Crystal Structures and Unit Cells
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Questions and Answers

What defines a crystalline solid?

  • The structure is amorphous and irregular.
  • Atoms are loosely packed without a fixed shape.
  • Atoms form a repeating pattern called a crystal lattice. (correct)
  • Atoms are arranged in a random pattern.

What is the coordination number for a Simple Cubic (SC) unit cell?

  • 4
  • 8
  • 6 (correct)
  • 12

Which type of unit cell has the highest Atomic Packing Factor (APF)?

  • Face-Centered Cubic (FCC) (correct)
  • Hexagonal Close-Packed (HCP)
  • Body-Centered Cubic (BCC)
  • Simple Cubic (SC)

What type of solid is described as having no geometric shape and weak intermolecular forces?

<p>Amorphous (A)</p> Signup and view all the answers

In a Body-Centered Cubic (BCC) unit cell, how many atoms are present per unit cell?

<p>2 (D)</p> Signup and view all the answers

Which type of crystal is composed of charged species?

<p>Ionic Crystals (C)</p> Signup and view all the answers

What characteristic differentiates anions and cations in ionic crystals?

<p>They are generally quite different in size. (C)</p> Signup and view all the answers

What is a general property of metallic crystals?

<p>They conduct both electricity and heat well. (D)</p> Signup and view all the answers

Which of the following is NOT a type of crystal mentioned?

<p>Organic (C)</p> Signup and view all the answers

Why is it difficult to measure the radius of an individual ion?

<p>It is often necessary to estimate their size. (C)</p> Signup and view all the answers

Flashcards

Crystalline Solid

A solid where atoms, ions, or molecules are arranged in an ordered, repeating pattern.

Simple Cubic (SC) Unit Cell

A unit cell where atoms are only at the corners of a cube.

Face-Centered Cubic (FCC) Unit Cell

A unit cell with atoms at the corners and centers of each face of a cube.

Body-Centered Cubic (BCC) Unit Cell

A unit cell with atoms at the corners and one at the center of a cube.

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Hexagonal Close-Packed (HCP) Unit Cell

Unit cell with atoms tightly packed in a hexagonal arrangement.

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Ionic Crystal Types

Crystals composed of charged particles (ions) with significantly different ion sizes.

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Ionic Crystal Characteristics

Ionic crystals are comprised of charged species (anions and cations), and the radii (sizes) of these ions are important for understanding their structures and stability.

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Crystal Types

Crystals are classified into ionic, covalent, molecular, and metallic types based on the forces holding the particles together.

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Metal Characteristics

Metals are elements, compounds, or alloys that conduct heat and electricity well.

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Crystal Structure and Properties

Crystal structures and properties (melting point, density, hardness) are related to the forces holding their constituent particles together.

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Study Notes

Crystal Structures

  • Crystalline solids: Atoms, ions, or molecules arranged in an ordered, repeating pattern (crystal lattice).
  • Geometric shapes, firm, rigid, incompressible.
  • Uniform, long-range intermolecular forces.
  • High melting and boiling points. Examples: Quartz, salt, diamond

Amorphous Solids

  • Random, irregular arrangement of particles.
  • Rigid structures, lack a well-defined shape.
  • Weak, variable intermolecular forces.
  • Low melting and boiling points. Examples: Glass, plastic, rubber

Unit Cells

  • Basic structural unit of a crystalline solid.
  • Lattice points are sites occupied by atoms, ions, or molecules.
  • Various types of unit cells:
    • Simple cubic (SC): Atoms at corners (coordination number 6, APF ~0.52)
    • Face-centered cubic (FCC): Atoms at corners and face centers (coordination number 12, APF ~0.74)
    • Body-centered cubic (BCC): Atoms at corners and body center (coordination number 8, APF ~0.68)
    • Hexagonal close-packed (HCP): Atoms packed in hexagonal layers (coordination number 12, APF ~0.74)

Types of Crystals

  • Classification based on forces holding particles together:
    • Ionic: Electrostatic attraction between charged species (cations and anions). Hard, brittle, high melting point, poor conductors. Examples: NaCl, LiF, MgO
    • Covalent: Covalent bonds forming an extensive three-dimensional network. Hard, high melting point, poor conductors. Examples: Diamond, Quartz
    • Molecular: Van der Waals forces and/or hydrogen bonds between molecules. Soft, low melting point, poor conductors. Examples: Argon, Carbon dioxide
    • Metallic: Metallic bonds (delocalized valence electrons). Soft to hard, low to high melting point, good conductors. Examples: Copper, Iron

Metals

  • Good conductors of heat and electricity, shiny luster, malleable and ductile.
  • Characterized by delocalized valence electrons.
  • Most metals are hard, high melting point, high density.
  • Exceptions: Mercury (liquid at room temp), Sodium and Potassium (soft)

Minerals and Ores

  • A mineral is a naturally occurring substance with a specific chemical composition and structure.
  • An ore is a mineral (or combination) from which a metal can be extracted profitably.

Metallurgy

  • Science and technology of separating metals from their ores and creating alloys.

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Description

Explore the fascinating world of crystal structures and the differences between crystalline and amorphous solids. This quiz covers unit cells, their types, and characteristics of various solid states, including examples like quartz and glass. Test your knowledge and understand the key concepts in solid-state chemistry.

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