Metals and Non-metals (Class 10): Notes और MCQ Practice

आसान भाषा में:

इस chapter में हम elements को उनकी properties के आधार पर Metals और Non-metals में classify करते हैं। Metals electrons donate करके electropositive ions बनाते हैं और mainly basic oxides देते हैं। वहीं Non-metals electrons accept करके electronegative ions बनाते हैं और acidic oxides देते हैं। जब Metals और Non-metals react करते हैं, तो electron transfer से मजबूत Ionic Bonds बनते हैं!

Most Important Points & Definitions:

1. Amphoteric Oxides: वो metal oxides जो acid और base दोनों के साथ react करके salt और water बनाते हैं (e.g., Al2O3, ZnO).
2. Reactivity Series: Metals की reactivity का decreasing order:

K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au.

1. Ionic Compounds: Ions के बीच strong electrostatic force होता है। इनके melting और boiling points बहुत high होते हैं और ये सिर्फ molten या aqueous state में electricity conduct करते हैं (solid में नहीं).
2. Metallurgy terms:

• Roasting: Sulfide ores को excess air में heat करना (e.g., 2ZnS + 3O2 → 2ZnO + 2SO2).
• Calcination: Carbonate ores को limited air में heat करना (e.g., ZnCO3 → ZnO + CO2).

1. Thermite Reaction: Fe2O3 + 2Al → 2Fe + Al2O3 + Heat (Railway tracks जोड़ने के काम आता है).
2. Corrosion Prevention: Galvanisation (Zinc की परत चढ़ाना) और Alloys बनाना (e.g., Brass = Cu + Zn, Bronze = Cu + Sn).

2 Memory Tricks:

• Reactivity Series Mnemonic:

"Kedarnath Ca Maali Aloo Zara Pheeke Pakata Hai" (K, Na, Ca, Mg, Al, Zn, Fe, Pb, H).

• Calcination vs Roasting:

C for Calcination = Carbonate ores (in limited air).

2 Common Board-Exam Mistakes:

1. Solid Ionic Conductance: बच्चे लिख देते हैं कि ionic compounds solid state में electricity conduct करते हैं। याद रखें, solid में ions free नहीं होते, इसलिए electricity केवल molten या solution state में ही flow होती है!
2. Hydrogen gas with HNO3: Metals dilute acids के साथ react करके H2 gas देते हैं, लेकिन HNO3 (Nitric acid) के साथ H2 नहीं निकलती क्योंकि HNO3 एक strong oxidising agent है (Exceptions: Mg और Mn dilute HNO3 के साथ H2 देते हैं).

Metals and Non-metals: Class 10 NCERT Quick Study Notes

1. Chapter in Short

This chapter explores the materials that make up the physical world around us:

• Physical and Chemical Properties: How metals and non-metals look, feel, and react with oxygen, water, and acids.
• The Reactivity Series: A ranking of metals from most reactive (like Potassium) to least reactive (like Gold).
• Ionic Bonding: How metals give electrons to non-metals to form stable compounds (like common salt).
• Extraction of Metals (Metallurgy): How pure metals are obtained from rocks found in the earth's crust.
• Corrosion and Alloys: Why metals rust or tarnish and how mixing them creates stronger, rust-free mixtures.

2. Key Concepts Explained Simply

A. Physical Properties and Their Exceptions

Usually, metals are shiny (lustrous), hard, can be beaten into thin sheets (malleable), drawn into thin wires (ductile), ring when struck (sonorous), and conduct heat and electricity well. Non-metals are usually dull, brittle, and poor conductors.

Important Exceptions to remember for exams:

• Mercury (Hg): The only metal that is a liquid at room temperature (used in thermometers).
• Bromine (Br): The only non-metal that is a liquid at room temperature.
• Gallium (Ga) and Caesium (Cs): Metals with such low melting points that they melt on your palm.
• Iodine (I): A non-metal, but it is lustrous (shiny).
• Carbon (Diamond): A non-metal, but the hardest naturally occurring substance with a very high melting point.
• Carbon (Graphite): A non-metal, but a good conductor of electricity (used in pencil leads and batteries).
• Lithium (Li), Sodium (Na), Potassium (K): Alkali metals that are so soft they can be sliced with a knife, with low densities.

B. Chemical Reactions of Metals

1. Reaction with Oxygen:

• Metal + Oxygen → Metal oxide (generally basic).
• Example: 2Cu + O₂ → 2CuO (Black copper oxide).
• Amphoteric Oxides: Oxides that react with both acids and bases to produce salt and water (e.g., Aluminium oxide Al₂O₃, Zinc oxide ZnO).
• Sodium and Potassium react so vigorously with air and moisture that they catch fire; hence, they are kept stored under kerosene oil.

1. Reaction with Water:

• Metal + Water → Metal hydroxide + Hydrogen gas.
• Cold water: Sodium (Na), Potassium (K), Calcium (Ca). Calcium floats because hydrogen bubbles stick to its surface.
• Hot water: Magnesium (Mg) does not react with cold water; it reacts with hot water and floats.
• Steam only: Aluminium (Al), Iron (Fe), Zinc (Zn).
• No reaction with water at all: Lead (Pb), Copper (Cu), Silver (Ag), Gold (Au).

1. Reaction with Acids:

• Metal + Dilute Acid → Salt + Hydrogen gas (H₂).
• Special case: Dilute Nitric acid (HNO₃) does not release H₂ with most metals because it is a strong oxidising agent—it turns H₂ into water (H₂O) and reduces itself to nitrogen oxides. Only Magnesium (Mg) and Manganese (Mn) react with very dilute HNO₃ to give H₂ gas.

1. Aqua Regia:

• A freshly prepared mixture of concentrated Hydrochloric acid (HCl) and concentrated Nitric acid (HNO₃) in the ratio 3 : 1. It can dissolve noble metals like Gold and Platinum.

C. Reactivity Series

A vertical list of metals arranged in decreasing order of their reactivity:

• Top (Most Reactive): K > Na > Ca > Mg > Al
• Middle (Moderately Reactive): Zn > Fe > Pb > [H]
• Bottom (Least Reactive): Cu > Hg > Ag > Au

A more reactive metal displaces a less reactive metal from its salt solution (Displacement Reaction).

• Example: Fe + CuSO₄ (blue) → FeSO₄ (pale green) + Cu (reddish-brown).

D. How Metals and Non-Metals Combine (Ionic Bonds)

• Metals lose valence electrons to form positive ions (cations).
• Non-metals gain those electrons to form negative ions (anions).
• The strong electrostatic attraction between these oppositely charged ions forms an ionic compound (e.g., NaCl, MgCl₂).

Properties of Ionic Compounds:

• Physical nature: Solid and hard; brittle.
• Melting & Boiling points: Very high (large amount of energy is needed to break strong ionic bonds).
• Solubility: Soluble in water, insoluble in solvents like kerosene and petrol.
• Conduction of electricity: Do not conduct electricity in the solid state (ions are locked in place). They conduct electricity only in molten (melted) state or aqueous (dissolved in water) state because ions are free to move.

E. Extraction of Metals (Metallurgy)

• Ores at the bottom (Unreactive - Au, Ag, Cu): Often found in free state. Copper and Mercury sulphides are reduced just by heating.
• Cinnabar (HgS): 2HgS + 3O₂ + Heat → 2HgO + 2SO₂, then 2HgO + Heat → 2Hg + O₂.
• Ores in the middle (Zn, Fe, Pb): Found as carbonates or sulphides. They are first converted to oxides:
• Roasting: Heating sulphide ores strongly in the presence of excess air.
• 2ZnS + 3O₂ + Heat → 2ZnO + 2SO₂
• Calcination: Heating carbonate ores strongly in limited/no air.
• ZnCO₃ + Heat → ZnO + CO₂
• Reduction: The oxide is reduced to metal using Carbon (C) or a more reactive metal (Thermite reaction):
• ZnO + C → Zn + CO
• Fe₂O₃ + 2Al → 2Fe (molten) + Al₂O₃ + Heat (Used to weld railway tracks).
• Ores at the top (Na, Ca, Mg, Al): Extracted by electrolytic reduction of their molten chlorides/oxides because carbon cannot pull oxygen away from these highly reactive metals.
• At Cathode (negative electrode): Metal is deposited (Na⁺ + e⁻ → Na).
• At Anode (positive electrode): Gas is released (2Cl⁻ → Cl₂ + 2e⁻).

F. Electrolytic Refining of Copper

• Anode: Thick block of impure copper.
• Cathode: Thin strip of pure copper.
• Electrolyte: Acidified Copper Sulphate (CuSO₄) solution.
• When current passes, pure copper from the anode dissolves and deposits onto the cathode. Insoluble impurities settle at the bottom as anode mud.

G. Corrosion and Prevention

• Rusting of Iron: Requires both oxygen (air) and moisture (water).
• Prevention methods:
• Painting, greasing, oiling.
• Galvanisation: Coating iron/steel with a thin layer of Zinc.
• Alloying: A homogeneous mixture of two or more metals, or a metal and a non-metal.
• Steel: Iron + Carbon (0.05% makes iron hard and strong).
• Stainless Steel: Iron + Nickel + Chromium (does not rust).
• Brass: Copper + Zinc (Cu + Zn).
• Bronze: Copper + Tin (Cu + Sn).
• Solder: Lead + Tin (Pb + Sn; has a low melting point, used to join electric wires).
• Amalgam: Any alloy that contains Mercury.
• Pure gold is 24 carat (too soft). In India, 22 carat gold (22 parts gold + 2 parts copper/silver) is used for making jewellery.

3. Important Definitions, Reactions, and Facts

• Malleability: The property of metals that allows them to be beaten into thin sheets (Gold and Silver are most malleable).
• Ductility: The ability of metals to be drawn into thin wires (1 gram of gold can form a wire 2 km long).
• Amphoteric Oxide: A metal oxide that reacts with both acids and bases to produce salt and water.
• Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
• Al₂O₃ + 2NaOH → 2NaAlO₂ (Sodium aluminate) + H₂O
• Gangue: Unwanted earthy impurities (sand, soil, clay) present in mined ore.
• Roasting: Converting sulphide ores into oxides by heating strongly in the presence of excess air.
• Calcination: Converting carbonate ores into oxides by heating strongly in limited air.
• Anodising: Creating a thick, protective oxide layer on aluminium using electrolysis to prevent corrosion.
• Aqua Regia: Ratio of 3 parts concentrated HCl to 1 part concentrated HNO₃.

4. Solved Board-Exam Style Questions

Question 1

What are amphoteric oxides? Choose the amphoteric oxides from the following and write a balanced equation showing its reaction with a base:

Na₂O, Al₂O₃, CO₂, ZnO

Answer:

Amphoteric oxides are metal oxides that react with both acids and bases to give salt and water.

• From the list, Al₂O₃ and ZnO are amphoteric oxides.
• Reaction with a base:

Al₂O₃ + 2NaOH → 2NaAlO₂ (Sodium aluminate) + H₂O

Question 2

Give reasons for the following:

(a) Sodium and Potassium are stored under kerosene oil.

(b) Ionic compounds have high melting and boiling points.

(c) Aluminium is a reactive metal, yet it is widely used to make cooking utensils.

Answer:

• (a) Sodium and Potassium react violently with oxygen and moisture present in the air, catching fire. To prevent accidental fires and cut off contact with air/moisture, they are stored under kerosene.
• (b) Ionic compounds consist of positively and negatively charged ions held together by very strong electrostatic forces of attraction. A large amount of heat energy is required to break these strong bonds.
• (c) When aluminium reacts with oxygen in air, it forms a thin, tough, and stable protective layer of aluminium oxide (Al₂O₃) on its surface. This layer prevents further reaction or corrosion. Additionally, aluminium is lightweight and a good conductor of heat.

Question 3

Differentiate between Roasting and Calcination with one chemical equation for each.

Answer:

Feature — Roasting — Calcination

Ore type — Used for Sulphide ores — Used for Carbonate ores

Air supply — Carried out in excess air — Carried out in limited or no air

Gas produced — Releases Sulphur dioxide (SO₂) — Releases Carbon dioxide (CO₂)

Chemical Equation — 2ZnS + 3O₂ + Heat → 2ZnO + 2SO₂ — ZnCO₃ + Heat → ZnO + CO₂

Question 4

An element 'X' reacts with oxygen to form an oxide with a high melting point. This oxide is soluble in water. Is 'X' likely to be (a) Calcium, (b) Carbon, (c) Silicon, or (d) Iron? Explain your choice.

Answer:

• Correct element: (a) Calcium.
• Explanation: Calcium is a metal that combines with oxygen to form Calcium oxide (CaO), an ionic compound with a high melting point. Calcium oxide dissolves in water to form Calcium hydroxide (slaked lime):

CaO + H₂O → Ca(OH)₂

Carbon forms a gas (CO₂), Silicon dioxide is insoluble in water, and Iron oxide is insoluble in water.

5. Common Mistakes and Quick Revision Points

• Don't confuse Roasting and Calcination: Remember Calcination is for Carbonates. Roasting is for Sulphides.
• Nitric Acid Trap: Students often write that metals produce H₂ gas with all acids. Remember: HNO₃ does NOT give H₂ gas with most metals. Only Mg and Mn produce H₂ gas with very dilute HNO₃.
• Ionic Conduction: Ionic compounds never conduct electricity in solid form! They only conduct in molten state or aqueous solution because the ions become free to move.
• Iron Rusting Requirements: Dry air alone will not rust iron; boiled water without air will not rust iron. Rusting requires both air (oxygen) and water.
• Galvanised Article Protection: Even if the zinc coating on an iron object is scratched, the iron remains protected because zinc is more reactive than iron and oxidises preferentially.