9th Class Chemistry Chapter 8 Notes explain the classification of elements based on conductivity, covering metals, non-metals, and metalloids. This chapter also discusses physical and chemical properties, electropositive character, and practical uses of common metals like sodium, calcium, silver, and gold.
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These 9th Class Chemistry Chapter 8 Notes follow the latest Punjab Board syllabus, making them ideal for matric students preparing for their annual exams. Every concept is explained with definitions, examples, and reactions for easy understanding.
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Classification of Element
According to their conductivity, elements are classified into three categories:
- Metals: Fe, Na, Mg, Ag, Au, etc.
- Non-metals: H, He, C, N, O, S, P, etc.
- Metalloids: Si, Ge, etc.
Physical Properties of Metals
Metals share several common physical properties:
- Almost all metals are solids, except mercury.
- They have high melting and boiling points.
- They possess metallic luster and can be polished.
- They are malleable and ductile, and give off a tone when hit.
- They are good conductors of heat and electricity.
- They have high density.
- All metals are hard except sodium and potassium.
Chemical Properties of Metals
Metals also share key chemical behaviors:
- All metals easily lose electrons and form positive ions.
- They readily react with oxygen to form basic oxides.
- They usually form ionic compounds with non-metals.
- They have metallic bonding.
Electropositive Character
Metals have the tendency to lose their valence electrons. This characteristic property is called electropositivity or metallic character.
Position in the Periodic Table
- Metals: Occupy the upper left position.
- Non-metals: Occupy the upper right positions.
- Metalloids: Occupy the central position.
Trends in Metallic Character
- Metallic character decreases across a period from left to right due to increasing nuclear charge.
- Metallic character increases down a group as atomic size increases.
This section of 9th Class Chemistry Chapter 8 Notes explains why sodium is more metallic than elements to its right, and why potassium is more reactive than sodium.
Electropositivity and Ionization Energy
Electropositive character depends on ionization energy, which depends on the size and nuclear charge of the atom. Small atoms with high nuclear charge have high ionization energy, making them less electropositive.
Why Sodium is More Reactive Than Magnesium
Sodium has one electron in its valence shell, a large atomic size, and low ionization energy, making it easy to lose an electron. Magnesium has two valence electrons and a smaller atomic size with higher ionization energy, making its second electron much harder to remove.
Group 1 Metals and Reactivity
Group 1 (alkali metals) are highly reactive because they can easily lose one electron to form a positive ion.
Example: Na → Na⁺ + e⁻
Properties of Sodium
- Silvery white with metallic luster; very soft and can be cut with a knife.
- Very malleable and ductile.
- Good conductor of heat and electricity.
- Burns in air with a golden yellow flame.
- Melting point: 97°C; boiling point: 883°C.
Uses of Sodium
- Sodium-potassium alloy is used as a coolant in nuclear reactors.
- It is used to produce yellow light in sodium vapor lamps.
- It is used as a reducing agent in the extraction of metals like titanium.
Uses of Other Common Metals
Calcium
- Used to remove sulphur from petroleum products.
- Used as a reducing agent to produce chromium, uranium, and zirconium.
Magnesium
- Used in flashlights and fireworks.
- Used in manufacturing light alloys.
- Magnesium ribbon is used in the Thermite Process.
- Used as an anode for corrosion prevention.
Silver
Silver is a white lustrous metal, an excellent conductor of heat and electricity, and highly ductile and malleable.
Uses: Photographic films, dental preparations, coins, silverware, ornaments, and mirror industries.
Gold
Gold is a yellow, soft, and highly malleable metal. It is very non-reactive, unaffected by atmosphere or acids.
Uses: Ornamental jewelry and coin-making due to its inertness and malleability.
Platinum
Platinum is resistant to tarnish and chemical attack, though soluble in hydrochloric and nitric acid.
Uses: Jewelry, catalytic converters in automobiles, hard disk drive coatings, fiber optic cables, and LCD manufacturing.
This practical section of 9th Class Chemistry Chapter 8 Notes is useful for understanding how metal properties translate into real-world industrial applications.
Non-Metals
Non-metals form negative ions (anions) by gaining electrons, making them electronegative in nature. They form acidic oxides.
Examples: Carbon, phosphorus, sulphur, and halogens.
Physical Properties of Non-Metals
- Solid non-metals are brittle and break easily.
- They are non-conductors of heat and electricity, except graphite.
- They are dull, except iodine, which is lustrous.
- They are generally soft, except diamond.
- They have low melting and boiling points, except silicon, graphite, and diamond.
- They have low densities.
Halogens and Their Reactions
Oxidizing Properties of Halogens
All halogens act as oxidizing agents. Fluorine is the strongest oxidizing agent, while iodine is the mildest.
- Fluorine oxidizes chloride ions: F₂ + 2KCl → 2KF + Cl₂
- Chlorine displaces bromide and iodide ions from their salts.
- Bromine displaces iodine from potassium iodide.
Reaction of Chlorine with Water
Chlorine reacts with water in the presence of sunlight to form hydrochloric acid and hypochlorous acid.
Cl₂ + H₂O → HCl + HOCl
Reaction of Bromine with Water
Bromine reacts with water in sunlight to form hydrobromic acid and hypobromous acid.
Br₂ + H₂O → HBr + HOBr
Reaction of Chlorine with Sodium Hydroxide
- With cold dilute NaOH: 2NaOH + Cl₂ → NaCl + NaOCl + H₂O
- With hot concentrated NaOH: 6NaOH + 3Cl₂ → 5NaCl + NaClO₃ + 3H₂O
This section of 9th Class Chemistry Chapter 8 Notes is essential for understanding halogen reactivity trends tested in board exams.
Practical Applications from the Chapter
9th Class Chemistry Chapter 8 Notes also cover interesting daily-life chemistry:
- Ice cream preparation: A mixture of ammonium nitrate, ammonium chloride, and ice creates an endothermic reaction that lowers temperature, keeping the ice cream at freezing point.
- Refrigerator cooling: A gas is liquefied inside a refrigerator to produce intense cooling.
- Heating copper sulphate: Green copper sulphate loses its water of crystallization on heating, turning into black copper oxide.
- Common binary compound formation: CO forms when coal burns in limited air, while CO₂ forms with abundant air supply.
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Why These Notes Matter for Exam Preparation
9th Class Chemistry Chapter 8 Notes are designed to cover both conceptual and practical portions of the chapter. Students should focus on:
- Classification of elements into metals, non-metals, and metalloids
- Physical and chemical properties of metals and non-metals
- Electropositivity trends and their relationship with ionization energy
- Uses of common metals like sodium, calcium, silver, gold, and platinum
- Halogen reactions with water and sodium hydroxide
Consistent revision of these 9th Class Chemistry Chapter 8 Notes ensures better performance in both short-question and long-question sections of the Punjab Board exam.
FAQs
Q1: What topics are covered in 9th Class Chemistry Chapter 8 Notes?
These notes cover classification of elements into metals, non-metals, and metalloids, their physical and chemical properties, electropositivity, uses of common metals, and halogen reactions with water and sodium hydroxide.
Q2: What is the difference between metals and non-metals?
Metals lose electrons to form positive ions and are good conductors of heat and electricity. Non-metals gain electrons to form negative ions and are generally poor conductors, except for graphite.
Q3: Why is sodium more reactive than magnesium?
Sodium has one valence electron, a larger atomic size, and lower ionization energy, making it easier to lose an electron. Magnesium has two valence electrons and higher ionization energy, making it less reactive.
Q4: What are metalloids? Give examples.
Metalloids are elements that show properties of both metals and non-metals. They occupy the central position in the periodic table. Silicon and germanium are common examples of metalloids.
Q5: Which halogen is the strongest oxidizing agent?
Fluorine is the strongest oxidizing agent among halogens because of its small size and high electronegativity. It can oxidize other halide ions in solution, while iodine is the weakest oxidizing agent.
Q6: What are the main uses of gold and platinum?
Gold is used in jewelry and coins due to its inertness and malleability. Platinum is used in catalytic converters, jewelry, fiber optic cables, and LCD manufacturing because of its resistance to tarnish.