**CHAPTER 3: METALS AND NON-METALS**
**3.1 PHYSICAL PROPERTIES OF METALS**
**Metallic Lustre** • Pure metals have a shining/lustrous surface when cleaned | This property is called metallic lustre and distinguishes metals visually
**Malleability** • Definition: Ability of metals to be beaten into thin sheets without breaking | Examples: Gold and silver are most malleable metals | Cause: Metal atoms can slide past each other while maintaining metallic bonding
**Ductility** • Definition: Ability of metals to be drawn into thin wires | Gold is the most ductile metal—1 gram of gold can produce 2 km of wire | Wires in homes are made of ductile metals like copper
**Hardness** • Most metals are hard (resistance to scratching/deformation) | Hardness varies from metal to metal | Exception: Alkali metals (lithium, sodium, potassium) are very soft and can be cut with a knife
**Thermal Conductivity** • Definition: Ability to conduct and transfer heat | ALL metals are good conductors of heat | Best conductors: Silver and copper | Poor conductors: Lead and mercury | High melting points: Most metals melt only at very high temperatures
**Electrical Conductivity** • ALL metals are good conductors of electricity | Electrons in metal lattice move freely, allowing current flow | Why electric wires are coated with PVC/rubber: These are insulators that prevent electric shock
**Sonority** • Definition: Ability to produce sound when struck against hard surfaces | Metals are sonorous → school bells made of metal | Distinct metallic ring/ringing sound
**State of Matter** • Almost all metals are solids at room temperature (25°C) | Exception: Mercury is liquid at room temperature (melting point = –39°C)
**IMPORTANT EXCEPTIONS TO REMEMBER** • Gallium and caesium: Alkali metals with very low melting points (melt on palm heat) | Alkali metals: Soft, low density, low melting points, can be cut with knife | Mercury: Liquid metal at room temperature
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**3.1.2 PHYSICAL PROPERTIES OF NON-METALS**
**Definition** • Non-metals: Elements that lack properties characteristic of metals
**General Physical Properties** • Poor conductors of electricity (except graphite) | Poor conductors of heat (except diamond to some extent) | Not malleable (brittle—break when hammered) | Not ductile (cannot be drawn into wires) | Generally not lustrous (dull appearance) | Not sonorous (do not produce sound when struck) | Exception: Iodine is lustrous (shiny) despite being non-metal
**State of Matter** • Most exist as solids or gases at room temperature | Only exception: Bromine is a liquid non-metal at room temperature (boiling point = 58.8°C)
**Special Case: Carbon and Its Allotropes** • Definition: Allotropes are different forms of the same element with different properties | Diamond (allotrope of carbon): Hardest natural substance, high melting point, poor electricity conductor | Graphite (allotrope of carbon): Good conductor of electricity (only non-metal that conducts), soft, used in pencils and electrodes | Both are forms of solid carbon but have completely different properties
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**3.2 CHEMICAL PROPERTIES OF METALS**
**Key Principle** • Chemical properties more clearly distinguish metals from non-metals than physical properties do | Metals are generally reducing agents (lose electrons easily) | Non-metals are generally oxidizing agents (gain electrons)
**3.2.1 METALS BURNING IN AIR (COMBUSTION)**
**General Reaction Pattern** • Metals + Oxygen (in air) → Metal Oxides + Heat + Light
**Specific Examples with Equations**
• **Magnesium**: 2Mg + O₂ → 2MgO (dazzling white flame, rapid combustion)
• **Sodium**: 4Na + O₂ → 2Na₂O (burns with yellow/orange flame, very vigorous)
• **Copper**: 2Cu + O₂ → 2CuO (when heated, forms black copper oxide)
• **Iron**: 3Fe + 2O₂ → Fe₃O₄ (when heated strongly, forms ferroferric oxide—black powder)
• **Zinc**: 2Zn + O₂ → 2ZnO (burns with bluish-white flame)
• **Lead**: 2Pb + O₂ → 2PbO (burns less vigorously)
**Reactivity Order (Decreasing)** • Very reactive: Na, K, Mg (burn readily in air with flame) | Moderately reactive: Al, Zn, Fe (burn when heated strongly) | Less reactive: Cu, Pb (burn with difficulty, need strong heating) | Don't Confuse: Reactivity with flame color—different metals produce different colored flames
**Oxygen Supply Effect** • Limited oxygen → Incomplete combustion (may form oxides with different oxygen ratios) | Excess oxygen → Complete combustion to highest oxide
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**3.2.2 METAL OXIDES ARE BASIC**
**General Property** • Metal oxides are basic in nature (alkaline) | When dissolved in water, they form bases
**Equation Format**: Metal Oxide + Water → Metal Hydroxide (Base)
**Examples**:
• **Sodium oxide**: Na₂O + H₂O → 2NaOH (sodium hydroxide—strong base)
• **Magnesium oxide**: MgO + H₂O → Mg(OH)₂ (magnesium hydroxide—base)
• **Calcium oxide**: CaO + H₂O → Ca(OH)₂ (calcium hydroxide—base)
**Litmus Test** • Metal oxide solutions turn blue litmus paper RED → FALSE (they turn red litmus BLUE) | This proves basic/alkaline nature
**Why Basic?** • Metal oxides contain metal cations bonded to oxide ions (O²⁻) | Oxide ions react with water to form hydroxide ions (OH⁻), making solution basic
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**3.2.3 NON-METAL OXIDES ARE ACIDIC**
**General Property** • Non-metal oxides are acidic in nature | When dissolved in water, they form acids
**Equation Format**: Non-metal Oxide + Water → Acid
**Examples**:
• **Sulphur dioxide**: SO₂ + H₂O → H₂SO₃ (sulphurous acid)
• **Carbon dioxide**: CO₂ + H₂O → H₂CO₃ (carbonic acid)
• **Nitrogen dioxide**: 2NO₂ + H₂O → HNO₃ + HNO₂ (nitric and nitrous acids)
• **Phosphorus pentoxide**: P₂O₅ + 3H₂O → 2H₃PO₄ (phosphoric acid)
**Litmus Test** • Non-metal oxide solutions turn blue litmus paper RED | This proves acidic nature
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**COMPARISON: METAL OXIDES vs NON-METAL OXIDES**
| Property | Metal Oxides | Non-metal Oxides |
|---|---|---|
| Nature | Basic/Alkaline | Acidic |
| Litmus Change | Blue litmus stays blue; Red litmus → Blue | Blue litmus → Red; Red litmus stays red |
| With Water | Form bases/hydroxides | Form acids |
| Example | Na₂O, MgO, CaO | CO₂, SO₂, NO₂ |
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**DON'T CONFUSE** • Metal oxides with metal hydroxides: Both are basic but formed differently (oxide + water vs metal + base) | Acidic oxide with acidic metal: Oxides of non-metals are acidic; some metals form acidic oxides (like chromium trioxide CrO₃)
**KEY DEFINITIONS**
• **Metallic Lustre**: Shining appearance of pure metals due to surface reflection of light
• **Malleable**: Property to be beaten into thin sheets without breaking
• **Ductile**: Property to be drawn into thin wires without breaking
• **Sonorous**: Property to produce sound when struck
• **Allotropes**: Different forms of the same element showing different chemical and physical properties
• **Basic Oxide**: Oxide that reacts with water to form a base (metal oxide)
• **Acidic Oxide**: Oxide that reacts with water to form an acid (non-metal oxide)
Q1. A student observes that when a copper wire is heated at one end while holding the other end with bare hands, the hand feels hot after a few seconds. Which property of metals does this observation demonstrate?
Answer: A — The heat traveling from the heated end to the unheated end demonstrates thermal conductivity; students often confuse this with melting point or mechanical properties like malleability.
Q2. In a school laboratory, a student needs to make a long thin wire from a metal sample. Which property of metals should the teacher recommend to use?
Answer: A — Ductility is the ability to be drawn into wires; malleability is for beating into sheets, not stretching into wires.
Q3. Assertion (A): Mercury is a metal that exists as a liquid at room temperature. Reason (R): All metals have high melting points. Choose the correct option:
Answer: C — Mercury is indeed a liquid metal at room temperature, but this contradicts the reason that all metals have high melting points; the assertion is true but the reason is false.
Q4. A household electrical wire has copper conductor wrapped with plastic coating. Based on properties of metals and non-metals, explain why copper is used for the conductor part.
Answer: A — Copper conducts electricity while the non-metal plastic insulator prevents electric shock; students often confuse this with aesthetic or mechanical properties.
Q5. In Activity 3.7, when sulphur powder is burned and the fumes are collected in water, the resulting solution turns blue litmus paper red. What does this indicate about non-metals?
Answer: A — Burning sulphur produces SO₂ which forms acidic H₂SO₃ in water; students may confuse this with metals which typically form basic oxides.
Q6. Assertion (A): Diamond and graphite have different physical properties despite both being forms of carbon. Reason (R): Physical properties depend on the arrangement of atoms in the substance. Choose the correct option:
Answer: A — Different atomic arrangements create allotropes with distinct properties; the reason directly explains why diamond (hard, insulator) and graphite (soft, conductor) differ.
Q7. A student strikes a metal with a hammer and observes that the metal bends rather than breaks. Another student burns the same metal and observes that the oxide formed is basic. Which two properties are being demonstrated here?
Answer: A — Bending without breaking shows malleability (physical property); basic oxide formation is a characteristic chemical property of metals.
Q8. Assertion (A): Iodine is a non-metal with a lustrous surface. Reason (R): All substances with metallic lustre are metals. Choose the correct option:
Answer: C — Iodine is indeed a non-metal with lustre, contradicting the reason that lustre indicates a metal; physical properties alone cannot classify elements.
Q9. In an experiment, a student tests the electrical conductivity of coal (carbon) and copper using the circuit in Fig. 3.2. The bulb glows only when copper is placed between terminals A and B. What can be concluded?
Answer: A — Copper's conductivity confirms metals conduct electricity while carbon (non-metal) does not; students may incorrectly assume all non-metals are non-conductors, but graphite is an exception.
Q10. A student attempts to cut sodium metal with a knife and finds it very soft and cuts easily. Why is sodium metal not used for making cooking vessels despite being a metal?
Answer: A — Sodium's softness and low melting point make it unsuitable for cookware; students may focus on electrical or optical properties rather than mechanical strength.
What is metallic lustre?
The shining or lustrous appearance of pure metals due to their atomic structure.
Define malleability.
The property of metals that allows them to be beaten into thin sheets without breaking.
What is ductility in metals?
The ability of metals to be drawn into long, thin wires without breaking.
Why are copper and aluminium used for cooking vessels?
Because they are good conductors of heat and have high melting points.
Name the most ductile metal.
Gold is the most ductile metal; 1 gram can produce a wire of about 2 km length.
What do we mean by sonority in metals?
The property of metals to produce a sound when struck against a hard surface.
Why are electric wires coated with PVC or rubber?
PVC and rubber are non-conductors of electricity and insulate the wire to prevent electric shock.
What are allotropes of carbon?
Different forms of carbon element such as diamond, graphite, and coal with different properties.
Which non-metal is lustrous?
Iodine is a non-metal that has a lustrous or shining appearance.
What oxides do metals form when burnt in air?
Metals form basic (alkaline) oxides when burnt in air, which dissolve in water to give basic solutions.
Give one example each of a metal which (i) is liquid at room temperature, (ii) can be easily cut with a knife, (iii) is the best conductor of heat. [2 marks]
Recall specific metal examples: liquid metal at room temperature = Mercury; soft metal that can be cut = Sodium (or potassium, lithium); best heat conductor = Silver (or copper).
Explain why iodine is classified as a non-metal even though it has a lustrous appearance. What does this tell us about classifying elements based on physical properties alone? [3 marks]
Iodine's lustre is an exception to physical property rules; classification must rely on chemical properties (iodine forms acidic oxides). Physical properties have too many exceptions (diamond hardness, graphite conductivity, mercury liquid state, alkali metals softness).
When magnesium ribbon is burnt, it forms magnesium oxide. When sulphur powder is burnt, it forms sulphur dioxide. Explain why magnesium oxide is basic while sulphur dioxide is acidic. What does this difference reveal about the chemical nature of metals versus non-metals? Support your answer with the behaviour of their oxides in water. [5 marks]
Metals lose electrons and form basic oxides (MgO + H₂O → Mg(OH)₂, basic); non-metals gain electrons and form acidic oxides (SO₂ + H₂O → H₂SO₃, acidic). This reflects fundamental difference in electron behaviour: metals are electron donors, non-metals are electron acceptors. Chemical classification is more reliable than physical properties.
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