Introduction and Physical Properties

Metals and Non-Metals — Introduction

All around us, the elements fall into two main classes — metals and non-metals.

Can You Recognise These?

• Iron, copper, gold, silver — metals
• Coal (carbon), sulphur, phosphorus — non-metals
• Hydrogen, oxygen, chlorine — gaseous non-metals

Position in the Periodic Table

• Left side: most elements are metals.
• Right side: most elements are non-metals.
• Centre band: a few metalloids — like $Si, Ge, As, Sb, Te$.

Distribution of Elements

• Total known elements ~ 118
• Metals ~ 78%
• Non-metals ~ 22%

Why Are Metals Important?

1. Construction: iron, steel, aluminium.
2. Daily life: utensils, tools, jewellery.
3. Transport: cars, trains, aircraft.
4. Electricity: copper/aluminium wires.
5. Industry: machines, structures.

Why Are Non-Metals Important?

1. For life: oxygen (breath), carbon (organic compounds).
2. In food: iodine (in salt), phosphorus (bones).
3. Chemical industry: sulphur, chlorine.
4. Diamond: the world's hardest substance.
5. Fertilisers: nitrogen.

[Board Tip] Identify metals vs. non-metals from their physical properties.

Physical Properties of Metals

1. Metallic Lustre

Metal surfaces are shiny — when freshly cut.

Examples:

• Gold (Au) — yellow lustre
• Silver (Ag) — white lustre
• Copper (Cu) — reddish-brown

2. Hardness

Most metals are hard.

Exceptions: sodium (Na), potassium (K) — can be cut with a knife (soft).

3. Malleability

Metals can be hammered into thin sheets.

Examples:

• Gold leaf — silver foil.
• Aluminium foil — for food packaging.
• 1 g of gold can be hammered into ~ 100 sq cm of foil.

4. Ductility

Metals can be drawn into thin wires.

Examples:

• Copper — electrical wires.
• Aluminium — high-tension wires.
• Gold is the most ductile — 1 g can be drawn into a 2 km long wire.

5. Conductivity

Metals are good conductors of heat and electricity.

Best conductors (in decreasing order):

• Electricity: $Ag > Cu > Au > Al$
• Heat: $Ag > Cu > Au > Al$

Exceptions: lead (Pb) and mercury (Hg) — poor conductors.

6. Sonorousness

Metals produce a ringing sound when struck.

Examples:

• Temple bells (bronze, brass)
• The school bell

7. High Melting/Boiling Points

• Most metals are solids.
• High melting points — tungsten (W) melts at ~ 3422°C.
• Exception: mercury (Hg) — liquid (mp −39°C).

8. Density

• Most metals are dense.
• Exceptions: sodium and potassium — light (less dense than water).

[Board Important] 6 physical properties of metals and their exceptions.

Physical Properties of Non-Metals

The properties of non-metals are mostly the opposite of metals.

1. Lack of Lustre

Non-metals are usually dull (not shiny).

Exception: iodine (I₂) — appears shiny, almost metallic.

2. Hardness

Most non-metals are soft.

Exception: diamond (carbon) — the hardest natural substance.

3. Brittleness

Non-metals shatter when struck — not malleable.

Example: sulphur — shatters under a hammer.

4. Poor Conductors

Non-metals are poor conductors of heat and electricity.

Exception:

• Graphite (an allotrope of carbon) — a good conductor of electricity.
• (A very important exception at the Class 10 level.)

5. Not Sonorous

Non-metals do not ring when struck (or shatter).

6. Variety of States

• Solid: carbon, sulphur, phosphorus, iodine
• Liquid: bromine (Br₂) — the only liquid non-metal at ordinary temperatures
• Gas: oxygen, nitrogen, chlorine, hydrogen

7. Low Melting/Boiling Points

Far lower than metals.

Exception: diamond — extremely high melting point (~ 3550°C, higher than many metals).

8. Low Density

Most non-metals are light.

Exceptions for Non-Metals — A Summary

Property	Typical	Exception
Lustre	Dull	Iodine — shiny
Hardness	Soft	Diamond — hardest
Conductivity	Poor	Graphite — good conductor
Melting point	Low	Diamond — very high

[Board Important] Memorise the exceptions — they are asked frequently.

Metals vs. Non-Metals — Comparison of Physical Properties

This is the most important summary table for the Class 10 exam:

Property	Metals	Non-Metals
Lustre	Metallic lustre	Dull (exc. iodine)
State	Mostly solid	Solid/liquid/gas
Hardness	Hard (exc. Na, K)	Soft (exc. diamond)
Malleability	Yes	No (brittle)
Ductility	Yes	No
Electrical conductivity	Good	Poor (exc. graphite)
Heat conductivity	Good	Poor
Sonorousness	Yes	No
Melting point	High (exc. Na, K, Hg)	Low (exc. diamond)
Density	High (exc. Na, K)	Low

The Key Exceptions That Come Up in Exams

Exceptions for metals:

• Mercury (Hg): liquid at room temperature (mp −39°C).
• Sodium (Na), potassium (K): soft — can be cut with a knife.
• Lithium (Li): the lightest metal — floats on water.
• Gallium (Ga), caesium (Cs): melt with the warmth of the hand.

Exceptions for non-metals:

• Diamond (carbon): the hardest natural substance.
• Graphite (carbon): a good conductor of electricity.
• Iodine (I₂): appears shiny.
• Bromine (Br₂): liquid at room temperature.

Why These Properties?

Metals have 'free electrons':

• These electrons move freely through the metal.
• That's the source of electrical and thermal conduction.
• And of lustre too (electrons reflect light).

Non-metals have no free electrons:

• Covalent bonding — electrons are shared, not free.
• Hence poor conduction.
• (Graphite has free electrons — that's why it's an exception.)

[Board Important] This table is often a 5-mark question.

Metalloids and Some Curious Facts

What Are Metalloids?

Some elements show properties of both metals and non-metals — these are called metalloids.

Main metalloids: B, Si, Ge, As, Sb, Te, Po

Properties of Metalloids

• Slightly shiny
• Moderate hardness
• Moderate electrical conductivity
• Semiconductors — useful in electronics

Uses

Silicon (Si):

• Computer chips
• Solar panels
• The basis of 'Silicon Valley'

Germanium (Ge):

• Transistors
• Semiconductors

Some Curious Facts

1. Most-used metal: iron (Fe) — over 90% of all metal production.

2. Most expensive metal: rhodium (Rh) — costlier than gold.

3. Lightest metal: lithium (Li).

4. Heaviest common metal: osmium (Os) — twice as heavy as gold.

5. The only liquid metal (at ordinary temperatures): mercury (Hg).

6. The only liquid non-metal: bromine (Br₂).

7. Hardest natural substance: diamond (carbon).

8. Best electrical conductor: silver (Ag).

9. Most ductile metal: gold (Au).

10. Most malleable: gold and silver.

A Curious Experiment

On dropping sodium (Na) into water:

• Vigorous reaction.
• $H_2$ gas is released.
• Highly exothermic — fire may even start.
• That's why Na is stored under kerosene.

(Detail in Section 2.)

🧠 Memory Capsule

A one-glance recap just before the board exam.

1. Metal vs. Non-Metal — Main Properties

Property	Metal	Non-metal
Lustre	Metallic	Dull
Malleability	Yes	No
Ductility	Yes	No
Conductivity	Good	Poor
Sonorousness	Yes	No
Melting point	High	Low

2. Important Exceptions

Exceptions for metals:

• Hg — liquid
• Na, K — soft
• Li — light (floats on water)

Exceptions for non-metals:

• Diamond — hard, high melting point
• Graphite — good conductor
• Iodine — shiny
• Br₂ — liquid

3. Top Conducting Metals

• Electricity: $Ag > Cu > Au > Al$
• Heat: $Ag > Cu > Au > Al$

4. A Few Numerical Facts

• Total elements: ~118
• Metals: ~78%
• Non-metals: ~22%

5. Metalloids

• B, Si, Ge, As, Sb, Te, Po
• Semiconductors — used in electronics.

6. Interesting Facts

• Most ductile: gold
• Best conductor: silver
• Hardest: diamond
• Only liquid metal: mercury
• Only liquid non-metal: bromine

7. Board's 'Golden' Questions

1. Compare 5 physical properties of metals and non-metals.
2. Why is mercury the only liquid metal?
3. How does graphite conduct electricity? Explain.
4. What are metalloids? Examples.
5. Why are Na/K stored in kerosene?

The Bottom Line: Metal = lustre, conductor, malleable; non-metal = dull, poor conductor, brittle. Memorise the exceptions.

Solved Examples

Example 1: NCERT — Five Physical Properties of Metals

Discuss five physical properties of metals. Give an example of each.

Solution:

1. Metallic lustre: Gold, silver, copper — all are shiny. The freshly cut surface is especially bright.

2. Malleability: Hammered into thin sheets. Examples — gold leaf, aluminium foil.

3. Ductility: Drawn into thin wires. Example — copper wires. 1 g of gold makes a 2 km wire.

4. Electrical conductivity: Conduct electricity well. Example — Ag > Cu > Au > Al.

5. Sonorousness: Ring when struck. Examples — temple bells (bronze, brass).

Other properties:

• Heat conductivity
• High melting/boiling points
• Hardness
• High density

[NCERT textbook question]

Example 2: NCERT — Mercury — The Only Liquid Metal

Mercury (Hg) is the only liquid metal at room temperature. Why is this so?

Solution:

At ordinary temperatures:

• Most metals are solid.
• Sodium/potassium — soft but solid.
• Gallium (Ga) — melts at hand-warmth (~30°C).

Mercury's melting point: −39°C (very low!)

So at ordinary room temperature (~25°C) — mercury is a liquid.

Reason (simplified at Class 10 level):

• The metallic bonding in mercury is weak.
• Its electron arrangement makes electron-sharing weak.
• (Explained in Class 11-12 by the 'inert pair effect'.)

Uses of mercury:

• Thermometers (temperature measurement)
• Barometers
• Fluorescent lamps

Caution: Mercury is toxic — be careful with broken thermometers.

[Board 2-3 marks]

Example 3: NCERT — The Graphite Exception

Graphite is a non-metal yet a good conductor of electricity. Why?

Solution:

General rule: Non-metals are poor conductors of electricity. Graphite is an exception.

Explanation (the structure of graphite):

1. Arrangement of carbon atoms:

• Carbon atoms in graphite are arranged in hexagonal sheets.
• Each carbon is bonded to three other carbons (three covalent bonds).
• Of carbon's 4 outer electrons, 3 are in bonds; 1 remains free.

1. The role of free electrons:

• These free electrons can move between the layers.
• Electrical conduction comes from these free electrons.
• That is, graphite has 'metal-like' electrical conduction.

Other interesting properties:

• Graphite is soft — used in pencil leads.
• Slippery — used as a dry lubricant.
• High melting point — used in electric furnaces.

Diamond vs. graphite — both are carbon allotropes:

Property	Diamond	Graphite
Structure	Three-dimensional (3D)	Layered (2D)
Bonds	4 (no free electron)	3 (1 free electron)
Conductor	Poor	Good
Hardness	Very hard	Soft

[Board 3-mark question]

Example 4: NCERT — Why Are Na/K Stored in Kerosene?

Why are reactive metals like sodium and potassium stored in kerosene?

Solution:

The nature of Na and K:

• Highly reactive metals.
• React quickly when exposed to air.
• React explosively with moisture.

What happens on exposure to air?

(1) With oxygen: $$4Na + O_2 \rightarrow 2Na_2O$$ (surface tarnishes quickly)

(2) With water/moisture: $$2Na + 2H_2O \rightarrow 2NaOH + H_2\uparrow + \text{Heat}$$ (the released $H_2$ can ignite — highly exothermic)

Why kerosene?

Kerosene's properties:

1. Hydrocarbon — an organic oil.
2. Water-repellent — keeps moisture away.
3. Air-tight — keeps Na/K away from $O_2$.
4. Chemically inert — does not react with Na/K.

Thus kerosene keeps Na/K safe.

Precautions:

• Never touch with bare hands.
• Don't let water droplets near (Na/K react violently).
• Use tongs in the lab.

Other metals stored carefully:

• Lithium (Li): also under kerosene.
• Mercury (Hg): sealed glass containers (to prevent vapour).
• Caesium (Cs): very fast reaction — kept in oil or vacuum.

[NCERT textbook — repeatedly asked]

Example 5: A Numerical on Gold's Ductility

How long a wire can be drawn from 1 g of gold? Why is this possible?

Solution:

Fact: From 1 g of gold, a wire about 2 km long can be drawn — extremely fine!

How is this possible?

The reason for ductility:

1. Gold atoms can 'slide' over one another.
2. Metallic bonds are very strong — they keep atoms connected.
3. But they are flexible — they allow shape changes.
4. So the metal stretches into a long wire.

Why is gold the most ductile?

• Gold's metallic bonding is very strong.
• The arrangement of atoms is uniform.
• Almost no defects — it doesn't break.

Other ductile metals (in decreasing order): Au > Ag > Cu > Al > Fe

Uses of ductility:

• Electrical wires
• In electronics
• In jewellery

Malleability vs. ductility:

Property	Meaning	Example
Malleability	Hammered into sheets	Gold leaf
Ductility	Drawn into wires	Copper wires

Most metals show both — but to different degrees.

Example 6: NCERT — Why Is Silver the Best Conductor?

Which is the best conductor of electricity? Why isn't silver used in wires?

Solution:

Order of electrical conductivity:

$$Ag > Cu > Au > Al > Fe$$

Best conductor: silver (Ag) — has the most free electrons.

But why isn't silver used in wires?

Reasons:

1. Cost: silver is very expensive — copper is cheap.
2. Availability: silver is rare; copper is abundant.
3. Durability: silver tarnishes quickly (Ag₂S) — corrosion.
4. Copper is sufficient: Cu is only slightly less conductive than Ag — practically negligible.

Real uses:

• Household wiring: copper (Cu)
• High-tension wires: aluminium (light, cheap)
• Special electronics: gold (Au) — corrosion-resistant
• Lab instruments: silver (small amounts)

Lesson: 'Best' isn't always 'most used' — practicality and cost matter too.

[Board 3-mark question]

Example 7: The Diamond Exception

Diamond is a non-metal, yet it is extremely hard and has a very high melting point. Why?

Solution:

Diamond = an allotrope of carbon (C) — the element is just carbon.

Special properties:

• The hardest natural substance
• Melting point ~ 3550°C
• Poor conductor of electricity
• Highly transparent and lustrous

Why these properties? — because of structure.

Diamond's structure:

1. Three-dimensional (3D) network:

• Each carbon is covalently bonded to 4 other carbons.
• Tetrahedral geometry.

1. All 4 electrons are in bonds: no free electrons.
2. The whole crystal is one 'giant molecule': giant covalent structure.

What does this give us?

• Hardness: all bonds are strong — hard to break anything.
• High melting point: breaking all bonds takes a lot of energy.
• Poor electrical conduction: no free electrons.
• Transparency: light cannot excite any free electrons.

Uses of diamond:

1. Jewellery — the most expensive gemstone.
2. Industrial cutting tools — due to hardness.
3. Lathe machines.
4. Blades — for cutting glass.

Diamond vs. graphite (both are carbon):

Property	Diamond	Graphite
Structure	3D	2D layered
Bonds	4	3 (1 free)
Conductor	No	Yes
Hardness	Extremely	Soft
Use	Jewellery	Pencil, lubricant

[Board 5-mark question]

Example 8: NCERT — The Iodine Exception

Iodine is a non-metal yet its surface has a metallic lustre. Why?

Solution:

General rule: non-metals are not lustrous.

The iodine exception:

• Iodine crystals are dark purple-black.
• The surface displays a metallic lustre.

Reason (simplified):

• Atoms in $I_2$ molecules are tightly packed.
• A regular arrangement in the crystal lattice.
• Light is reflected from the surface — giving lustre.
• (Full explanation in Classes 11-12.)

Other properties (iodine):

• Solid at room temperature.
• Sublimes — goes directly from solid to gas on heating.
• Gaseous iodine is violet.
• Used as an antiseptic (tincture of iodine).
• Important for health (iodised salt — prevents goitre).

Other similar exceptions:

• Graphite — conducts electricity.
• Diamond — hardest substance.
• Selenium (Se): some metallic properties.

Lesson: Not every property of non-metals applies universally — exceptions appear in exams.

[Board 2-mark question]

Example 9: A Comparative Question

Make a table and fill in the physical properties of these elements — Cu, S, Hg, I₂, graphite: (a) State (b) Lustre (c) Conductivity (d) Hardness

Solution:

Element	State	Lustre	Electrical Conductivity	Hardness
Cu (copper)	Solid	Metallic	Good	Hard
S (sulphur)	Solid	Dull	Poor	Soft
Hg (mercury)	Liquid (exc!)	Metallic	Good	Liquid — N/A
I₂ (iodine)	Solid	Metallic (exc!)	Poor	Soft
Graphite	Solid	Slight	Good (exc!)	Soft

Main exceptions here:

1. Mercury — a liquid metal.
2. Iodine — a shiny non-metal.
3. Graphite — a non-metal that conducts electricity.

Lesson: Both rules and exceptions matter.

[Board 5-mark question]

Example 10: An Interesting Comparison — Gold vs. Iron

Gold (Au) and iron (Fe) — both are metals. Compare their properties.

Solution:

Property	Gold (Au)	Iron (Fe)
Colour	Golden-yellow	Brown-grey
Lustre	Highly lustrous	Moderate
Melting point	1064°C	1538°C
Hardness	Soft	Hard
Density	19.3 g/cm³ (very heavy)	7.87 g/cm³
Corrosion	None (noble metal)	Quickly (rust)
Reactivity	Very low	Moderate
Use	Jewellery, electronics	Construction, machines
Cost	Very expensive	Cheap

Key interesting facts:

1. Gold is the most ductile: 1 g → 2 km wire.

2. Gold is corrosion-resistant: stays the same for thousands of years.

3. Iron is the most-used: ~ 90% of all metal production.

4. Their alloys:

• Gold: 24-carat (pure) to 22/18/14-carat (alloyed).
• Iron: steel, stainless steel, cast iron.

Lesson: Even within a single class (metals), properties can differ greatly.

Example 11: NCERT — The Difference Between Aluminium and Sodium

Aluminium and sodium — both are metals, but aluminium is hard while sodium is soft. Why?

Solution:

Main differences:

Property	Al	Na
Reactivity	Moderate	Very high
Hardness	Hard	Very soft
Bonding	Strong metallic	Weak metallic
Use	Construction	Stored in kerosene

Why is Na soft?

1. Sodium's metallic bonding is weak — low binding force between atoms.
2. Only 1 outer electron per atom — the 'sea' of free electrons is sparse.
3. Larger atoms — bond distance is bigger.

Why is Al hard?

1. Aluminium has 3 outer electrons — many more free electrons.
2. Metallic bonding is three times stronger.
3. Smaller atoms — packed tightly.

Daily-life examples:

• Sodium — can be cut with a knife (like butter).
• Aluminium — cannot be cut with a knife.

Uses:

• Na — chemical industry, street lamps (sodium vapour lamps).
• Al — aircraft, utensils, food packaging.

Lesson: The strength of metallic bonding (number of outer electrons) determines hardness.

Example 12: A Challenging Question — Metalloids

What are metalloids? Give four examples and their uses.

Solution:

Definition: Elements that show properties of both metals and non-metals are called metalloids.

In the periodic table: along the 'staircase' line between metals and non-metals.

Main metalloids: B, Si, Ge, As, Sb, Te, Po

Four examples and uses:

1. Boron (B):

• Properties: hard, slightly lustrous, poor conductor.
• Uses:
• Borosilicate glass (Pyrex) — heat-resistant.
• Soap, borax.
• Control rods in nuclear reactors.

2. Silicon (Si):

• Properties: lustrous, semiconductor.
• Uses:
• Computer chips (the basis of the entire digital age).
• Solar panels.
• Glass manufacture.
• The name 'Silicon Valley' comes from this.

3. Germanium (Ge):

• Properties: semiconductor.
• Uses:
• Early transistors.
• Fibre optics.

4. Arsenic (As):

• Properties: toxic, semiconductor.
• Uses:
• Electronics (GaAs).
• Pesticides (older).

Special role of metalloids:

• The basis of the semiconductor industry.
• Computers, mobiles, solar panels — all depend on them.
• A pillar of modern technology.

[Board 3-5 marks]

Example 13: Numerical — Density

A metal has a density of 8.9 g/cm³. What is the mass of 100 cm³ of this metal?

Solution:

Formula: density = $\frac{\text{mass}}{\text{volume}}$

So: $\text{mass} = \text{density} \times \text{volume}$

Given:

• density = 8.9 g/cm³
• volume = 100 cm³

Calculation:

$$\text{mass} = 8.9 \times 100 = 890 \text{ g}$$

Answer: 890 g.

Special note: Density 8.9 g/cm³ — this is copper (Cu).

Densities of other metals:

Metal	Density (g/cm³)
Li	0.53 (floats on water)
Na	0.97
Mg	1.74
Al	2.70
Fe	7.87
Cu	8.96
Ag	10.49
Pb	11.34
Au	19.30 (very heavy)
Os	22.59 (the heaviest)

Example 14: A True/False Question

State whether the following are true or false: (a) All metals are hard. (b) Graphite is a conductor of electricity. (c) Mercury is a liquid non-metal. (d) Non-metals are not malleable. (e) Diamond is the hardest natural substance.

Solution:

(a) False — Na, K are soft metals — they can be cut with a knife.

(b) True ✓ — Graphite has free electrons — a good conductor of electricity.

(c) False — Mercury is a liquid metal (not non-metal). Bromine is the only liquid non-metal.

(d) True ✓ — Non-metals are brittle — they shatter when struck.

(e) True ✓ — Diamond (an allotrope of carbon) is the hardest natural substance.

Final summary table:

Statement	True/False
(a)	False
(b)	True
(c)	False
(d)	True
(e)	True

Example 15: NCERT — Black Coating on Silver

Why do silver objects develop a black coating over time? What compound is it?

Solution:

Cause: A trace amount of hydrogen sulphide ($H_2S$) is present in the atmosphere. It slowly reacts with silver.

Reaction:

$$4Ag(s) + 2H_2S(g) + O_2(g) \rightarrow 2Ag_2S(s) + 2H_2O(l)$$

Compound formed: silver sulphide ($Ag_2S$) — black coating.

What kind of process is this?

• Corrosion — slow chemical destruction of a metal.
• It's also an oxidation reaction.

In daily life:

• Silver kept near milk, eggs, or onions blackens faster — these foods contain natural sulphur compounds.

Cleaning methods:

1. Rubbing with toothpaste:

• Toothpaste has a mild abrasive — removes the black layer.

2. Aluminium foil + baking soda:

• Dissolve baking soda (NaHCO₃) in hot water.
• Place silver on aluminium foil.
• A surprising chemical reaction occurs — Al displaces Ag from $Ag_2S$:

$$3Ag_2S + 2Al \rightarrow 6Ag + Al_2S_3$$

(Section 5 — connected to corrosion.)

[Board 3-mark question]

Example 16: A Closing Multi-Topic Question

(a) Five main differences between metals and non-metals. (b) Three famous exceptions for metals. (c) Three famous exceptions for non-metals. (d) The best electrical conductor metal.

Solution:

(a) Five main differences:

Property	Metal	Non-metal
Lustre	Metallic	Dull
Malleability	Yes	No
Ductility	Yes	No
Electrical conductivity	Good	Poor
Melting point	High	Low

(b) Three exceptions for metals:

1. Mercury (Hg) — a liquid metal at room temperature.
2. Sodium (Na), potassium (K) — soft metals (can be cut with a knife).
3. Lithium (Li) — the lightest metal (floats on water).

(c) Three exceptions for non-metals:

1. Diamond — the hardest substance; high melting point.
2. Graphite — a good conductor of electricity.
3. Iodine — a lustrous solid.

(d) The best electrical conductor: silver (Ag) — most free electrons.

But for wires, copper is used — cheaper and almost as good.

[Board 5-mark question]