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Science and TechnologySEE 2075

a) What is meant by the term "metallic bond"? [1] b) Write the characteristics of metallic bonds. [2] c) Write the examples of metallic bonding. [2]

5

Answer

· Based on the official syllabus and past papers
Updated
Na11p 12nNa: 2, 8, 1
Sodium atom: 11 electrons (2 in the 1st shell, 8 in the 2nd, 1 in the 3rd outermost shell) before bonding.

a) Metallic Bond

A metallic bond is a type of chemical bonding that occurs between metal atoms in a metallic lattice. It arises due to the electrostatic attraction between positively charged metal ions (cations) and a sea of delocalized electrons (free electrons) that move freely throughout the metal structure. These delocalized electrons are shared among all the metal atoms, forming a "sea of electrons" that holds the metal ions together.

structure
Sea of electrons in metallic bonding (simplified: delocalized electrons shared among Na⁺ ions)

b) Characteristics of Metallic Bonds

Metallic bonds exhibit the following key characteristics:

  1. Non-directional Bonding

    • The bonding is non-directional because the delocalized electrons are free to move in all directions within the metal lattice.
    • This gives metals their malleability (can be hammered into sheets) and ductility (can be drawn into wires).

  2. High Electrical and Thermal Conductivity

    • The free-moving electrons allow metals to conduct electricity and heat efficiently.
    • Example: Copper is used in electrical wiring due to its high conductivity.

  3. Lustrous (Shiny) Appearance

    • The delocalized electrons reflect light, giving metals their characteristic metallic luster.

  4. High Melting and Boiling Points

    • Strong electrostatic forces between metal ions and electrons require high energy to break, leading to high melting and boiling points.
    • Example: Tungsten (used in light bulb filaments) has a very high melting point (~3422°C).

  5. Variable Bond Strength

    • The bond strength varies among metals. Transition metals (e.g., iron, copper) have stronger metallic bonds compared to alkali metals (e.g., sodium, potassium), which are softer and have lower melting points.

  6. Good Mechanical Strength

    • Metals are generally strong and rigid due to the strong electrostatic forces in the lattice.
    • Alloys (mixtures of metals) are even stronger (e.g., steel = iron + carbon).

c) Examples of Metallic Bonding

Metallic bonding is observed in all metallic elements and their alloys. Some common examples include:

Element/Alloy Type Key Property Due to Metallic Bonding
Sodium (Na) Alkali Metal Soft, low melting point (97.8°C), good conductor.
Copper (Cu) Transition Metal High electrical conductivity, used in wiring.
Iron (Fe) Transition Metal Strong, used in construction and machinery.
Aluminum (Al) Post-transition Metal Lightweight, corrosion-resistant, used in aircraft.
Gold (Au) Transition Metal Highly malleable, ductile, used in jewelry and electronics.
Steel (Fe + C) Alloy Extremely strong, used in buildings and tools.
Brass (Cu + Zn) Alloy Corrosion-resistant, used in musical instruments.
Mercury (Hg) Liquid Metal Only metal liquid at room temperature, used in thermometers.

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