Download Science chemistry ch 3 notes and more Study notes Earth science in PDF only on Docsity!
Chapter 3: Metals and Non-Metals
1. Physical Properties of Metals and Non-Metals
Properties of Metals:
Metallic Lustre: Metals, in their pure state, have a shining reflective surface (e.g., Gold, Silver). Hardness: They are generally mechanically hard. Exceptionally, alkali metals like Lithium, Sodium, and Potassium are so soft that they can be neatly sliced with a knife. Malleability: The chemical property by which metals can be hammered and beaten into thin sheets. Gold and Silver are the most malleable elements. Ductility: The ability of metals to be stretched into thin wires. Gold is exceptionally ductile (1g of gold can produce a 2km long wire). Conductivity: Metals are superb thermal and electrical conductors.
- Silver and Copper represent the top heat conductors.
- Lead and Mercury act as poor thermal conductors. Melting & Boiling Points: They possess high melting parameters. However, Gallium and Cesium have extremely low melting points; they will liquify just from your body heat if placed on your palm. Sonorous: Metals emit a deep ringing acoustic sound when struck against solid objects.
Properties of Non-Metals:
They exist freely as solids, liquids, or gases. Bromine stands as the unique non-metal that is a liquid at room temp. They exhibit a dull appearance. Exception: Iodine is a non-metal that possesses a shiny, lustrous appearance. They are poor electric/thermal conductors. Exception: Graphite (a structural allotrope of carbon) efficiently conducts electrical current. They are highly brittle and completely lack malleable or ductile traits. Diamond (carbon allotrope) is the hardest known natural structural substance on Earth and features an incredibly high melting threshold.
Complete Comprehensive English Study Notes | Class 10 Chemistry
2. Chemical Properties of Metals
I. Reaction of Metals with Oxygen (Air)
Metals burn in or react with oxygen to yield Basic Metal Oxides.
Metal + Oxygen → Metal Oxide
4Al(s) + 3O₂(g) → 2Al₂O₃(s) [Aluminium Oxide]
2Cu(s) + O₂(g) → 2CuO(s) [Copper(II) Oxide - Black Layer]
Amphoteric Oxides: Metal oxides that chemically react with both acids and bases to generate salt and water are called amphoteric oxides. Highly important examples include Aluminium Oxide ( Al₂O₃ ) and Zinc Oxide ( ZnO ).
- Acid Reaction: Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
- Base Reaction: Al₂O₃ + 2NaOH → 2NaAlO₂ [Sodium Aluminate] + H₂O
II. Reaction of Metals with Water
Metal + Water → Metal Oxide/Hydroxide + Hydrogen Gas
Sodium (Na) & Potassium (K): React violently with cold water. The energy release is so rapid that the generated H₂ gas instantly ignites. Therefore, they are safely preserved under kerosene oil. Calcium (Ca): Reacts moderately with cold water. The metal fragments begin to float because the evolving hydrogen gas bubbles adhere to its surface. Magnesium (Mg): Fails to react with cold water; it reacts only with hot water and floats due to adhering gas bubbles. Aluminium (Al), Iron (Fe), & Zinc (Zn): Do not react with cold or hot water. They react exclusively with steam.
3Fe(s) + 4H₂O(g) &xrightarrow{steam} Fe₃O₄(s) + 4H₂(g)
Lead (Pb), Copper (Cu), Silver (Ag), and Gold (Au) fail to react with water under any conditions.
Electrical Conductivity:
- In solid state , they do not conduct because ions are fixed tightly inside a rigid lattice.
- In molten or dissolved state , they conduct efficiently because free ions are liberated to move and act as charge carriers.
5. Metallurgy (Extraction of Metals)
Ores represent natural mineral deposits containing high concentrations of specific metals that can be mined and processed profitably. Gangue defines the raw sand, soil, and earthly impurities mixed into mined ore.
Conversion of Ores to Metal Oxides:
Roasting: Used primarily for sulfide ores. The ore is heated intensely in the presence of excess air.
2ZnS(s) [Zinc Blende] + 3O₂(g) &xrightarrow{Heat} 2ZnO(s) + 2SO₂(g)
Calcination: Used primarily for carbonate ores. The ore is heated intensely in limited air or total absence of oxygen.
ZnCO₃(s) [Calamine] &xrightarrow{Heat} ZnO(s) + CO₂(g)
Chemical Reduction: The intermediate metal oxides are reduced to raw metal forms using standard reducing components like Carbon (Coke).
ZnO(s) + C(s) → Zn(s) + CO(g)
Thermite Reaction: A highly exothermic reaction where active Aluminium powder acts as a reducing agent to displace low-activity iron from its oxide. The heat generated is so high that the metal emerges in a liquid molten phase.
Fe₂O₃(s) + 2Al(s) → 2Fe(l) [Molten Iron] + Al₂O₃(s) + Heat
- Application: Used on-site to weld and fuse broken railway tracks or damaged heavy machine joints.
Electrolytic Refining of Metals:
Crude, unrefined copper or other metals are purified via an electrolytic cell matrix:
Anode (+): Formed from a thick slab of impure crude metal. Cathode (-): Formed from a thin, clean strip of pure metal.
Electrolyte: An aqueous solution of the metal salt (e.g., Acidified Copper Sulfate solution). Insoluble leftover impurities precipitate straight down below the anode block, collecting as Anode Mud.
6. Corrosion and its Prevention
Rusting of Iron: Iron reacts with moist oxygen to form a flaky brown crust layer of hydrated ferric oxide ( Fe₂O₃ · xH₂O ). Tarnishing of Silver: Silver reacts with ambient sulfur traces to grow a black surface layer of Silver Sulfide (Ag₂S). Copper Green Coating: Copper reacts with moist carbon dioxide to form a distinctive green coat of Basic Copper Carbonate [CuCO₃ · Cu(OH)₂].
Prevention Methods:
Barrier Protections: Painting, oiling, or greasing completely halts exposure to moisture and oxygen. Galvanization: Coating iron or steel objects with a thin sacrificial protective skin of Zinc (Zn). Zinc shields the iron because it is structurally more reactive and will oxidize first, even if scratched. Alloying: Combining multiple metals into homogeneous structures to permanently alter and upgrade their physical/chemical stamina.
- Stainless Steel: Iron + Nickel (Ni) + Chromium (Cr). Extremely tough and fully rustless.
- Brass / Bronze: Brass ( Cu + Zn ) | Bronze ( Cu + Sn ).
- Solder: Lead and Tin alloy ( Pb + Sn ). It features a very low melting temperature and is widely used to weld circuit connections.
- Amalgam: Any dynamic metallic alloy where Mercury (Hg) is used as a core component.
