Chapter 27: Metals and Non-metals

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1. Physical Properties & Key Exceptions

Elements are electrochemically classified based on their electron transfer tendencies:

Metals (Electropositive): Readily lose valence electrons to form cations ($\text{M} \to \text{M}^{n+} + ne^-$).
Non-Metals (Electronegative): Readily gain or share electrons to complete an octet ($\text{X} + ne^- \to \text{X}^{n-}$).

Property	Metals	Non-Metals	Crucial Exceptions
Malleability & Ductility	Malleable (beaten into sheets) and ductile (drawn into wires). Gold ($\text{Au}$) is most malleable & ductile.	Neither malleable nor ductile; brittle (e.g., sulphur, coal).	Zinc is brittle at room temperature.
Metallic Lustre	Lustrous shiny surface.	Dull appearance.	Iodine ($\text{I}_2$) is a non-metal with metallic lustre.
Hardness & State	Hard solids with high tensile strength.	Exist as solids, liquid ($\text{Br}_2$), and gases.	• Mercury ($\text{Hg}$) is liquid at room temperature. • Alkali metals ($\text{Na, K, Li}$) are soft; can be cut with a knife. • Diamond (carbon allotrope) is the hardest natural substance.
Melting & Boiling Points	Generally very high.	Generally low.	Gallium ($\text{Ga}$) and Caesium ($\text{Cs}$) melt in the palm of your hand ($<30^\circ\text{C}$). Diamond has an extremely high MP ($>3500^\circ\text{C}$).
Conductivity	Good conductors of heat and electricity.	Poor conductors (insulators).	• Best conductors: Silver ($\text{Ag}$) and Copper ($\text{Cu}$). • Poor conductors: Lead ($\text{Pb}$) and Mercury ($\text{Hg}$). • Graphite (carbon allotrope) is an excellent electrical conductor.
Sonorous & Density	Sonorous (produce ringing sound); high density.	Non-sonorous; low density.	$\text{Na}$ and $\text{K}$ have densities lower than water (float on water).

Figure 27.1: Demonstration of Thermal Conductivity in Metals

2. Chemical Properties & Key Reactions

A. Reaction with Oxygen (Air):

Metals form basic oxides. Sodium and potassium react vigorously and are stored under kerosene oil:

$$4\text{Na} + \text{O}_2 \;\longrightarrow\; 2\text{Na}_2\text{O}$$ $$\text{Na}_2\text{O} + \text{H}_2\text{O} \;\longrightarrow\; 2\text{NaOH} \quad (\text{Alkaline base, turns red litmus blue})$$ $$2\text{Mg} + \text{O}_2 \;\longrightarrow\; 2\text{MgO}$$

B. Amphoteric Oxides (Dual Acidic & Basic Behavior):

Certain metallic oxides react with both acids and bases to produce salt and water:

Aluminium Oxide ($\text{Al}_2\text{O}_3$): $$\text{Al}_2\text{O}_3 + 6\text{HCl} \;\longrightarrow\; 2\text{AlCl}_3 + 3\text{H}_2\text{O} \quad (\text{Basic action})$$ $$\text{Al}_2\text{O}_3 + 2\text{NaOH} \;\longrightarrow\; 2\text{NaAlO}_2 + \text{H}_2\text{O} \quad (\text{Acidic action: Sodium Aluminate})$$
Zinc Oxide ($\text{ZnO}$): $$\text{ZnO} + 2\text{NaOH} \;\longrightarrow\; \text{Na}_2\text{ZnO}_2 + \text{H}_2\text{O} \quad (\text{Sodium Zincate})$$
Tin ($\text{Sn}$) with Excess Base (NIOS Specific Equation): $$\text{Sn} + 2\text{NaOH} + \text{H}_2\text{O} \;\longrightarrow\; \underset{\text{Sodium Stannate}}{\text{Na}_2\text{SnO}_3} + 2\text{H}_2\uparrow$$

C. Reaction with Water & Steam:

Cold Water: $\text{Na}$ and $\text{K}$ react violently; $\text{Ca}$ floats: $$2\text{Na} + 2\text{H}_2\text{O} \;\longrightarrow\; 2\text{NaOH} + \text{H}_2\uparrow + \text{Heat}$$
Hot Water: $\text{Mg} + 2\text{H}_2\text{O(l)} \;\longrightarrow\; \text{Mg(OH)}_2 + \text{H}_2\uparrow$
Steam Only ($\text{Al, Fe, Zn}$): Form metal oxides (not hydroxides) and $\text{H}_2$: $$3\text{Fe} + 4\text{H}_2\text{O(g)} \;\longrightarrow\; \text{Fe}_3\text{O}_4 + 4\text{H}_2\uparrow$$

Figure 27.2: Action of Steam on a Metal Sample

D. Reaction with Acids & The Reactivity Series:

$$\text{Metal} + \text{Dilute Acid} \;\longrightarrow\; \text{Salt} + \text{H}_2\uparrow$$ $$\text{Mg} + 2\text{HCl} \;\longrightarrow\; \text{MgCl}_2 + \text{H}_2\uparrow$$

Nitric Acid Exception: $\text{HNO}_3$ is a strong oxidizing agent; oxidizes $\text{H}_2$ to $\text{H}_2\text{O}$. Only $\text{Mg}$ and $\text{Mn}$ liberate $\text{H}_2$ with very dilute $\text{HNO}_3$.
Reactivity Series: $\text{K} > \text{Na} > \text{Ca} > \text{Mg} > \text{Al} > \text{Zn} > \text{Fe} > \text{Pb} > [\text{H}] > \text{Cu} > \text{Hg} > \text{Ag} > \text{Au}$.
Displacement: A more reactive metal displaces a less reactive metal from its salt solution: $$\text{Fe} + \text{CuSO}_4\text{ (blue)} \;\longrightarrow\; \text{FeSO}_4\text{ (pale green)} + \text{Cu (reddish-brown)}$$

3. Ionic Compounds & Their Properties

Formed by complete transfer of electrons from a metal atom to a non-metal atom (e.g., $\text{NaCl}, \text{MgCl}_2$).

Property	Observed Trait	Scientific Explanation
Physical State	Hard, crystalline, brittle solids.	Strong electrostatic forces between interlocked cations and anions.
Melting & Boiling Points	High ($\text{NaCl}$ MP $= 801^\circ\text{C}$).	High lattice energy required to overcome ionic attractions.
Solubility	Soluble in water; insoluble in kerosene/petrol.	Polar water molecules hydrate ions; non-polar solvents cannot overcome lattice energy.
Electrical Conductivity	Insulators in solid state; conduct in molten state or aqueous solution.	Ions fixed rigidly in solid lattice; in molten/solution state, ions become free and mobile to carry current.

4. Metallurgy: Extraction and Refining of Metals

Definitions: Mineral = Naturally occurring compound in earth's crust. Ore = Mineral from which metal is extracted profitably. Gangue = Unwanted earthy impurities (sand, clay).

Figure 27.3: Flowchart for Extraction of Metals Based on Reactivity

Extraction Methods by Reactivity Level:

Low Reactivity Metals ($\text{Hg, Cu}$): Reduced by thermal heating alone: $$2\text{HgS (Cinnabar)} + 3\text{O}_2 \;\overset{\Delta}{\longrightarrow}\; 2\text{HgO} + 2\text{SO}_2\uparrow \quad\implies\quad 2\text{HgO} \;\overset{\Delta}{\longrightarrow}\; 2\text{Hg(l)} + \text{O}_2\uparrow$$
Medium Reactivity Metals ($\text{Zn, Fe}$):
• Roasting (Sulphides in excess air): $2\text{ZnS} + 3\text{O}_2 \;\overset{\Delta}{\longrightarrow}\; 2\text{ZnO} + 2\text{SO}_2\uparrow$
• Calcination (Carbonates in limited air): $\text{ZnCO}_3 \;\overset{\Delta}{\longrightarrow}\; \text{ZnO} + \text{CO}_2\uparrow$
• Reduction by Carbon: $\text{ZnO} + \text{C} \;\overset{\Delta}{\longrightarrow}\; \text{Zn} + \text{CO}\uparrow$
• Thermite Process: $\text{Fe}_2\text{O}_3 + 2\text{Al} \;\overset{\Delta}{\longrightarrow}\; 2\text{Fe(l)} + \text{Al}_2\text{O}_3 + \text{Heat}$ (used to weld railway tracks).
High Reactivity Metals ($\text{Na, Ca, Al}$): Extracted by Electrolytic Reduction of molten chlorides/oxides (Cathode: $\text{Na}^+ + e^- \to \text{Na}$; Anode: $2\text{Cl}^- \to \text{Cl}_2 + 2e^-$).

Figure 27.4: Electrolytic Refining of Copper

Electrolytic Refining Setup:

Anode: Impure copper block ($\text{Cu} \to \text{Cu}^{2+} + 2e^-$).
Cathode: Thin strip of pure copper ($\text{Cu}^{2+} + 2e^- \to \text{Cu}$).
Electrolyte: Acidified $\text{CuSO}_4$ solution.
Anode Mud: Insoluble impurities ($\text{Ag, Au, Pt}$) settling below the anode.

5. Corrosion of Metals and Prevention

Corrosion: Deterioration of metals through atmospheric oxidation and moisture exposure.

Figure 27.5: Investigating Conditions for Rusting of Iron: Both Air and Moisture are Necessary

Rusting of Iron (Official NIOS Equation): $$4\text{Fe} + x\text{H}_2\text{O} + \text{O}_2 \;\longrightarrow\; \underset{\text{Hydrated Ferric Oxide (Rust)}}{2\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}}$$
Green Patina on Copper: $2\text{Cu} + \text{H}_2\text{O} + \text{CO}_2 + \text{O}_2 \;\longrightarrow\; \underset{\text{Basic Copper Carbonate}}{\text{CuCO}_3 \cdot \text{Cu(OH)}_2}$
Black Tarnish on Silver: $2\text{Ag} + \text{H}_2\text{S} \;\longrightarrow\; \text{Ag}_2\text{S} + \text{H}_2$
Prevention Methods: (1) Painting, (2) Oiling and Greasing, (3) Galvanization (coating with molten Zinc; sacrificial cathodic protection), (4) Alloying.

6. Alloys & Uses of Metals and Non-Metals (NIOS Syllabus)

Alloy	Composition	Key Property & Application
Steel	$\text{Fe} + \text{C} (0.1\text{--}1.5\%)$	High tensile strength; construction, infrastructure.
Stainless Steel	$\text{Fe} + \text{Cr} + \text{Ni} + \text{C}$	Does not rust; surgical tools, utensils.
Brass	$\text{Cu} + \text{Zn}$	Malleable, golden lustre; hardware, musical instruments.
Bronze	$\text{Cu} + \text{Sn}$	Corrosion resistant; statues, medals, coins.
Solder	$\text{Pb} + \text{Sn}$	Low melting point ($~183^\circ\text{C}$); welding electrical wires.
Amalgam	Any alloy with Mercury ($\text{Hg}$)	Dental fillings ($\text{Ag-Sn-Hg}$).
$22\text{ Carat Gold}$	$22\text{ parts Au} + 2\text{ parts Cu/Ag}$	Provides hardness for crafting jewellery ($24\text{ carat}$ is too soft).

Direct Industrial & Practical Uses (From NIOS Book):

Metals:
• Utensils: Iron, Aluminium (good thermal conductor).
• Electrical wires: Copper, Aluminium (high electrical conductivity, ductile).
• Heavy machinery & sheets: Iron, Aluminium (high malleability).
• Jewellery: Gold, Silver, Platinum (lustrous, non-corroding).
• Cells & batteries: Lead, Zinc.
Non-Metals:
• Fertilizers: Nitrogen ($\text{N}$) and Phosphorus ($\text{P}$) for plant growth.
• Electronics: Silicon ($\text{Si}$) for transistors, computer microchips, solar cells.
• Match Industry: White phosphorus used in match manufacture.
• Chemicals & Agriculture: Sulphur ($\text{S}$) used as fungicide, for gun powder, and manufacture of $\text{H}_2\text{SO}_4$.

7. NIOS "Test Yourself" & "Stretch Yourself" Exam Solutions

Why are metals good conductors of electricity while non-metals are not?
Answer: Metals contain a large number of free, delocalized valence electrons that can drift when a voltage is applied. Non-metals hold their valence electrons tightly in localized bonds with no free mobile electrons (except graphite).
What are the main conditions for corrosion? How to prevent it?
Answer: Simultaneous presence of both oxygen (air) and moisture (water). Prevented by painting, oiling/greasing, galvanization (zinc coating), and alloying.
How will you prove metal oxides are basic and non-metal oxides are acidic?
Answer: Dissolve magnesium oxide ($\text{MgO}$) in water to form $\text{Mg(OH)}_2$; it turns red litmus blue (basic). Dissolve sulphur dioxide ($\text{SO}_2$) in water to form $\text{H}_2\text{SO}_3$; it turns blue litmus red (acidic).
Why is Tin ($\text{Sn}$) soluble in excess $\text{NaOH}$? Give equation.
Answer: Tin is amphoteric. It reacts with strong base to form soluble sodium stannate: $$\text{Sn} + 2\text{NaOH} + \text{H}_2\text{O} \;\longrightarrow\; \text{Na}_2\text{SnO}_3 + 2\text{H}_2\uparrow$$
Why is it better to use copper than carbon in electrical wires?
Answer: Copper is highly ductile (can be drawn into flexible wires), has lower electrical resistivity, and does not break, unlike brittle graphite.
Why is aluminium used for cooking utensils?
Answer: Excellent thermal conductivity, high melting point, and self-protecting oxide layer ($\text{Al}_2\text{O}_3$) preventing corrosion.
Why does a copper coin develop a green layer in open air?
Answer: Reacts with atmospheric $\text{CO}_2$, $\text{O}_2$, and moisture to form basic copper carbonate: $$2\text{Cu} + \text{H}_2\text{O} + \text{CO}_2 + \text{O}_2 \;\longrightarrow\; \text{CuCO}_3 \cdot \text{Cu(OH)}_2 \text{ (green)}$$