utensils, and instruments is explained by metal sonority.

4.1.4 Conduction of heat

  • Concept:
    • Conduction is the transfer of heat from one point to another within a material.
    • Metals generally transfer heat efficiently (good conductors); wood transfers heat poorly (poor conductor).
  • Activity 4.3 (heat conduction experiment):
    • Setup: place a metal spoon and a wooden spoon in hot water of the same temperature; after a few minutes, touch the upper ends to compare heat transfer.
    • Observation and conclusion:
    • The metal spoon becomes hotter to touch than the wooden spoon because heat is conducted along the metal more effectively.
    • Wood is a poor conductor, so its heat transfer is slower.
  • Implications for cooking:
    • Metals are preferred for cooking vessels due to good heat conduction; handles are often made of wood or other non-conductors to prevent burns.
  • Terms:
    • Conductors: materials that readily transfer heat (e.g., metals).
    • Insulators: materials that do not transfer heat well (e.g., wood, plastic).

4.1.5 Conduction of electricity

  • Concept:
    • Conductivity of electricity: metals are generally good conductors; many non-metals are insulators.
  • Activity 4.4 (electric circuit design):
    • Materials provided: aluminium foil, iron nail, lump of sulfur (pea-sized), copper wire, coal, dry wood, stone, eraser of rubber, nylon rope.
    • Task: predict which objects will make a bulb glow; test and record results in Table 4.2.
    • Observations:
    • Good conductors: aluminium, iron, copper (bulbs glow).
    • Poor conductors: sulfur, coal, wood, stone, rubber eraser, nylon rope (bulbs do not glow).
  • Conclusions:
    • Metals are good conductors of electricity; many non-metals and insulating materials prevent current flow.
    • Practical safety implication: electricians use rubber gloves and plastic insulation to prevent electric shocks due to poor conductors of electricity.

4.2 Effect of Air and Water on Metals: Iron

  • Observation about rusting:
    • Iron objects develop brown deposits (rust) only when exposed to both air and water over time.
    • Bottle A: dry air; No rust.
    • Bottle B: water only (no air); No rust.
    • Bottle C: both water and air; Rust forms on the iron nail.
  • Conclusion:
    • Moist air (presence of both water and air) is essential for rusting; rust is a form of corrosion and deteriorates iron surfaces.
  • Important definitions:
    • Rust: brown deposits on iron caused by iron oxidation and hydration; the process is rusting.
    • Corrosion: gradual deterioration of metal surfaces due to air, water, or other substances.
  • Prevention methods discussed (to be learned in higher grades):
    • Painting, oiling, greasing, and applying a protective layer of zinc (galvanisation) to protect iron from rust.
  • Holistic lens: The Iron Pillar of Delhi (an example of ancient metallurgy):
    • The Iron Pillar is about 8 m8~\mathrm{m} tall and weighs more than 6 000 kg6\,000\ \mathrm{kg}.
    • Remarkably, despite centuries of exposure to wind and rain, it shows very little rust, highlighting advanced metalworking techniques in ancient India.
    • This illustrates long-standing metallurgical knowledge and its impact on civilization.

4.3 Effect of Air and Water on Other Metals

  • Activity 4.6 (demonstration): burning of a metal ribbon (magnesium) to explore metal oxidation.
  • Steps and observations:
    • A magnesium ribbon (3–4 cm) is ignited and burns with a dazzling white flame, forming magnesium oxide (MgO).
    • The white powder collected on a watch glass is MgO.
    • When a few drops of warm water are added to the powder, the solution is tested with a pH indicator.
    • Result: MgO solution is basic (blue/red litmus test shows basicity) because: oxides of metals are typically basic.
  • Chemical reaction (for Mg oxidation):

    2\,\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\,\mathrm{MgO}
  • Implication:
    • Metals form basic oxides that can affect the pH of solutions when dissolved.

4.4 Substances that Behave Differently from Metals in Air and Water

  • Sulfur and phosphorus are examples of non-metals that react differently from metals with air and water.
  • Demonstrations and observations:
    • Burning sulfur in air produces sulfur dioxide gas; when dissolved in water, sulfurous acid forms (SO$2$ + H$2$O → HSO$_3^-$ or related equilibria).
    • In a demonstration called 4.7, deflagration of sulfur and subsequent testing with water indicates the produced solution is acidic in nature (acidic oxides).
  • Characteristics of non-metals:
    • Generally dull in appearance, not malleable or ductile, not sonorous.
    • Poor conductors of heat and electricity (insulators in many cases).
    • Their oxides are typically acidic in nature.
  • Examples of non-metals and uses:
    • Oxygen (O$_2$) – essential for respiration; used in combustion and life processes.
    • Nitrogen (N$_2$) – used in fertilizers and various chemicals;
    • Carbon (C) – building block of organic life; essential in proteins, fats, carbohydrates.
    • Chlorine (Cl) – used in water purification.
    • Iodine (I) – antiseptic for wounds.
  • Important distinction:
    • Metals and non-metals are sub-categories of elements; elements are fundamental building blocks; there are 118118 known elements.
    • Metals and non-metals have wide applications but differ in properties and reactivity.
  • Summary of non-metals in everyday life:
    • They play essential roles (e.g., oxygen in respiration, carbon in organic matter, nitrogen in fertilizers, chlorine in water treatment, iodine in antiseptics).
  • What to remember about non-metals:
    • They are generally poor conductors, not malleable/ductile, and their oxides are typically acidic.
    • They contrast with metals in many properties, yet both groups are crucial for daily life and technology.

4.5 Are Non-metals Essential in Everyday Life?

  • Emphases:
    • Although metals have standout properties (lustre, strength, conductivity), non-metals are indispensable for life and modern processes.
    • Oxygen is essential for respiration; carbon is the backbone of organic molecules; nitrogen is key for fertilizers and chemical synthesis; chlorine purifies water; iodine is antiseptic.
  • Science and society:
    • Metals and alloys underpin utensils, tools, and modern technologies; they are also recycled to promote sustainability.
    • Some metals and alloys are used in specialized technologies (e.g., zirconium in nuclear energy, titanium in aerospace).
  • In a Nutshell (summary):
    • Metals vs non-metals can be differentiated by properties: lustre, malleability, ductility, conduction of heat/electricity, reaction with oxygen, etc.
    • Metals are usually lustrous, malleable, ductile, and good conductors; non-metals are often dull, non-malleable/ductile, and poor conductors.
    • Metals form basic oxides; non-metals form acidic oxides.
    • Both groups have wide applications in everyday life and technology.

Let Us Enhance Our Learning (practice and reflection)

  • 1. Which metal is commonly used to make food packaging materials as it is cheaper and its thin sheets can be folded easily into any shape? (i) Aluminium (ii) Copper (iii) Iron (iv) Gold
  • 2. Which metal catches fire when it comes in contact with water? (i) Copper (ii) Aluminium (iii) Zinc (iv) Sodium
  • 3. True/False statements:
    • (i) Aluminium and copper are examples of non-metals used for utensils and statues. [ F ]
    • (ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red. [ F ]
    • (iii) Oxygen is a non-metal essential for respiration. [ T ]
    • (iv) Copper vessels are used for boiling water because they are good conductors of electricity. [ F ]
  • 4. Why are only a few metals suitable for making jewellery?
  • 5. Match the uses of metals and non-metals given in Column I with the jumbled names of metals and non-metals given in Column II. (This is a matching exercise with given options.)
    • Column I: (i) Used in electrical wiring (ii) Most malleable and ductile (iii) Living organisms cannot survive without it. (iv) Plants grow healthy when fertilisers containing it are added to the soil. (v) Used in water purification
    • Column II options: (e) O G D L, (d) T E N G O I R, (c) P E P O R C, (b) N E C O H I R L, (a) E N X Y G O
  • 6. What happens when oxygen reacts with magnesium and sulfur? What are the main differences in the nature of products formed?
  • 7. Complete the following flow chart: ? ? Add blue and red litmus solutions separately ? Blue Change in blue litmus solution Change in red litmus solution Air Heat Ash Water
  • 8. Choose a material to make a pan most suitable for boiling water and explain why (iron, copper, sulfur, coal, plastic, wood, cardboard).
  • 9. You are provided with three iron nails dipped in oil, water, and vinegar. Which iron nail will not rust, and why?
    1. How do the different properties of metals and non-metals determine their uses in everyday life?
    1. One method of protecting iron from rust is applying a thin coating of zinc. Since sulfur does not react with water, can it be used for this purpose? Justify.
    1. Why is heating iron necessary before making tools with an ironsmith?
  • Exploratory Projects:
    • Dhokra, Bidriware, Pembarthi, and Kamrupi are famous metal art styles in India. Identify the states where they are made and create a collage of photographs.
    • Mark on a map the states where iron, gold, aluminium, and other metals are found.
    • Explore metals and non-metals in smartphones and their role in phone functionality.
    • Organize a classroom debate on whether the use of metals should be increased or decreased for comfort and luxury.
  • Disciplinary connections: Interdisciplinary links across Science, Society, Art, Economy, Geography, Technology, History.
  • DIVE DEEPER: 4.5 (Magnesium burning) and 4.7 (Non-metal behavior and sulfur) are demonstrations that illustrate oxidation, basic oxides, and gas evolution.

Fascinating Facts

  • The Iron Pillar of Delhi had remarkable rust resistance despite being over 1600 years old and about 8 m tall with a weight exceeding 6 000 kg6\,000\ \mathrm{kg}; this highlights ancient Indian metallurgical skills and the durability of certain metal structures.

Quick Recap (In a Nutshell)

  • Metals and non-metals are differentiated by properties such as lustre, malleability, ductility, and conductivity.
  • Metals: typically lustrous, malleable, ductile, and good conductors of heat and electricity.
  • Non-metals: often dull, not malleable/ductile, and poor conductors; many form acidic oxides.
  • Metal oxides are usually basic; non-metal oxides are usually acidic.
  • Metals rust/corrode in moist air; prevention includes painting, oiling, greasing, and galvanisation.
  • Both metals and non-metals have vital roles in daily life, industry, and advanced technologies.

Key Formulas and Numerical References (LaTeX)

  • Ductility example: 1 g1~\mathrm{g} of gold can be drawn into a 2 km-long2~\mathrm{km}\text{-long} wire.
  • Iron pillar: height 8 m8~\mathrm{m}; weight > 6\,000~\mathrm{kg}.
  • Rust chemical concept: rust is Fe<em>2O</em>3⋅nH2O\mathrm{Fe<em>2O</em>3 \cdot nH_2O} (iron oxide hydrate).
  • Oxidation of magnesium (burning):

    2\,\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\,\mathrm{MgO}
  • Magnesium oxide in water shows basicity (litmus test indicates alkaline): blue litmus remains blue or turns blue; red litmus turns blue.
  • Elements: Presently 118118 elements are known.