PART 3 GIANT COVALENT BONDING PROPERTIES

Giant Covalent Structures Properties

  • Overview of giant covalent structures and their properties.

Understanding Giant Covalent Compounds

  • Purpose: To explore and understand the properties of giant covalent compounds.

Covalent Compounds

  • Definition: Formed between non-metal atoms.

  • Characteristics of Bonds: Each bond consists of a shared pair of electrons, resulting in very strong connections.

  • Two Main Types:

    • Simple molecules

    • Giant covalent structures

Simple Molecules – Recap

  • Structure: Contains few atoms held by strong covalent bonds.

  • Example: Carbon dioxide (CO2) consists of one carbon atom and two oxygen atoms.

  • Intermolecular Forces: Weak attracting forces between molecules, allowing them to break easily.

  • Illustration: O O O C O H O H

    • Oxygen (O), Water (H2O), and Carbon Dioxide (CO2).

Simple Molecular Substances Properties – Recap

  • Physical Properties:

    • Low melting and boiling points due to weak intermolecular forces that break down easily.

    • Non-conductive because they lack free electrons and overall electric charge.

    • Typically soft and brittle solids that shatter upon impact.

    • Insoluble in water but soluble in other solvents (e.g., petrol).

    • At room temperature, simple molecular substances exist as gases, liquids, or solids with low melting and boiling points.

Allotropes

  • Definition: Different physical forms of the same element.

  • Common Characteristics: Same chemical properties due to equal electron numbers.

  • Physical Properties Variation: Different bonding structures lead to different characteristics.

  • Examples: Carbon allotropes include diamond and graphite.

Giant Covalent Structures

  • Composition: Contain numerous non-metal atoms joined by covalent bonds.

  • Formation: Atoms typically form giant regular lattices, resulting in extremely strong structures.

  • Examples of Carbon Allotropes: Diamond and graphite showcase different molecular structures.

    • Graphite (left) and diamond (right) differ in structure despite being carbon allotropes.

Giant Covalent Structures of Carbon

  • Characteristics: Millions of atoms bonded through covalent bonds form giant structures, not simple molecules.

  • Properties: Strong covalent bonds result in very high melting and boiling points, and most giant covalent structures are hard yet brittle.

Diamond

  • Structure: Each carbon atom bonds with four other carbon atoms, creating a giant covalent structure.

  • Bonding: All outer shell electrons are utilized in covalent bonds, resulting in extremely strong bonding throughout.

  • Properties:

    • Very hard (hardest naturally occurring substance)

    • High melting point

    • Non-conductive due to lack of charged particles.

Graphite

  • Structure: Each carbon atom bonds with three others, with one free valence electron per atom.

  • Layer Formation: Carbon atoms form rings of six, creating layers held together by weak forces, allowing them to slide over one another.

  • Properties:

    • Softer than diamond

    • Conductive due to free movement of electrons between layers.

    • Applications: Used in pencils and as a lubricant.

Other Carbon Allotropes

  • Buckminsterfullerene: Different from giant covalent structures; classified as a giant molecule.

  • Structure: Contains 60 carbon atoms, each bonding with three others, forming a configuration of 12 pentagons and 20 hexagons—commonly referred to as 'bucky balls.'

Silica - The Giant Covalent Compound

  • Overview: Sand is an impure form of silicon dioxide (quartz).

  • Structure Similarity: Silica's structure resembles diamond, resulting in high hardness and melting point, but composed of silicon and oxygen atoms.

  • Bonding: Each silicon atom is bonded to four oxygen atoms, and vice versa.

  • Applications: A semiconductor, its versatility makes it immensely useful in electronics, particularly in transistors.

Summary - Giant Covalent Properties

  • Key Properties:

    • Very high melting points due to numerous strong covalent bonds that need to be broken (e.g., graphite melting point exceeds 3,600ºC).

    • Variable conductivity: Diamond (non-conductive), graphite (conductive), and silica (semiconductive).

    • Very hard, with the exception of graphite, which is softer.

    • Generally chemically unreactive.

Summary of Uses

  • Graphite: Used in various inventions and products such as pencils.

  • Diamonds: Notable for jewelry, they have unique properties including durability and sharpness—warning includes potential staining on clothing.