Metals, Non-Metals and Reactivity Series – NDA Chemistry Notes

Introduction

Look around you — the chair, the door handle, the coins in your pocket, the wire in the wall. Most of these are metals. Metals are the most useful class of materials in human civilisation. But not all elements are metals. Some are non-metals like oxygen and sulphur. Some have properties of both — these are called metalloids.

This chapter covers how metals and non-metals differ, which metals are most and least reactive, what happens when metals react with water and acids, how we protect iron from rusting, and where metals are found in nature.

NDA tests this chapter through reactivity series ordering, displacement reaction feasibility, galvanisation, ore identification, oxide type questions, and specific property questions like which metal is liquid at 30°C and which alkali metal has the lowest melting point.

Properties of Metals

Metals have a set of typical physical and chemical properties. But there are exceptions — and NDA loves testing the exceptions.

Physical properties of metals:

• Shiny (lustrous) appearance
• Good conductors of heat and electricity
• Malleable — can be beaten into thin sheets
• Ductile — can be drawn into wires
• Sonorous — produce a ringing sound when struck
• Solid at room temperature — with one exception: Mercury (Hg) is liquid
• High melting and boiling points — with exceptions (gallium melts at ~30°C, caesium at 28.5°C)
• High density — with exceptions (sodium and potassium float on water — very low density)

Best conductor of heat and electricity = Silver (Ag)
Poorest conductor of heat among common metals = Lead (Pb) [NDA 2010-I]

Softest metal = Sodium (Na) — it can be cut with a knife. [NDA tested via CDS]

Three metals that are liquid at 30°C = Mercury (Hg), Gallium (Ga), Caesium (Cs) [NDA 2007-I]

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Properties of Non-Metals

Non-metals are generally opposite to metals in their properties.

• Dull appearance — NOT shiny (exception: Iodine is lustrous)
• Poor conductors of heat and electricity (exception: Graphite conducts electricity)
• Brittle — break when hit
• May be solid, liquid, or gas at room temperature
• Bromine = only non-metal liquid at room temperature

Metalloids are elements that have some properties of metals and some of non-metals. Examples: Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb). [NDA 2013-II]

Metals vs Non-Metals — Comparison Table

Property	Metals	Non-Metals
Lustre	Shiny	Dull (except Iodine)
Conductivity	Good (heat + electricity)	Poor (except Graphite)
Malleability	Yes	No — brittle
Ductility	Yes	No
Physical state	Mostly solid	Solid, liquid, or gas
Oxide type	Basic	Acidic
Ion formed	Cation (loses electrons)	Anion (gains electrons)
Example	Fe, Cu, Al, Na, K	O₂, N₂, S, P, Cl₂, C

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Important Non-Metals Table

Non-Metal	Key Property	Common Use
Oxygen (O₂)	Supports combustion	Respiration, steel making, oxy-acetylene welding
Nitrogen (N₂)	Inert, 78% of atmosphere	Fertilisers, food packaging, liquid N₂ coolant
Sulphur (S₈)	Yellow solid, polyatomic	H₂SO₄ manufacturing, vulcanisation, gunpowder
Phosphorus (P₄/P)	White P ignites in air	Fertilisers, safety matches (red P)
Chlorine (Cl₂)	Yellow-green toxic gas	Water disinfection, bleaching, PVC
Carbon (C)	Multiple allotropes	Diamond (cutting), graphite (electrodes, pencils)

Sulphur is polyatomic — exists as S₈ molecules. [NDA 2024-II]

Sulphur in gunpowder decreases the ignition temperature. [NDA 2013-II]

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Important Metals Table

Important Metals Table

Metal	Key Property	Common Use
Iron (Fe)	Strong, rusts in air	Construction, steel, machinery
Copper (Cu)	Excellent electrical conductor	Electrical wires, plumbing, coins
Aluminium (Al)	Lightweight, resists corrosion	Aircraft, utensils, packaging
Zinc (Zn)	Amphoteric oxide, galvanisation	Protecting iron, dry cells, alloys
Silver (Ag)	Best conductor of electricity	Jewellery, photography, electrical contacts
Gold (Au)	Most malleable, noble	Jewellery, electronics
Mercury (Hg)	Only liquid metal at RT	Thermometers, barometers
Lead (Pb)	Dense, poor conductor	Batteries, radiation shielding
Sodium (Na)	Very reactive, low density, soft	Chemical manufacture, Na vapour lamps
Platinum (Pt)	Noble, excellent catalyst	Catalytic converters, jewellery

Metal in haemoglobin = Iron (Fe) [NDA 2011-II, NDA tested via CDS]
Metal in chlorophyll = Magnesium (Mg) [NDA 2011-II, NDA tested via CDS]

Na-K alloy is used as coolant to transfer heat in nuclear reactors. The metal alloyed with sodium = Potassium. [NDA 2018-I]

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Atomicity of Non-Metals

• Monoatomic: Noble gases — He, Ne, Ar
• Diatomic: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂
• Tetraatomic: P₄
• Polyatomic: S₈

Sulphur is polyatomic — S₈. [NDA 2024-II]

Metal Oxides vs Non-Metal Oxides

Metal oxides are basic — they react with acids to form salt and water.
Non-metal oxides are acidic — they react with water to form acids or with bases to form salts.

Oxygen on reaction with non-metals forms oxides which are acidic. [NDA 2013-II]

Neutral oxide: CO (carbon monoxide) — does not react with water, acid, or base. [NDA 2025-I]

Amphoteric oxides react with BOTH acids AND bases:

• Al₂O₃ (aluminium oxide)
• ZnO (zinc oxide)

Amphoteric hydroxide: Al(OH)₃ — reacts with both HCl and NaOH. [NDA 2014-I]

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Reactivity Series

The reactivity series arranges metals in decreasing order of reactivity.

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

Memory trick: “Please Stop Calling Me A Zoologist, I Prefer Having Chemistry Helping Around”

Key rule — Hydrogen as dividing line:

• Metals ABOVE hydrogen → react with dilute acids to release H₂
• Metals BELOW hydrogen (Cu, Hg, Ag, Au) → do NOT react with dilute acids

Mercury (Hg) does NOT react with dilute HCl to give H₂ — it is below hydrogen. [NDA 2016-I]

Correct order of electron releasing tendency = Zn > Cu > Ag [NDA 2019-II]

Metals Reacting with Water

Metal	Reaction	Products
K, Na	Very vigorous with cold water	Metal hydroxide + H₂
Ca	Moderate with cold water	Ca(OH)₂ + H₂
Mg	Slow with cold, fast with hot water	Mg(OH)₂ + H₂
Al, Zn, Fe	React only with steam	Metal oxide + H₂
Cu, Hg, Ag, Au	No reaction with water	—

Sodium and potassium are stored under kerosene because they react violently with water and atmospheric moisture. [NDA 2008-II]

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Displacement Reactions — Feasibility Table

A more reactive metal displaces a less reactive metal from its salt solution. A less reactive metal CANNOT displace a more reactive one.

Reaction	Feasible?	Reason
Zn + CuSO₄ → ZnSO₄ + Cu	✓ Yes	Zn more reactive than Cu
Fe + CuSO₄ → FeSO₄ + Cu	✓ Yes	Fe more reactive than Cu
Mg + CuSO₄ → MgSO₄ + Cu	✓ Yes	Mg more reactive than Cu
Pb + CuCl₂ → PbCl₂ + Cu	✓ Yes	Pb more reactive than Cu
Cu + FeSO₄ → No reaction	✗ No	Cu less reactive than Fe
Ag + ZnSO₄ → No reaction	✗ No	Ag less reactive than Zn
Cu + PbCl₂ → No reaction	✗ No	Cu less reactive than Pb

When iron nail is placed in CuSO₄ solution — iron displaces copper. The solution turns from blue to green (CuSO₄ is blue, FeSO₄ is green). Iron is the reducing agent. [NDA 2019-I, NDA 2023-I]

Metals in Free State

Metals low in the reactivity series are found in nature in free (uncombined) state.

Found free in nature: Gold (Au), Silver (Ag), Platinum (Pt), Copper (Cu — sometimes)

Gold occurs in nature in free state. [NDA 2006-II]

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Important Ores

Metal	Ore name	Formula
Iron (Fe)	Haematite	Fe₂O₃
Iron (Fe)	Magnetite	Fe₃O₄
Aluminium (Al)	Bauxite	Al₂O₃·2H₂O
Mercury (Hg)	Cinnabar	HgS
Copper (Cu)	Copper pyrites	CuFeS₂
Zinc (Zn)	Zinc blende	ZnS
Lead (Pb)	Galena	PbS
Silver (Ag)	Argentite	Ag₂S

Cinnabar = ore of Mercury. [NDA 2021-II]

Extraction of Metals — Conceptual Level

The method of extraction depends on where the metal sits in the reactivity series.

Reactivity	Method	Example
Very reactive (K, Na, Ca, Mg, Al)	Electrolysis of molten compound	Al from bauxite, Na from molten NaCl
Moderately reactive (Zn, Fe, Pb, Cu)	Reduction with carbon or CO	Fe from haematite in blast furnace
Least reactive (Hg, Ag, Au)	Heating alone or physical separation	Hg from cinnabar by roasting

Sodium is extracted by electrolysis of molten NaCl. Very reactive metals cannot be reduced by carbon — too much energy needed. [NDA tested via CDS]

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Ferrous vs Non-Ferrous Metals

Type	Definition	Examples
Ferrous	Iron-based	Iron, steel, cast iron, stainless steel
Non-ferrous	No significant iron	Copper, aluminium, zinc, gold, silver

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Corrosion and Rusting

Corrosion = gradual destruction of metal by chemical reaction with environment.

Rusting of iron:

• Requires BOTH oxygen AND water — remove either and rusting stops
• Rust = Fe₂O₃·xH₂O (hydrated iron oxide)
• Rust is a COMPOUND — not a mixture
• Rusting INCREASES weight of iron (oxygen and water are added)

Why aluminium resists corrosion despite being reactive:
A thin, transparent Al₂O₃ layer forms immediately on aluminium’s surface when exposed to air. This layer is tough, adherent, and self-repairing — it prevents further oxidation. This is why aluminium is used in aircraft and utensils despite being high in the reactivity series.

Prevention of Corrosion

Method	How it works	Example
Painting	Physical barrier — excludes O₂ and moisture	Iron bridges, gates, railings
Oiling / Greasing	Barrier + water displacement	Machine parts, tools
Galvanisation	Zinc coating — zinc corrodes sacrificially	Galvanised iron sheets, roofing
Electroplating	Thin corrosion-resistant metal deposited	Chrome on car bumpers, tin on food cans
Alloying	Create corrosion-resistant alloy	Stainless steel (Fe + Cr + Ni)
Cathodic protection	More reactive metal attached — corrodes first	Ships, underground pipelines (Mg or Zn anode)
Anodising	Thickens natural Al₂O₃ layer electrochemically	Aluminium frames, cookware

Galvanisation — zinc protects iron:
Zinc is MORE reactive than iron. Zinc corrodes first — protecting iron as long as any zinc remains. This is called sacrificial corrosion. [NDA 2013-II, NDA 2017-II, NDA 2021-II]

Sacrificial anode must be MORE reactive than iron:

• Zinc ✓ | Magnesium ✓ | Aluminium ✓ — all more reactive than Fe
• Tin ✗ — LESS reactive than Fe — CANNOT be sacrificial anode [NDA tested via CDS]

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