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By Shailendra Singh
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Updated on 11 Nov 2025, 18:20 IST
Scientists have discovered over 118 elements, which are broadly classified into metals, non-metals, and metalloids. Understanding the properties and behavior of these elements is fundamental to chemistry and has numerous practical applications in our daily lives.
Metals are electropositive elements that are typically hard, sonorous, malleable, ductile, with high tensile strength and excellent conductivity of heat and electricity. Non-metals exhibit properties opposite to metals, while metalloids show characteristics of both.
Understanding the physical differences between metals and non-metals helps identify and classify elements effectively.
| Property | Metals | Non-Metals |
| Physical State | Solids at room temperature (Exception: Mercury is liquid) | Gases or solids (Exception: Bromine is liquid) |
| Appearance | Shiny, lustrous surface | Dull surfaces (Exception: Diamond, Iodine crystals have lustre) |
| Hardness | Generally hard (Exception: Sodium and potassium are soft) | Generally soft (Exception: Diamond is extremely hard) |
| Malleability | Can be beaten into thin sheets (e.g., aluminium foil) | Brittle, break easily when hammered |
| Ductility | Can be drawn into wires (e.g., copper wires) | Cannot be drawn into wires |
| Sonority | Produce sound when struck (e.g., tin cry) | Do not produce sound |
| Conductivity | Good conductors of heat and electricity (Exception: Lead for heat, Mercury for electricity) | Poor conductors (Exception: Graphite conducts electricity) |
| Melting & Boiling Points | Generally high | Generally low (Exception: Diamond) |
| Density | High density, heavy | Lower density |
| Valency | 1 to 3 electrons in outermost shell | 4 to 8 electrons in outermost shell |
| Nature | Electropositive - tend to lose electrons | Electronegative - tend to gain electrons |
Metals:
Non-Metals:
Almost all metals combine with oxygen to form metal oxides, which are generally basic in nature.
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General Reaction:
Metal + Oxygen → Metal Oxide
Specific Examples:
| Metal | Reaction | Observation |
| Sodium | 4Na + O₂ → 2Na₂O | Burns with golden yellow flame |
| Potassium | 4K + O₂ → 2K₂O | Burns with pink-violet flame |
| Magnesium | 2Mg + O₂ → 2MgO | Burns with brilliant white light (needs heating) |
| Aluminium | 4Al + 3O₂ → 2Al₂O₃ | Forms protective oxide layer |
| Zinc | 2Zn + O₂ → 2ZnO | Forms protective oxide layer |
| Iron | 3Fe + 2O₂ → Fe₃O₄ | Iron filings burn vigorously when sprinkled in flame |
| Copper | 2Cu + O₂ → 2CuO | Forms black copper oxide |
Amphoteric Oxides: Some metal oxides like Al₂O₃ and ZnO are amphoteric - they react with both acids and bases:

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (reaction with acid)Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (reaction with base)
Reactivity Order with Oxygen: Na > Mg > Zn > Fe > Cu

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Important Process - Anodising: Anodising forms a thick protective oxide layer on aluminium. The clean aluminium article is made the anode and electrolysed with dilute H₂SO₄. The oxygen evolved at the anode reacts with aluminium to create a thicker protective layer that can be dyed for attractive finishes.
Metals react with water to produce metal oxides (or hydroxides) and hydrogen gas. The reactivity varies significantly:
General Reactions:
Metal + Water → Metal Oxide + HydrogenMetal Oxide + Water → Metal Hydroxide

Reactivity Categories:
| Reactivity | Metals | Reaction Type | Example |
| Very Reactive | K, Na | React violently with cold water; hydrogen catches fire | 2Na + 2H₂O → 2NaOH + H₂ + heat |
| Moderately Reactive | Ca | Reacts with cold water; no fire | Ca + 2H₂O → Ca(OH)₂ + H₂ |
| Less Reactive | Mg | Reacts with hot water | Mg + 2H₂O → Mg(OH)₂ + H₂ |
| Low Reactivity | Al, Zn, Fe | React only with steam | 2Al + 3H₂O → Al₂O₃ + 3H₂ |
| No Reaction | Cu, Ag, Au | Do not react with water | No reaction |
Reactivity Order with Water: K > Na > Ca > Mg > Zn > Fe > Cu
Safety Note: Sodium and potassium are kept in kerosene to prevent contact with moisture in air, which would cause violent reactions.
Metals react with dilute acids to form metal salts and release hydrogen gas. The metal replaces hydrogen atoms in the acid.
General Reaction:
Metal + Dilute Acid → Metal Salt + Hydrogen
Specific Examples:
Mg + 2HCl → MgCl₂ + H₂↑Zn + 2HCl → ZnCl₂ + H₂↑Fe + 2HCl → FeCl₂ + H₂↑Cu + HCl → No reaction
Reactivity Order with Acids: Na > Mg > Zn > Fe > Cu
Important Notes:
Au + 3Cl → AuCl₃ (in aqua regia)Pt + 4Cl → PtCl₄ (in aqua regia)
Metals combine with chlorine to form ionic chlorides (electrovalent compounds):
2Na + Cl₂ → 2NaClCa + Cl₂ → CaCl₂Mg + Cl₂ → MgCl₂Zn + Cl₂ → ZnCl₂
During these reactions:
Only a few reactive metals form ionic hydrides by reacting with hydrogen:
2Na + H₂ → 2NaH (Sodium hydride)2K + H₂ → 2KH (Potassium hydride)Ca + H₂ → CaH₂ (Calcium hydride)
Most metals don't form hydrogen compounds as metals lose electrons while hydrogen typically shares or loses electrons rather than accepting them.
The Activity Series (or Reactivity Series) arranges metals in decreasing order of their chemical reactivity. This series is fundamental for predicting chemical reactions.
Most Reactive (Top)↓Potassium (K)Sodium (Na)Barium (Ba)Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Nickel (Ni)Tin (Sn)Lead (Pb)[HYDROGEN (H)] ← Reference pointCopper (Cu)Mercury (Hg)Silver (Ag)Gold (Au)Platinum (Pt)↓Least Reactive (Bottom)
The reactivity series is established through various experimental observations:
Displacement Reaction Example:
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)(More reactive) (Less reactive displaced)
The blue color of copper sulfate fades as zinc displaces copper, demonstrating zinc's higher reactivity.
Mg + H₂SO₄ → MgSO₄ + H₂ Zn + H₂SO₄ → ZnSO₄ + H₂
Fe + CuSO₄ → FeSO₄ + Cu (Iron is more electropositive than copper)
Free State (Native Metals): Metals that remain unaffected by moisture, oxygen, and CO₂ occur in native form:
Combined State: Reactive metals occur as compounds in minerals:
Mineral: Metal-bearing substances naturally occurring in the earth's crust
Ore: Minerals from which metals can be extracted profitably and economically
Important Ores:
| Metal | Ore Name | Chemical Formula |
| Iron | Haematite | Fe₂O₃ |
| Iron | Magnetite | FeO·Fe₂O₃ |
| Iron | Iron Pyrites | FeS₂ |
| Aluminium | Bauxite | Al₂O₃·2H₂O |
| Copper | Copper Pyrites | CuFeS₂ |
| Zinc | Zinc Blende | ZnS |
| Zinc | Calamine | ZnCO₃ |
| Lead | Galena | PbS |
| Mercury | Cinnabar | HgS |
| Calcium | Limestone | CaCO₃ |
| Sodium | Rock Salt | NaCl |
| Silver | Horn Silver | AgCl |
Gangue (Matrix): Unwanted impurities like sand, clay, and rocky material present in ores
Metallurgy is the science of extracting metals from their ores and refining them for use.
Removal of gangue from ore using various methods:
A. Hydraulic Washing (Gravity Separation/Levigation)
B. Froth Floatation Process
C. Magnetic Separation
D. Leaching (Chemical Separation)
Al₂O₃ + 2NaOH + H₂O → 2NaAlO₂ + H₂O (Bauxite dissolves, Fe₂O₃ and silicates remain) 2NaAlO₂ + 2H₂O → Al(OH)₃↓ + NaOH (On dilution/CO₂ treatment) 2Al(OH)₃ --1473K-> Al₂O₃ + 3H₂O (On heating)
A. Calcination
Effects:
Examples:
ZnCO₃ → ZnO + CO₂(Calamine to Zinc oxide)Al₂O₃·2H₂O → Al₂O₃ + 2H₂O(Bauxite to Alumina)
B. Roasting
Effects:
Example:
2ZnS + 3O₂ → 2ZnO + 2SO₂
Both processes carried out in reverberatory furnace
A. For Metals Low in Reactivity Series (Cu, Hg, Ag)
Examples:
2HgO --Heat--> 2Hg + O₂2Cu₂S + 3O₂ --Heat--> 2Cu₂O + 2SO₂2Cu₂O + Cu₂S --Heat--> 6Cu + SO₂
B. For Metals in Middle of Reactivity Series (Zn, Fe, Pb, Ni, Sn)
(i) Carbon Reduction (Smelting):
ZnO + C → Zn + COSnO₂ + 2C → Sn + 2CO
Carbon monoxide also acts as reducing agent:
ZnO + CO → Zn + CO₂Fe₂O₃ + 3CO → 2Fe + 3CO₂
(ii) Hydrogen Reduction:
WO₃ + 3H₂ → W + 3H₂O
(iii) Aluminothermy:
Cr₂O₃ + 2Al → Al₂O₃ + 2Cr3MnO₂ + 4Al → 2Al₂O₃ + 3Mn
Thermite Reaction: Used for welding railway tracks
Fe₂O₃ + 2Al → 2Fe (molten) + Al₂O₃
C. For Highly Reactive Metals (Na, Ca, Mg, K, Al)
Electrolytic Reduction:
Sodium Extraction:
2NaCl --Electrolysis--> 2Na + Cl₂At Cathode: Na⁺ + e⁻ → NaAt Anode: 2Cl⁻ → Cl₂ + 2e⁻
Aluminium Extraction (Hall-Héroult Process):
At Cathode: Al³⁺ + 3e⁻ → Al(l)At Anode: 2O²⁻ → O₂ + 4e⁻ 2C + O₂ → 2CO 2CO + O₂ → 2CO₂
A. Distillation
B. Liquation
C. Oxidation Methods
(i) Bessemerisation: Using Bessemer converter
(ii) Cupellation: For metals containing impurities that form volatile oxides
(iii) Poling: For removing oxide impurities from crude metal
Cu₂O + CH₄ → 6Cu + 2H₂O + CO(Green wood poles release hydrocarbons)
D. Electrolytic Refining
At Anode: M → M^n+ + ne⁻At Cathode: M^n+ + ne⁻ → M (pure)
Anode mud: Less reactive impurities (Au, Ag in copper refining) Solution: More reactive impurities remain dissolved
E. Zone Refining
F. Vapor Phase Refining
(i) Mond Process (for Nickel):
Ni (impure) + 4CO -330-350K-> Ni(CO)₄ (vapor)Ni(CO)₄ --Heat~1700K--> Ni (pure) + 4CO
(ii) Van Arkel Method (for Ti, Zr):
Ti (impure) + 2I₂ --500K--> TiI₄ (vapor)TiI₄ --1700K--> Ti (pure) + 2I₂
Flux: Substance added during smelting to remove non-fusible impurities Slag: Fusible substance formed when flux combines with impurities
| Impurity Type | Flux | Slag Formed |
| Acidic (SiO₂, P₂O₅) | Basic (CaO) | CaSiO₃, Ca₃(PO₄)₂ |
| Basic (MnO) | Acidic (SiO₂) | MnSiO₃ |
Examples:
SiO₂ + CaO → CaSiO₃ (slag)P₂O₅ + 3CaO → Ca₃(PO₄)₂ (slag)MnO + SiO₂ → MnSiO₃ (slag)
Raw Materials:
Reactions in Blast Furnace:
Zone 1 (Lower region - 2200K):
C + O₂ → CO₂ + Heat
Zone 2 (Middle region - 1500K):
CO₂ + C → 2CO(Carbon monoxide - reducing agent)
Zone 3 (Upper region - 900K):
Fe₂O₃ + 3CO → 2Fe + 3CO₂(Iron oxide reduced to iron)
Slag Formation:
CaCO₃ → CaO + CO₂CaO + SiO₂ → CaSiO₃ (slag)(Removes silica impurities)
Product: Molten iron collected at bottom; slag floats on top
Types of Iron:
| Type | Carbon Content | Properties | Uses |
| Pig Iron | 2.5-4.0% | Hard, brittle, non-malleable | Raw material for steel |
| Wrought Iron | 0.1-0.25% | Soft, malleable, ductile | Welding, ornamental work |
| Steel | 0.1-1.7% | Hard, malleable, high tensile strength | Construction, machinery |
Ore: Bauxite (Al₂O₃·2H₂O)
Step 1: Baeyer's Process (Purification)
Al₂O₃·2H₂O + 2NaOH → 2NaAlO₂ + 3H₂O2NaAlO₂ + CO₂ + 3H₂O → 2Al(OH)₃ + Na₂CO₃2Al(OH)₃ --Heat 1473K--> Al₂O₃ + 3H₂O
Step 2: Hall-Héroult Process (Electrolysis)
At Cathode: Al³⁺ + 3e⁻ → AlAt Anode: 2O²⁻ → O₂ + 4e⁻ C + O₂ → CO₂
Why Cryolite:
Properties of Aluminium:
Uses of Aluminium:
Corrosion is the slow destruction of metals due to chemical reactions with oxygen, moisture, CO₂, SO₂, H₂S, and other atmospheric substances. It weakens metals progressively and can lead to complete destruction.
Electrochemical Process:
M → M⁺ + e⁻ (Metal loses electrons)
Rust = Hydrated iron(III) oxide [Fe₂O₃·xH₂O + Fe(OH)₃]
Essential Conditions:
Reaction:
Fe + H₂O + O₂ → Fe₂O₃·xH₂O + Fe(OH)₃(Iron) (Rust - reddish brown, flaky)
Factors Accelerating Corrosion:
Examples of Corrosion:
Painting:
Greasing/Oiling:
Coating with Enamel:
Process: Iron article dipped in molten zincResult: Zinc coating prevents rusting
Process:
Stainless Steel:
Example: Mg/Zn connected to Fe pipe Mg/Zn corrodes; Fe protected
Applications: Aircraft bodies, window frames, cookware
For Copper/Brass:
For Automobiles:
For Steel/Nuclear Plants:
Alloy: Homogeneous mixture of two or more metals, or a metal with a non-metal, where the major component is a metal.
Purpose of Alloying:
Amalgam: Special alloy containing mercury as one component
Methods:
Example: Silver and zinc (white) form pink alloy
1. Ferrous Alloys - Contain iron
2. Non-Ferrous Alloys - Do not contain iron
| Alloy | Composition | Uses |
| Duralumin | Al (95%), Cu (4%), Mg (0.5%), Mn (0.5%) | Aircraft parts, automobile parts, pressure cookers |
| Magnalium | Al (95%), Mg (5%) | Balance beams, light instruments, pressure cookers |
| Alloy | Composition | Uses |
| Brass | Cu (80%), Zn (20%) | Utensils, machinery parts, condenser tubes, wires |
| Bronze | Cu (90%), Sn (10%) | Statues, coins, utensils |
| Gun Metal | Cu (90%), Sn (10%) | Gun barrels |
| Bell Metal | Cu (80%), Sn (20%) | Bells and gongs |
| German Silver | Cu (60%), Zn (20%), Ni (20%) | Silver ware, resistance wires (no silver content!) |
| Phosphor Bronze | Cu (95%), Sn (4.8%), P (0.2%) | Springs, electrical switches |
| Monel Metal | Cu (30%), Ni (67%), Fe+Mn (3%) | Corrosion-resistant pumps, acid containers |
| Alloy | Composition | Uses |
| Coinage Silver | Ag (90%), Cu (10%) | Silver coins |
| Silver Solder | Ag (63%), Cu (30%), Zn (7%) | Soldering |
| Dental Alloy | Ag (33%), Hg (52%), Sn (12.5%), Cu (2%), Zn (0.5%) | Dental fillings |
| Alloy | Composition | Uses |
| Solder | Pb (50%), Sn (50%) | Soldering broken metal pieces |
| Type Metal | Pb (70%), Sb (20%), Sn (10%) | Printing type |
| Alloy | Composition | Uses |
| Stainless Steel | Fe (73%), Cr (18%), Ni (8%), C (1%) | Utensils, surgical instruments, watch cases, automobile parts |
| Nickel Steel | Fe (96-98%), Ni (2-4%) | Cables, automobile/aeroplane parts, armor plates |
| Chrome Steel | Fe (98%), Cr (2%) | Axles, ball bearings, cutting tools |
| Alnico | Fe (60%), Ni (20%), Al (12%), Co (8%) | Permanent magnets |
Steel: Alloy of iron and carbon (0.15-1.7% carbon)
Note: Electrical conductivity of alloys is generally less than pure metals.
Gold Alloys:
Pure gold too soft for jewelry; alloyed with copper/silver for hardness.
Magnetic Metals: Only iron, cobalt, nickel are naturally magnetic. Steel (mostly iron) is also magnetic.
Strategic Metals: Titanium, chromium, manganese, zirconium
Extreme Properties:
Properties:
Uses:
Properties:
Uses: Photography (light-sensitive films)
Properties:
Uses: Water softening
Properties:
CuSO₄·5H₂O --373K--> CuSO₄·H₂O --413K--> CuSO₄ --443K--> CuO + SO₂
Uses:
Atomic Number: 16
Atomic Mass: 32
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁴
Valencies: +2, +4, +6, -2
Occurrence:
Allotropy:
A. Crystalline Allotropes:
| Type | Structure | Stability | Other Names |
| Rhombic (α-sulphur) | S₈ distorted ring | Stable at room temp | - |
| Monoclinic (β-sulphur) | S₈ needle-shaped crystals | Stable above 368.6K | Prismatic sulphur |
Transition: Rhombic ⇌ Monoclinic at 368.6K (transition temperature)
B. Non-Crystalline Allotropes:
Uses:
Atomic Number: 15
Atomic Mass: 31
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p³
Valencies: +3, +5
Name Origin: Greek - phos (light) + phero (carry) = "light carrier"
Occurrence:
Allotropes:
| Type | Color | Structure | Properties |
| White/Yellow | White → Yellow | P₄ tetrahedral (P-P-P = 60°) | Highly reactive, poisonous, garlic smell, catches fire in air, kept in cold water |
| Red | Red | Complex chain (P-P-P = 100°) | Odorless, high ignition point, stable |
| Black | Black | Layered | Most stable, odorless |
| Violet/Purple | Violet | - | - |
Uses:
Structure: Bent molecule (allotrope of oxygen)
Properties:
Uses:
Environmental Importance: Ozone layer in stratosphere blocks harmful UV radiation from sun
Structure: H-O-O-H (non-linear)
Properties:
Uses:
PbS + 4H₂O₂ → PbSO₄ + 4H₂O (Yellow) → (White)
Structure: Pyramidal (N with 3 H atoms)
Uses:
Structure: O=N-OH with double-bonded O
Properties: Strong oxidizing agent
Uses:
Structure: O=S(=O)(OH)₂
Properties: Strong acid, called "King of Acids"
Uses:
Common Name: Acid of common salt
Uses:
Common Name: Nausadar
Uses:
Occurrence: Sand (most abundant form)
Uses:
| Formula Name | Chemical Representation | Explanation |
| Metal Oxidation | M → M^n+ + ne⁻ | Metal loses electrons to form positive ions |
| Ionic Bond Formation | M + X → M⁺X⁻ | Metal transfers electron(s) to non-metal |
| Metal with Oxygen | Metal + O₂ → Metal Oxide | Most metals form basic oxides |
| Sodium Burning | 4Na + O₂ → 2Na₂O | Golden yellow flame |
| Magnesium Burning | 2Mg + O₂ → 2MgO | Brilliant white light |
| Iron Oxidation | 3Fe + 2O₂ → Fe₃O₄ | Magnetic iron oxide |
| Amphoteric Oxide (Aluminium) | Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O | Reacts with acid |
| Amphoteric Oxide (Aluminium) | Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O | Reacts with base |
| Metal Hydroxide Formation | Metal Oxide + H₂O → Metal Hydroxide | Soluble oxides form hydroxides |
| Sodium with Water | 2Na + 2H₂O → 2NaOH + H₂ + heat | Violent reaction |
| Calcium with Water | Ca + 2H₂O → Ca(OH)₂ + H₂ | Less violent |
| Magnesium with Hot Water | Mg + 2H₂O → Mg(OH)₂ + H₂ | Reacts with hot water |
| Aluminium with Steam | 2Al + 3H₂O → Al₂O₃ + 3H₂ | Reacts only with steam |
| Metal with Acid | Metal + Acid → Salt + H₂ | General displacement reaction |
| Magnesium with HCl | Mg + 2HCl → MgCl₂ + H₂ | Rapid reaction |
| Zinc with HCl | Zn + 2HCl → ZnCl₂ + H₂ | Moderate reaction |
| Aqua Regia Formation | 3HCl + HNO₃ → NOCl + 2Cl + 2H₂O | Dissolves noble metals |
| Displacement Reaction | Zn + CuSO₄ → ZnSO₄ + Cu | More reactive displaces less reactive |
| Calcination (Zinc) | ZnCO₃ → ZnO + CO₂ | Heating in limited air |
| Calcination (Aluminium) | Al₂O₃·2H₂O → Al₂O₃ + 2H₂O | Removing water |
| Roasting (Zinc) | 2ZnS + 3O₂ → 2ZnO + 2SO₂ | Heating in excess air |
| Carbon Reduction | ZnO + C → Zn + CO | Smelting process |
| CO Reduction | Fe₂O₃ + 3CO → 2Fe + 3CO₂ | In blast furnace |
| Thermite Reaction | Fe₂O₃ + 2Al → 2Fe + Al₂O₃ | Aluminothermy, highly exothermic |
| Chromium Reduction | Cr₂O₃ + 2Al → 2Cr + Al₂O₃ | Using aluminium |
| Sodium Electrolysis | 2NaCl → 2Na + Cl₂ | Electrolysis of molten salt |
| Aluminium Electrolysis | 2Al₂O₃ → 4Al + 3O₂ | In molten cryolite |
| Slag Formation (Calcium) | CaO + SiO₂ → CaSiO₃ | Removes acidic impurities |
| Rusting | Fe + H₂O + O₂ → Fe₂O₃·xH₂O | Requires both oxygen and water |
| Hydrogen Peroxide Oxidation | PbS + 4H₂O₂ → PbSO₄ + 4H₂O | Cleaning paintings |
| Ammonia Synthesis | N₂ + 3H₂ → 2NH₃ | Haber process |
| Baeyer's Process Step 1 | Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O | Dissolving bauxite |
| Baeyer's Process Step 2 | 2NaAlO₂ + CO₂ + 3H₂O → 2Al(OH)₃ + Na₂CO₃ | Precipitation |
| Baeyer's Process Step 3 | 2Al(OH)₃ → Al₂O₃ + 3H₂O | Heating to get pure alumina |
Learn metals and non-metals is fundamental to chemistry and has immense practical significance. From the extraction of iron and aluminium that forms the backbone of modern infrastructure to preventing corrosion that saves billions in maintenance costs, these concepts directly impact our daily lives.
Chapter Important Notes:
Learn these concepts provides a strong foundation for advanced chemistry and practical applications in metallurgy, materials science, and engineering.
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Metals are typically solid, shiny elements that conduct heat and electricity well, are malleable (can be hammered into sheets), and ductile (can be drawn into wires). They tend to lose electrons and form positive ions (cations). Non-metals, on the other hand, are usually gases or brittle solids with dull surfaces. They are poor conductors of heat and electricity (except graphite), cannot be shaped easily, and tend to gain electrons to form negative ions (anions). Metals form basic oxides while non-metals form acidic or neutral oxides.
Mercury (Hg) is the only metal that exists in liquid state at room temperature. Due to this unique property, mercury is stored in iron bottles and has been historically used in thermometers and barometers, though its use is now limited due to toxicity concerns.
Sodium and potassium are highly reactive alkali metals that react vigorously with moisture and oxygen in the air. When exposed to moist air, they can catch fire spontaneously. To prevent this dangerous reaction, these metals are stored under kerosene oil, which acts as a barrier preventing contact with air and moisture.
Diamond, an allotropic form of carbon (a non-metal), is the hardest naturally occurring substance. Despite carbon being generally soft in its graphite form, diamond's unique crystalline structure makes it exceptionally hard, which is why it's used in cutting tools and industrial applications.
Metals react with dilute acids to produce metal salts and hydrogen gas because metals can donate electrons to hydrogen ions (H⁺) in the acid, allowing hydrogen gas to be released. Non-metals, however, are electron acceptors rather than electron donors, so they cannot supply electrons to H⁺ ions and therefore don't displace hydrogen from acids. For example, zinc reacts with hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂, but carbon or sulfur won't react with dilute acids.
When metals react with oxygen, they form metal oxides. This reaction varies in intensity depending on the metal's reactivity. Highly reactive metals like sodium and potassium catch fire when exposed to moist air and must be stored carefully. Moderately reactive metals like magnesium, aluminum, and zinc form protective oxide layers that prevent further oxidation. Less reactive metals like lead, silver, and gold don't react readily with oxygen even at high temperatures, which is why they're called noble metals.
Iron rusts when exposed to both moisture and oxygen, forming hydrated iron(III) oxide (Fe₂O₃·xH₂O), which is the reddish-brown flaky substance we see as rust. This process weakens the metal structure over time. Aluminum also reacts with oxygen, but it forms a thin, protective layer of aluminum oxide (Al₂O₃) on its surface that prevents further corrosion. This protective layer is so effective that aluminum appears resistant to corrosion despite being a reactive metal.
The reactivity series (also called activity series) is an arrangement of metals in order of their decreasing chemical reactivity, from most reactive (potassium) to least reactive (gold). The series helps predict how metals will behave in chemical reactions.
Applications include: determining which metals can displace others from salt solutions, predicting which metals will react with water or acids, and understanding which reduction methods are needed to extract metals from their ores. More reactive metals can displace less reactive metals from their compounds.
A mineral is any naturally occurring compound of a metal found in the Earth's crust. An ore is a specific type of mineral from which a metal can be extracted profitably and economically. For example, aluminum is found in both bauxite (Al₂O₃·2H₂O) and china clay (Al₂O₃·2SiO₂·2H₂O), but only bauxite is considered an ore of aluminum because extracting aluminum from it is commercially viable. All ores are minerals, but not all minerals are ores.
Aluminium is reactive but forms a thin protective layer of aluminium oxide (Al₂O₃) that prevents further oxidation, making it corrosion-resistant.
Sodium is extremely reactive and catches fire when exposed to moist air. Kerosene prevents contact with oxygen and moisture, keeping sodium safe.
Carbonate and sulfide ores are converted to oxides through calcination (for carbonates) or roasting (for sulfides) because it's much easier to extract metals from their oxides than from carbonates or sulfides. Metal oxides can be reduced using carbon, hydrogen, or other reducing agents more efficiently. For example, zinc carbonate (ZnCO₃) is heated to convert it to zinc oxide (ZnO), which can then be reduced with carbon to obtain metallic zinc.
Electrolytic refining is a purification process where impure metal acts as the anode and a pure metal strip acts as the cathode, both suspended in a solution of the metal's salt (electrolyte).
When electric current passes through, metal from the impure anode dissolves into the electrolyte and pure metal deposits on the cathode. Impurities either remain in solution or collect as anode mud at the bottom. This method is used to refine copper, gold, silver, lead, zinc, and aluminum, producing metals of very high purity.
Corrosion is the slow destruction of metals due to chemical reactions with oxygen, carbon dioxide, moisture, sulfur dioxide, hydrogen sulfide, and other substances in the atmosphere. During corrosion, metal atoms lose electrons (oxidation) and convert into ions, forming compounds like oxides, carbonates, or sulfides on the metal surface. The process requires both oxygen and moisture neither alone can cause corrosion. Factors that speed up corrosion include contact with more reactive metals, presence of pollutants in air, and exposure to acids or salts.
Rusting of iron can be prevented through several methods:
Anodising is a process of forming a thick, protective oxide layer on aluminum. During anodising, clean aluminum is made the anode in an electrolytic cell with dilute sulfuric acid. Oxygen gas evolved at the anode reacts with aluminum to create a thicker protective oxide layer than would form naturally.
This oxide layer can be dyed to give aluminum articles an attractive finish. Anodised aluminum is highly resistant to corrosion, which is why aluminum strips are used on buses and cars.
Sulfuric acid (H₂SO₄) is called the "king of acids" because it's used in the synthesis of hundreds of industrial products and is one of the most important chemicals in industry. Its major uses include: manufacturing other acids (hydrochloric, nitric), producing fertilizers, refining petroleum, manufacturing detergents and dyes, extracting metals in metallurgy, in car batteries, and in electroplating. The industrial development of a country is often measured by its sulfuric acid production, highlighting its fundamental importance to modern industry.
No. Copper is less reactive than zinc (as per reactivity series), so it cannot displace zinc from its salt solution.
Iron oxide (rust) is porous and flaky, allowing continued exposure to air and moisture. Aluminium oxide forms a non-porous protective layer.
Calcination is heating in limited air (for carbonates/hydrates), while roasting is heating in excess air (for sulphides).
Nitric acid is a strong oxidizing agent that oxidizes hydrogen to water instead of releasing it as a gas.
Aqua regia (3 HCl : 1 HNO₃) dissolves noble metals like gold and platinum, hence called "royal water."
Carats indicate purity. 24-carat gold is 100% pure. Pure gold is too soft for jewelry, so it's alloyed with copper or silver. 22-carat gold contains 22 parts gold and 2 parts other metals.