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What is the basic structural unit of a crystalline solid?
What is the basic structural unit of a crystalline solid?
A unit cell
What is a lattice point?
What is a lattice point?
A lattice point represents an atom, ion, or molecule in a unit cell.
Which of the following are characteristics of crystalline solids?
Which of the following are characteristics of crystalline solids?
Which of the following are examples of crystalline solids?
Which of the following are examples of crystalline solids?
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What are the characteristics of amorphous solids?
What are the characteristics of amorphous solids?
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Which of the following are examples of amorphous solids?
Which of the following are examples of amorphous solids?
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What are the three common types of unit cells?
What are the three common types of unit cells?
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The simple cubic (SC) crystal structure has atoms located only at the corners of a cube.
The simple cubic (SC) crystal structure has atoms located only at the corners of a cube.
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Which of the following metals have a face-centered cubic (FCC) crystal structure?
Which of the following metals have a face-centered cubic (FCC) crystal structure?
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What is the relationship between the cube edge length ("a") and the atomic radius (R) in a face-centered cubic (FCC) crystal structure?
What is the relationship between the cube edge length ("a") and the atomic radius (R) in a face-centered cubic (FCC) crystal structure?
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How many atoms are present in a face-centered cubic (FCC) unit cell?
How many atoms are present in a face-centered cubic (FCC) unit cell?
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What is the coordination number in a face-centered cubic (FCC) crystal structure?
What is the coordination number in a face-centered cubic (FCC) crystal structure?
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What is the atomic packing factor (APF) for a face-centered cubic (FCC) crystal structure?
What is the atomic packing factor (APF) for a face-centered cubic (FCC) crystal structure?
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What is the relationship between the unit cell length ("a") and the atomic radius (R) in a body-centered cubic (BCC) crystal structure?
What is the relationship between the unit cell length ("a") and the atomic radius (R) in a body-centered cubic (BCC) crystal structure?
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How many atoms are present in a body-centered cubic (BCC) unit cell?
How many atoms are present in a body-centered cubic (BCC) unit cell?
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What is the coordination number in a body-centered cubic (BCC) crystal structure?
What is the coordination number in a body-centered cubic (BCC) crystal structure?
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The atomic packing factor (APF) for BCC is lower than for FCC.
The atomic packing factor (APF) for BCC is lower than for FCC.
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What is the final common metallic crystal structure?
What is the final common metallic crystal structure?
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How many atoms are present in a hexagonal close-packed (HCP) unit cell?
How many atoms are present in a hexagonal close-packed (HCP) unit cell?
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Which of the following metals have a hexagonal close-packed (HCP) crystal structure?
Which of the following metals have a hexagonal close-packed (HCP) crystal structure?
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What is the formula for calculating the density of a metallic solid, considering its crystal structure?
What is the formula for calculating the density of a metallic solid, considering its crystal structure?
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What are the four main types of crystals?
What are the four main types of crystals?
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Which of the following are characteristics of ionic crystals?
Which of the following are characteristics of ionic crystals?
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Ionic crystals are good conductors of electricity in their solid state.
Ionic crystals are good conductors of electricity in their solid state.
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Which of the following are examples of ionic crystals?
Which of the following are examples of ionic crystals?
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Covalent crystals are held together by covalent bonds.
Covalent crystals are held together by covalent bonds.
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Which of the following are examples of covalent crystals?
Which of the following are examples of covalent crystals?
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Diamond is a good conductor of heat.
Diamond is a good conductor of heat.
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Graphite is a good conductor of electricity.
Graphite is a good conductor of electricity.
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Which of the following forces are responsible for holding molecules together in molecular crystals?
Which of the following forces are responsible for holding molecules together in molecular crystals?
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Which of the following are examples of molecular crystals?
Which of the following are examples of molecular crystals?
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Molecular crystals have lower melting points compared to ionic and covalent crystals.
Molecular crystals have lower melting points compared to ionic and covalent crystals.
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Metallic crystals are usually body-centered cubic, face-centered cubic, or hexagonal close-packed structures.
Metallic crystals are usually body-centered cubic, face-centered cubic, or hexagonal close-packed structures.
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What are the properties of metallic crystals?
What are the properties of metallic crystals?
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Metallic crystals are good conductors of heat because of the bonding electrons which are localized.
Metallic crystals are good conductors of heat because of the bonding electrons which are localized.
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Study Notes
General Chemistry - SCI 401
- This course covers General Chemistry.
- Specific topics include Chemistry of Engineering Materials, Basic Concepts of Crystal Structures.
Chemistry of Engineering Materials: Basic Concepts of Crystal Structures
- Topics include Crystal Structures, Unit Cells, Density Computations, Types of Crystals, and Amorphous Solids.
Crystal Structures
- Atoms, ions, or molecules are arranged in an ordered and repeating pattern, a crystal lattice.
- These structures have defined geometric shapes.
- These are firm, rigid, and incompressible.
- The intermolecular forces are uniform, long-range, and in an orderly pattern.
- They have high melting and boiling points.
Unit Cells
- A unit cell is the basic repeating unit of a crystalline solid.
- Each sphere in a unit cell diagram represents an atom, ion, or molecule and is called a lattice point.
- Unit cells can be categorized as simple cubic, face-centered cubic, body-centered cubic, tetragonal, orthorhombic, rhombohedral, monoclinic, or triclinic, hexagonal.
Density Computations
- The theoretical density of a crystal can be calculated using the formula ρ= nA / VcNA
- where:
- ρ= theoretical density
- n=number of atoms associated with each unit cell.
- A=atomic weight
- Vc= volume of the unit cell
- NA=Avogadro's number.
Types of Crystals
- Crystals can be classified as Ionic, Covalent, Molecular, and Metallic based on the forces holding the particles together.
Ionic Crystals
- Ionic crystals consist of charged species (anions and cations) with significant differences in size.
- Ionic radii are important for understanding crystal structure and stability.
- NaCl (table salt) is an example, showing a face-centered cubic lattice.
- Ionic crystals generally have high melting points due to strong electrostatic attraction between ions.
- They are typically brittle and poor conductors of heat and electricity in the solid state, but conduct electricity when molten or dissolved in water.
Covalent Crystals
- Covalent crystals are held together by covalent bonds in a three-dimensional network
- Diamond and graphite (two allotropes of carbon) are examples of covalent crystals.
- Diamond has a high melting point, is hard, and an excellent thermal conductor.
- Graphite is a good conductor of electricity along the planes of carbon atoms due to delocalized electrons.
Molecular Crystals
- Molecular crystals are formed by molecules held together by van der Waals forces and/or hydrogen bonding.
- These forces are weaker than ionic or covalent bonds.
- Examples include benzene, ammonia, and carbon dioxide (dry ice).
- These crystals have relatively low melting points and are generally soft.
Metallic Crystals
- Metallic crystals consist of atoms of the same metal held together by metallic bonds.
- Metallic structures are body-centered cubic (BCC), face-centered cubic (FCC), or hexagonal close-packed (HCP).
- The bonding electrons are delocalized, contributing to the high electrical conductivity of metals.
- They have varying degrees of hardness and melting points.
Amorphous Solids
- Amorphous solids lack a regular, repeating three-dimensional atomic arrangement.
- Glass is one example.
- Glasses are formed by mixing molten substances that do not crystallize upon cooling.
- The composition of glass, often SiO2, along with other oxides gives different properties and uses (e.g., pure quartz, Pyrex, soda-lime glass).
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