Metals and Non Metals

Overview & Fundamental Concept

Complete AISSEE Class 9 General Science guide for Metals and Non Metals (Topic 8). Covers pointwise physical and chemical comparisons, reactivity series mnemonics, displacement reaction equations, solved exam models, and 10 practice drills.

• Malleability: The property of metals by which they can be beaten into very thin sheets with a hammer without breaking. Gold (Au) and Silver (Ag) are the most malleable metals known. (Aluminium foils are used for wrapping food; silver foils / vark for decorating sweets). Non-metals are brittle and shatter into powder when hammered.
• Ductility: The property of metals by which they can be drawn into very thin wires. Gold is the most ductile metal (1 gram of gold can be drawn into a wire ~2 km long!). Non-metals are strictly non-ductile.
• Sonorousness: Metals produce a characteristic ringing sound when struck with a hard object (used for making temple bells, school bells, guitar strings). Non-metals are non-sonorous.
• Metallic Lustre: Freshly cut surfaces of metals have a bright shining appearance. Non-metals are generally dull.
• Thermal & Electrical Conductivity: Metals are excellent conductors of heat and electricity due to free mobile valence electrons. Silver (Ag) is the best conductor of electricity, followed by Copper (Cu). Non-metals are poor conductors (insulators).
• Famous AISSEE Anomalous Exceptions (High-Yield):
  • Liquid Metal: Mercury (Hg) is the only metal that is liquid at room temperature (used in clinical thermometers).
  • Liquid Non-Metal: Bromine (Br₂) is the only non-metal that is liquid at room temperature (reddish-brown fuming liquid).
  • Soft Metals: Sodium (Na) and Potassium (K) are soft alkali metals with low densities that can be cut easily with an ordinary butter knife.
  • Low Melting Point Metals: Gallium (Ga) and Caesium (Cs) have melting points so low (29.7°C and 28.4°C) that they melt readily when placed on the palm of a human hand.
  • Lustrous Non-Metal: Iodine (I₂) is a non-metal that possesses a bright shining metallic lustre.
  • Hardest Natural Substance: Diamond (an allotrope of the non-metal Carbon) is the hardest known natural substance and has an extremely high melting point.
  • Conducting Non-Metal: Graphite (another allotrope of Carbon) is a good conductor of electricity due to free delocalized electrons in its hexagonal sheets (used for dry cell electrodes and pencil leads).

• 1. Reaction with Oxygen:
  • Metals react with oxygen to form Metallic Oxides, which are BASIC in nature.
  $$\text{Metal} + \text{Oxygen} \longrightarrow \text{Basic Metal Oxide}$$
  • Example 1: Burning magnesium ribbon in air forms magnesium oxide ash ($2Mg + O_2 \rightarrow 2MgO$). Dissolving $MgO$ in water forms magnesium hydroxide [$Mg(OH)_2$], which turns RED litmus paper BLUE.
  • Example 2: Rusting of Iron: Iron reacts with oxygen and moisture to form hydrated ferric oxide ($4Fe + 3O_2 + 2xH_2O \rightarrow 2Fe_2O_3 \cdot xH_2O$). Rust is basic and turns red litmus blue.
  • Amphoteric Oxides: Oxides of Aluminium ($Al_2O_3$) and Zinc ($ZnO$) react with BOTH acids and strong bases to produce salt and water.
• Non-Metals Reaction with Oxygen:
  • Non-metals react with oxygen to form Non-Metallic Oxides, which are ACIDIC in nature.
  $$\text{Non-Metal} + \text{Oxygen} \longrightarrow \text{Acidic Non-Metal Oxide}$$
  • Example: Burning sulphur in air forms sulphur dioxide gas ($S + O_2 \rightarrow SO_2$). When dissolved in water, it forms sulphurous acid ($H_2SO_3$), which turns BLUE litmus paper RED:
  $$SO_2 + H_2O \longrightarrow H_2SO_3 \quad (\text{Sulphurous Acid})$$
  • Neutral Oxides: Carbon monoxide ($CO$), Water ($H_2O$), Nitrous oxide ($N_2O$) are neutral non-metallic oxides (do not affect litmus).

• 2. Reaction with Water:
  • Sodium & Potassium: React explosively with cold water, evolving hydrogen gas which catches fire immediately with a lilac/yellow flame ($2Na + 2H_2O \rightarrow 2NaOH + H_2 \uparrow + \text{Heat}$).
  • Calcium: Reacts less violently with cold water; bubbles of $H_2$ stick to its surface so it floats.
  • Magnesium: Reacts very slowly with cold water, but reacts rapidly with boiling water or steam.
  • Iron & Zinc: Do not react with cold or hot water; react only with red-hot steam.
  • Copper, Silver, Gold, Platinum: Do NOT react with water or steam at all.
  • Non-Metals: Generally do not react with water.
• 3. Reaction with Dilute Acids:
  • Metals placed above hydrogen in the reactivity series displace hydrogen from dilute hydrochloric acid ($HCl$) or dilute sulphuric acid ($H_2SO_4$) to form metal salt and Hydrogen gas ($H_2$).
  $$\text{Metal} + \text{Dilute Acid} \longrightarrow \text{Metal Salt} + \text{Hydrogen Gas } (H_2 \uparrow)$$
  • The 'POP' Sound Test: Bringing a burning matchstick near the mouth of the test tube extinguishes the flame and burns the gas with a distinctive 'POP' sound, proving the presence of hydrogen gas.
  • Copper, Silver, and Gold do NOT react with dilute $HCl$ or dilute $H_2SO_4$ to evolve hydrogen gas.
• The Official Reactivity (Activity) Series of Metals: Arrangement of metals in the order of their decreasing chemical reactivity:
  $$\mathbf{K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au}$$

• Displacement Reaction: A chemical reaction in which a more reactive metal displaces a less reactive metal from its aqueous salt solution.
  $$\text{More Reactive Metal} + \text{Salt of Less Reactive Metal} \longrightarrow \text{Salt of More Reactive Metal} + \text{Less Reactive Metal}$$
• Classic AISSEE Displacement Examples:
  • 1. Iron in Copper Sulphate:
  $$Fe \text{ (Grey)} + CuSO_4 \text{ (Blue)} \longrightarrow FeSO_4 \text{ (Pale Green)} + Cu \text{ (Reddish-brown)}$$
   Iron is more reactive than copper; it displaces copper, turning the solution green and depositing red copper on the nail.
  • 2. Zinc in Copper Sulphate:
  $$Zn + CuSO_4 \text{ (Blue)} \longrightarrow ZnSO_4 \text{ (Colorless)} + Cu \text{ (Red)}$$
   Zinc is more reactive than copper; it completely decolourizes the blue solution.
  • 3. Reverse Reaction Fails: Adding copper turnings to zinc sulphate ($Cu + ZnSO_4 \rightarrow \text{NO REACTION}$) or ferrous sulphate ($Cu + FeSO_4 \rightarrow \text{NO REACTION}$) produces zero change because Copper is LESS reactive than Zinc and Iron.
• Practical Industrial Uses:
  • Copper & Aluminium: Electrical transmission wiring, utensils, automotive radiators.
  • Iron: Construction beams, bridges, railway tracks, machinery (cast iron, wrought iron, steel alloys).
  • Gold & Silver: Jewelry, coinage, high-end electronics contacts, decorative reflective mirrors.
  • Zinc: Galvanisation (protective coating on iron sheets to prevent rust).
  • Non-Metals Uses:
   • Oxygen: Respiration of living beings and combustion of fuels.
   • Nitrogen: In fertilizers (Urea) to enhance plant growth; inert packaging gas in potato chip packets to prevent rancidity.
   • Chlorine: Water purification disinfectant (kills microbial pathogens).
   • Iodine: Applied on wounds as an antiseptic (Tincture of Iodine: 2–3% solution in alcohol-water).
   • Sulphur: Vulcanisation of rubber, fireworks, and manufacturing sulfuric acid ($H_2SO_4$).