CBSE Class 10 Science – Chapter 3: Metals and Non-metals
Introduction
Metals and non-metals are two major categories of elements that differ significantly in their physical and chemical properties. Metals are known for their luster, malleability, ductility, and good conductivity, while non-metals exhibit contrasting properties. Understanding these differences is crucial for various applications in daily life and industries.
Physical Properties of Metals
- Lustre: Metals possess a shiny surface when freshly cut, polished, or scratched, known as metallic lustre.
- Malleability: Metals can be hammered or rolled into thin sheets without breaking.
- Ductility: Metals can be drawn into thin wires.
- Conductivity: Metals are excellent conductors of heat and electricity.
- Hardness: Most metals are hard, making them suitable for construction and manufacturing tools.
- Sonorous: Metals produce a ringing sound when struck.
Physical Properties of Non-metals
- Lustre: Non-metals do not have a shiny appearance; they are generally dull.
- Malleability: Non-metals are brittle and cannot be beaten into sheets.
- Ductility: Non-metals cannot be drawn into wires; they break when stretched.
- Conductivity: Non-metals are poor conductors of heat and electricity, with the exception of graphite.
- Hardness: Non-metals are usually soft, though diamond, a form of carbon, is the hardest known natural substance.
- Sonorous: Non-metals do not produce a ringing sound when struck; they are non-sonorous.
Chemical Properties of Metals
Reaction with Oxygen
Metals react with oxygen to form metal oxides, which are generally basic in nature.
4Na + O2 → 2Na2O
2Mg + O2 → 2MgO
Reaction with Water
Metals react with water to form metal hydroxides and hydrogen gas. The reactivity with water varies among metals.
2Na + 2H2O → 2NaOH + H2 ↑
Ca + 2H2O → Ca(OH)2 + H2 ↑
Reaction with Acids
Metals react with acids to produce salt and hydrogen gas.
Zn + 2HCl → ZnCl2 + H2 ↑
Mg + 2HCl → MgCl2 + H2 ↑
Reaction with Bases
Some metals, like aluminum and zinc, react with strong bases to form complex compounds.
2Al + 2NaOH + 6H2O → 2Na[Al(OH)4] + 3H2 ↑
Zn + 2NaOH → Na2[Zn(OH)4] + H2 ↑
Metal Oxides
Basic Oxides
Metal oxides that dissolve in water to form basic solutions.
Na2O + H2O → 2NaOH
Amphoteric Oxides
Metal oxides that can react with both acids and bases to form salts and water.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2O
Reactivity Series
| Metal | Reactivity |
|---|---|
| Potassium (K) | Highly Reactive |
| Sodium (Na) | Highly Reactive |
| Calcium (Ca) | Very Reactive |
| Magnesium (Mg) | Very Reactive |
| Aluminum (Al) | Reactive |
| Zinc (Zn) | Moderately Reactive |
| Iron (Fe) | Moderately Reactive |
| Lead (Pb) | Less Reactive |
| Copper (Cu) | Less Reactive |
| Silver (Ag) | Least Reactive |
| Gold (Au) | Least Reactive |
Chemical Properties of Non-metals
Reaction with Oxygen
Non-metals react with oxygen to form acidic or neutral oxides.
C + O2 → CO2
S + O2 → SO2
Reaction with Water
Non-metals generally do not react with water. However, chlorine reacts with water to form a mixture of hydrochloric acid and hypochlorous acid.
Cl2 + H2O → HCl + HClO
Reaction with Acids
Non-metals do not react with dilute acids. However, concentrated acids can oxidize some non-metals.
Reaction with Bases
Non-metals generally do not react with bases, but some reactions can occur under specific conditions.
Ionic and Covalent Bonds
Ionic Bonds
Ionic bonds are formed by the transfer of electrons from a metal to a non-metal, resulting in the formation of positively charged metal ions (cations) and negatively charged non-metal ions (anions).
Na → Na+ + e–
Cl + e– → Cl–
Na+ + Cl– → NaCl
Covalent Bonds
Covalent bonds are formed by the sharing of electrons between non-metals. This bond type is found in molecules like water (H2O) and carbon dioxide (CO2).
2H + O → H2O
Occurrence and Extraction of Metals
Occurrence
Metals are found in the earth’s crust as minerals and ores. Some metals are found in their native state (e.g., gold, silver), while others are found as compounds (e.g., iron, aluminum).
Extraction
- Concentration of Ore: The process of removing impurities from the ore to increase the concentration of the desired metal.
- Reduction: The process of extracting metal from its concentrated ore. This can involve chemical reduction, electrolytic reduction, or thermal reduction.
- Refining: The final step to obtain pure metal from the crude metal obtained from reduction. Techniques include electrolytic refining, distillation, and zone refining.
| Metal | Method of Extraction |
|---|---|
| Iron (Fe) | Blast Furnace (Reduction) |
| Aluminum (Al) | Electrolysis of Alumina |
| Copper (Cu) | Roasting and Reduction |
| Zinc (Zn) | Roasting and Electrolysis |
| Gold (Au) | Cyanide Process |
