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

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.

1. 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 at room temperature
• High melting and boiling points, with exceptions like gallium (melts at ~30°C) and caesium (melts at 28.5°C)
• High 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.

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

Mercury melts at −39°C, Gallium at ~30°C, and Caesium at 28.5°C, all liquid at 30°C. Iron, Zinc, Tin, and Lead have much higher melting points.

2. Properties of Non-Metals

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

Physical properties of non-metals:

• Dull appearance, NOT shiny (exception: Iodine is lustrous)
• Poor conductors of heat and electricity (exception: Graphite conducts electricity)
• Brittle, break when hit, not malleable or ductile
• May be solid, liquid, or gas at room temperature

Exceptions to remember:

• Iodine = the only lustrous non-metal
• Graphite = the only non-metal that conducts electricity
• Bromine = the only non-metal that is 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]

3. Atomicity of Non-Metals

The number of atoms in one molecule of a non-metallic element varies.

• Monoatomic: Noble gases, He, Ne, Ar (1 atom per molecule)
• Diatomic: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂ (2 atoms per molecule)
• Tetraatomic: P₄ (4 atoms per molecule)
• Polyatomic: S₈ (8 atoms per molecule)

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

4. Metal Oxides vs Non-Metal Oxides

Metal oxides react with water to form bases or with acids to form salts. They are basic oxides. Example: CaO + H₂O → Ca(OH)₂ (basic solution).

Non-metal oxides react with water to form acids or with bases to form salts. They are acidic oxides. Example: CO₂ + H₂O → H₂CO₃ (acidic solution).

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

Neutral oxide: CO (carbon monoxide) is a neutral oxide. It does not form an acid or base when dissolved in water. [NDA 2025-I]

Amphoteric oxides: Some oxides react with both acids and bases. These are called amphoteric oxides.

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

Amphoteric hydroxides: Al(OH)₃ is amphoteric. It reacts with both HCl (acid) and NaOH (base). [NDA 2014-I]

5. Reactivity Series

The reactivity series (also called the activity series) arranges metals in order of decreasing reactivity. The most reactive metals are at the top. The least reactive (noble metals) are at the bottom.

Reactivity Series (must memorise):

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” (Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Pb (lead), Hydrogen, Copper, Hg (mercury), Ag (silver), Au (gold)).

Key dividing line (Hydrogen):

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

Which metal will NOT react with dilute HCl to produce H₂ = Mercury (Hg), because it is below hydrogen in reactivity series. [NDA 2016-I]

Correct order of electron releasing tendency of metals = Zn > Cu > Ag, more reactive = greater tendency to release electrons. [NDA 2019-II]

Tin (Sn) is ABOVE hydrogen in the reactivity series. It reacts with dilute acids. [NDA 2010-I confirms Tin is above H]

6. Metals Reacting with Water

Metal	Reaction with water	Products
K, Na	Very vigorous, react with cold water	Metal hydroxide + H₂
Ca	Moderate, reacts with cold water	Ca(OH)₂ + H₂
Mg	Slow with cold water, fast with hot water	Mg(OH)₂ + H₂
Al, Zn, Fe	React only with steam	Metal oxide + H₂
Cu, Hg, Ag, Au	Do not react with water	—

Why sodium and potassium are stored under kerosene: K and Na react violently with water, even atmospheric moisture is enough to start a reaction. Kerosene is a non-reactive liquid that keeps these metals away from water and air. [NDA 2008-II]

Least reactive alkali metal with water = Lithium (Li). Reactivity of alkali metals INCREASES down the group. Lithium is the least reactive and Caesium is the most reactive. [NDA 2017-I]

7. Metals in Free State (Native State)

Metals that are very low in the reactivity series are found in nature as free elements (not combined with other elements).

Metals found in free state:

• Gold (Au), always found free [NDA 2006-II]
• Silver (Ag), mostly found free
• Platinum (Pt), found free
• Copper (Cu), sometimes found free

Gold occurs in nature in free state because it is very unreactive. [NDA 2006-II]

8. Important Ores

An ore is a mineral from which a metal can be profitably extracted. An ore is always a mineral but not all minerals are 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 is the ore of Mercury. [NDA 2021-II]

Minerals and their industries: Limestone → Cement | Copper → Electrical goods | Bauxite → Aeroplanes (aluminium) | Manganese → Steel.

Metal extracted by electrolysis of molten compound: Sodium (Na). It is too reactive to be extracted by reduction with carbon. Electrolysis of molten NaCl gives sodium metal at the cathode.

9. Important Metals : Properties and Uses

Metal in haemoglobin = Iron (Fe). Metal in chlorophyll = Magnesium (Mg).

Na-K alloy (nuclear reactor heat transfer): Sodium-potassium alloy (NaK) is used as a coolant to transfer heat in nuclear reactors. It remains liquid over a wide temperature range and is an excellent heat conductor. The metal alloyed with sodium = Potassium. [NDA 2018-I]

Alkali metals (melting point trend): In alkali metals, melting point DECREASES as you go down the group. Li > Na > K > Rb > Cs. Lithium has the HIGHEST melting point. Caesium has the LOWEST melting point. [NDA 2018-I, NDA 2015-II]

Titanium (resists seawater corrosion): Titanium is used for making boats and marine equipment because it does not corrode in seawater.

Gallium and Mercury: Both Gallium and Mercury are liquid at or near room temperature. [NDA 2020-I]

10. Corrosion and Galvanisation

Corrosion is the gradual destruction of a metal by chemical reaction with its environment, mainly oxygen and moisture.

Rusting of iron:

• Requires BOTH oxygen AND water
• Rust = Fe₂O₃·xH₂O (hydrated iron oxide)
• Rust INCREASES the weight of iron

Galvanisation (protecting iron with zinc): A thin layer of zinc is coated on iron/steel. Zinc is MORE reactive than iron (higher in reactivity series). When exposed to moisture and air, zinc corrodes preferentially, protecting the iron beneath. This is called sacrificial corrosion.

Zinc is used for galvanisation because it is more reactive (more electropositive) than iron. [NDA 2013-II, NDA 2017-II, NDA 2021-II]

Sacrificial anode must be MORE reactive than iron. The sacrificial anode corrodes first, protecting the iron.

• Zinc: more reactive than Fe → can be sacrificial anode
• Magnesium: more reactive than Fe → can be sacrificial anode
• Tin: LESS reactive than Fe → CANNOT be sacrificial anode

Food cans are coated with Tin, not Zinc: Tin is used for food cans because it is food-safe and less reactive. However, if the tin coating breaks, iron corrodes faster than tin (tin is less reactive). Zinc is NOT used for food cans because zinc is MORE reactive than tin: if the zinc coating breaks, zinc itself would corrode into the food.

Aluminium resists corrosion: Aluminium is high in the reactivity series but resists corrosion in practice. This is because a thin, transparent layer of Al₂O₃ forms immediately on aluminium’s surface when exposed to air. This layer is tough, adherent, and self-repairing, preventing further oxidation. [NDA 2017-I]

11. Sulphur in Gunpowder

Gunpowder = potassium nitrate (KNO₃) + charcoal (C) + sulphur (S).

The presence of sulphur in gunpowder decreases the ignition temperature, making it easier to ignite. Sulphur does not increase explosiveness directly but lowers the temperature at which the mixture catches fire. [NDA 2013-II]