CBSE Class 10 Science Notes: Metals and Nonmetals

Physical and Chemical Properties: Metals vs. Non-metals

This section explores the fundamental differences between metals and non-metals based on their physical and chemical behaviors. Understanding these distinctions is crucial for predicting how these elements will interact with each other and with other substances.

Physical Properties

• Lustre: Metals generally possess a shiny surface (lustrous), while non-metals are often dull (except for iodine and graphite).
• Malleability: Metals can be hammered into thin sheets (malleable). Non-metals are brittle and break easily.
• Ductility: Metals can be drawn into wires (ductile). Non-metals are not ductile.
• Conductivity: Metals are excellent conductors of heat and electricity. Non-metals are generally poor conductors (except for graphite, which conducts electricity).
• State: Most metals are solid at room temperature (except mercury). Non-metals can be solids, liquids (bromine), or gases.

Chemical Properties

• Reaction with Acids: Metals react with dilute acids to produce a metal salt and hydrogen gas (e.g., $2Na + 2HCl \rightarrow 2NaCl + H_2$). Non-metals generally do not react with dilute acids.
• Reaction with Oxygen: Most metals react with oxygen to form metal oxides (e.g., $4Fe + 3O_2 \rightarrow 2Fe_2O_3$). Non-metals also react with oxygen to form non-metal oxides (e.g., $C + O_2 \rightarrow CO_2$).

Reactivity Series

The reactivity series is a list of metals arranged in order of their decreasing reactivity. It helps us predict the outcome of various chemical reactions.

Core Principles

• The most reactive metals are at the top (e.g., Potassium, Sodium).
• The least reactive metals are at the bottom (e.g., Gold, Platinum).

Applications

• Displacement Reactions: A more reactive metal can displace a less reactive metal from its salt solution. (e.g., $Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$)
• Reaction with Water/Acids: More reactive metals react vigorously with water or acids, while less reactive metals react slowly or not at all.

Ionic Compounds

Ionic compounds are formed through the transfer of electrons between atoms, resulting in the formation of ions and electrostatic attraction.

Formation of Ionic Bonds

An ionic bond forms when a metal atom (which easily loses electrons) transfers one or more electrons to a non-metal atom (which easily gains electrons). This transfer creates positively charged ions (cations) and negatively charged ions (anions), which are then held together by strong electrostatic forces.

Properties of Ionic Compounds

• Crystalline Structure: Ionic compounds form a regular, repeating three-dimensional structure (crystal lattice).
• High Melting and Boiling Points: Due to the strong electrostatic forces between ions, a lot of energy is required to break these bonds.
• Solubility: Many ionic compounds are soluble in polar solvents like water, as water molecules can surround and separate the ions.
• Conductivity: They conduct electricity when dissolved in water or in molten state because the ions are free to move and carry charge. In the solid state, they don’t conduct electricity.

Examples: Sodium chloride (NaCl), Magnesium oxide (MgO)

Basic Metallurgical Processes

This section outlines the processes involved in extracting a metal from its ore.

Ore to Metal Steps

1. Concentration/Ore Dressing: Removing unwanted impurities (gangue) from the ore. Methods include:
   • Hydraulic washing
   • Magnetic separation
   • Froth floatation
2. Extraction of Metal: This involves converting the concentrated ore into the metal. This can be achieved through:
   • Roasting: Heating the ore in the presence of oxygen, to convert it to oxide (for sulfide ores).
   • Calcination: Heating the ore in the absence of oxygen to convert it to oxide (for carbonate ores).
   • Reduction: Using a reducing agent (e.g., carbon, carbon monoxide, or a more reactive metal) to remove oxygen from the metal oxide. This happens at high temperatures.
3. Refining: Further purification of the extracted metal to remove any remaining impurities. Methods include:
   • Electrolytic refining
   • Distillation
   • Zone refining

Corrosion

Corrosion is the gradual deterioration of a material, usually a metal, due to a chemical reaction with its surroundings.

What Causes Corrosion?

Corrosion is often an electrochemical process. Metals react with substances in the environment (e.g., oxygen, water, acids, and salts), leading to the formation of metal oxides or other compounds and the loss of the metal.

Prevention Methods

• Painting: Applying a protective coating to isolate the metal from the environment.
• Galvanizing: Coating iron with a layer of zinc, which protects the iron because zinc corrodes preferentially (sacrificial protection).
• Electroplating: Depositing a thin layer of a more resistant metal (e.g., chromium, nickel) on the surface of the object.
• Alloying: Creating alloys such as stainless steel that are resistant to corrosion.
• Using corrosion inhibitors: Adding chemicals to the environment to slow down the corrosion process.