Module 4

• Expectations for the module include describing the structure of crystalline and amorphous solids, differentiating between them, and recognizing their important applications
• The Pretest in the module assesses the learners' prior knowledge about the lesson on crystalline and amorphous solids
• The Recap section evaluates the effect of intermolecular forces on the properties of solids, focusing on viscosity, vapor pressure, surface tension, molar heat of vaporization, and strong vs. weak intermolecular forces
• The Lesson in the module contrasts and compares different types of solids, specifically crystalline and amorphous solids
• Crystalline solids are composed of small crystals with a definite geometrical shape, making them rigid and incompressible
• Crystalline solids have a repeated pattern of arrangement of particles with long-range order, indicating their sharp melting point and definite heat of fusion
• The unit cell is the basic repeating structural unit of crystalline solids, with atoms or molecules represented by lattice points arranged identically
• The stable crystal structure of crystalline solids is due to intermolecular forces like ionic forces, covalent bonds, London dispersion forces, and hydrogen forces
• The structure and properties of crystals are determined by the types of intermolecular forces that hold the particles together
• Types of crystalline solids include ionic crystals, which are composed of charged particles with strong electrostatic interactions, resulting in hard solids with high melting points
• Hard solids have numerous electrostatic attractions throughout the crystal, making them hard
• Hard crystals have high melting points and become good conductors once they melt and turn into a liquid state
• Solid-state and molten state crystals in this type are poor electrical conductors due to the firm hold of ions with no large space for movement
• Ionic crystals are brittle and break when deformed, causing attractive forces to be broken
• Metallic crystals are held together by electrostatic force between cations and delocalized electrons
• Delocalized electrons in metallic crystals can freely move across the entire metal, making them good conductors of electricity and heat
• Metallic crystals are dense, with closely packed atoms leading to strong attractions and high melting points
• Malleability in metallic crystals allows atoms to roll over each other without breaking the metallic bond
• Molecular crystals are crystalline solids where lattice points are occupied by molecules with weak intermolecular forces
• Molecular crystals have low melting points due to weak intermolecular forces and are soft and brittle
• Covalent crystals have atoms bonded covalently with strong intermolecular forces, resulting in very high melting points
• Covalent crystals do not have charged particles available to move through the crystals, making them poor conductors of electricity
• Amorphous solids lack a well-defined shape or regular three-dimensional arrangement of atoms
• Amorphous solids do not have sharp melting points and soften slowly over a wide temperature range
• Amorphous solids have weaker intermolecular forces than crystalline solids, leading to different amounts of thermal energy needed to overcome interactions