MATS105 Lecture 2 - Bonding in Materials
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Questions and Answers

What is the most fundamental physical unit that makes up materials?

Atoms

What are valence electrons?

The electrons in the outermost shell of an atom.

What are the primary bonding types?

Ionic, covalent, and metallic.

What is the charge of an electron?

<p>-1.602 x 10^-19 C</p> Signup and view all the answers

Which type of bonding is found in metals?

<p>Metallic bonding.</p> Signup and view all the answers

How are valence electrons involved in bonding?

<p>They are involved in the formation of chemical bonds, either by being shared (covalent bonding) or transferred (ionic bonding).</p> Signup and view all the answers

What is electronegativity?

<p>The tendency of an atom to attract electrons towards itself.</p> Signup and view all the answers

What is the range of electronegativity values?

<p>0.9 to 4.1</p> Signup and view all the answers

Compounds with a large difference in electronegativity are typically ionic.

<p>True</p> Signup and view all the answers

What type of bonding is found in ceramics?

<p>Ionic bonding.</p> Signup and view all the answers

What is the primary bond type found in metals?

<p>Metallic</p> Signup and view all the answers

Why is the term "close-packed" used to describe some metallic crystal structures?

<p>These structures have atoms arranged in a way that minimizes the amount of empty space.</p> Signup and view all the answers

What is the coordination number of a simple cubic structure?

<p>6</p> Signup and view all the answers

What is the atomic packing factor (APF) of a simple cubic structure?

<p>0.52</p> Signup and view all the answers

Which of the following elements has a simple cubic structure?

<p>Po</p> Signup and view all the answers

What is the coordination number of a body-centered cubic (BCC) structure?

<p>8</p> Signup and view all the answers

What is the APF of a BCC structure?

<p>0.68</p> Signup and view all the answers

Which of the following elements is not a BCC structure?

<p>Cu</p> Signup and view all the answers

How can you calculate the theoretical density of a material?

<p>By knowing the atomic mass, atomic radius, crystal structure, and Avogadro's number.</p> Signup and view all the answers

What is the difference between a single crystal and a polycrystal?

<p>A single crystal has a continuous and uniform crystal lattice throughout, while a polycrystal is made up of many small crystals with different orientations.</p> Signup and view all the answers

What is a grain in a polycrystalline material?

<p>A grain is a small, single crystal within a polycrystalline material.</p> Signup and view all the answers

Polycrystalline materials are typically anisotropic.

<p>False</p> Signup and view all the answers

What is the difference between allotropy and polymorphism?

<p>Allotropy is the ability of an element to exist in different crystal structures, while polymorphism is the ability of a compound to exist in different crystal structures.</p> Signup and view all the answers

What is the smallest repetitive volume that contains the complete lattice pattern of a crystal?

<p>Unit cell</p> Signup and view all the answers

How many crystal systems are there?

<p>7</p> Signup and view all the answers

How many Bravais lattices are there?

<p>14</p> Signup and view all the answers

What are Miller Indices?

<p>They are a set of three integers that describe the orientation of a crystallographic plane in a crystal lattice.</p> Signup and view all the answers

What is a crystallographic direction?

<p>A line that connects two lattice points in a crystal structure.</p> Signup and view all the answers

How do you determine the Miller Indices for a crystallographic plane?

<p>By taking the reciprocals of the intercepts of the plane with the crystal axes and then reducing them to the smallest integer values.</p> Signup and view all the answers

The mechanical properties of crystalline materials are always independent of the crystal structure.

<p>False</p> Signup and view all the answers

All engineering materials are polycrystals.

<p>False</p> Signup and view all the answers

Which of the following is an example of an anisotropic material?

<p>Single crystal</p> Signup and view all the answers

Polycrystals with randomly oriented grains are isotropic.

<p>True</p> Signup and view all the answers

Textured polycrystals are anisotropic.

<p>True</p> Signup and view all the answers

What is the main reason why the density of metals is generally higher than the density of ceramics?

<p>Metals tend to have a close-packed crystal structure, while ceramics have a less dense packing due to the size difference between metal and nonmetal ions.</p> Signup and view all the answers

The density of polymers is typically higher than the density of metals.

<p>False</p> Signup and view all the answers

What are some examples of polymorphic materials?

<p>Silica (SiO2) and zirconia (ZrO2)</p> Signup and view all the answers

What is the reason for the fracture of pure zirconia (ZrO2) when the temperature is lowered?

<p>The crystal structure of ZrO2 transitions from tetragonal to monoclinic, leading to volume expansion and causing stress-induced fracture.</p> Signup and view all the answers

Yttrium-stabilized zirconia (YSZ) is a type of ceramic that is commonly used for structural applications.

<p>False</p> Signup and view all the answers

What is the difference between noncrystalline materials and amorphous materials?

<p>There is no difference, both terms are synonymous and describe materials lacking a long-range order in their atomic arrangement.</p> Signup and view all the answers

Which of the following materials is typically noncrystalline?

<p>Glasses</p> Signup and view all the answers

The mechanical properties of noncrystalline materials are typically isotropic.

<p>True</p> Signup and view all the answers

Study Notes

Lecture 2 (W2) - Bonding in Materials

  • Lecture date: October 4, 2024
  • Lecturer: Maulik Patel
  • Email: [email protected]
  • Course: MATS105 Introduction to Engineering Materials

Topics Covered in the Module

  • Introduction to materials properties, microstructure, classifications, and selection
  • Materials: Metals and alloys, polymers and polymer-composites, structural ceramics and glasses, construction materials (cement, concrete, wood, etc.)
  • Mechanical properties/testing/failure of materials: Tensile test, deformation, hardness, fatigue, creep, impact fracture
  • Industrial alloys: Strengthening processes in metals, heat treatment of metals, industrial alloy specifications and application

Learning Objectives

  • How do atoms assemble into solid structures?
  • How does material density depend on its structure?
  • When do material properties vary with crystal orientation?
  • How are planes and directions in crystals named?
  • Callister Chapters 1 & 2

Atomic Structure

  • Electrons: Charge = -1.602 x 10⁻¹⁹ C, Mass = 9.11 x 10⁻³¹ kg
  • Nucleus: Protons and neutrons
    • Proton charge = 1.602 x 10⁻¹⁹ C, Mass = 1.67 x 10⁻²⁷ kg
    • Neutron: Neutral, Mass = 1.67 x 10⁻²⁷ kg
  • Atomic number (Z) = Number of protons = Number of electrons
  • Atomic mass number (A) = Z + N, where N = Number of neutrons
  • Isotopes: Atoms of an element with the same Z but different A

Electronic Configurations

  • Valence electrons: Electrons in the outermost unfilled shells
  • Filled shells are more stable
  • Valence electrons influence chemical properties and bonding
  • Example: C (atomic number 6) : 1s² 2s² 2p² (valence electrons = 4)

The Periodic Table

  • Columns have similar valence structures
  • Electropositive elements: Readily give up electrons to become positive ions
  • Electronegative elements: Readily acquire electrons to become negative ions
  • Electronegativity: Ranges from 0.9 to 4.1, Larger values indicate a tendency to gain electrons
  • Rule of Thumb: When difference in electronegativity (ΔX) > 1.7, compounds are usually ionic

Bonding Forces and Energies

  • Attractive forces (FA) and repulsive forces (FR) influence interatomic separation (r)
  • Net force (FN) = FA + FR
  • Repulsive energy (ER), Attractive energy (EA), and Net energy (EN) are plotted against interatomic separation, showing the equilibrium distance (r₀) and bond energy (E₀)

Ionic Bonding

  • Bond between metal and nonmetal

  • Metal donates electrons to nonmetal

  • Nonmetals accept donated electrons

  • Dissimilar electronegativities are required for ionic bonding

  • Example: MgO (Magnesium Oxide)

    • Mg: 1s² 2s² 2p⁶ 3s² → Mg²⁺: 1s² 2s² 2p⁶
    • O: 1s² 2s² 2p⁴ → O²⁻: 1s² 2s² 2p⁶

  • Ionic bonding occurs between oppositely charged ions due to Coulombic force

  • Strong, non-directional bonding

  • Range between 600 to 1500 kJ/mol

Covalent Bonding

  • Bond between atoms with similar electronegativity
  • Electrons are shared between atoms through overlapping orbitals (s and p)
  • Example: H₂ and CH₄
  • Relatively strong directional bonding

Metallic Bonding

  • Outer electrons released and shared among all atoms in a solid
  • "Sea of valence electrons" surrounds positively charged ions
  • Strong, non-directional
  • Atoms tend to be densely packed and metallic bonding is not directional. Nearest neighbors tend to be small to minimize bond energy.
  • Electron cloud shields cores

Primary Bonding in Most Materials

  • Metallic Bonding: Delocalized electron cloud
  • Ionic-Covalent Mixed Bonding: % ionic character = {1 - exp[-(0.25)(XA - XB)²]} × 100, where XA and XB are Pauling electronegativities

Bonding Types & Classification of Materials

  • Ionic: Large bond energy, non-directional (ceramics)
  • Covalent: Variable bond energy, directional (semiconductors, ceramics, polymer chains)
  • Metallic: Variable bond energy, non-directional (metals)
  • Secondary: Smallest bond energy, directional (inter-chain, inter-molecular)

Properties from Bonding: Melting Point

  • Melting point (Tm) is influenced by bond energy (E₀). Higher E₀ corresponds to higher Tm.

Properties from Bonding: Thermal Expansion

  • Thermal expansion coefficient (α) is influenced by bond strength. Stronger bonds have smaller α.

Atomic and Ionic Radii

  • Atomic radii decrease across a period and increase down a group (periodic table)
  • Ionic radii depend on charge. Cations are smaller and anions are larger than their corresponding neutral atoms.

Energy and Packing

  • Dense, ordered packing generally leads to lower energy in materials.

Classes of Materials

  • Classification by bonding types: Metals, Ceramics, Polymers
  • Classification by atomic order: Crystalline, Noncrystalline, Semicrystalline

Crystal Structures

  • Unit cell: Simplest repeating unit in a crystal
  • Lattice: Point arrangement that forms a crystal
  • Basis: Atoms or molecules associated with lattice points
  • 7 crystal systems and 14 Bravais lattices.

Theoretical Density

  • Density (ρ) = (Number of atoms/cell × Atomic mass) / [Volume of unit cell × Avogadro's number]

Allotropic or Polymorphic Transformations

  • Allotropy: Elements exist in multiple crystal structures
  • Polymorphism: Compounds exist in multiple crystal structures
  • Example: Zirconia (ZrO2) and Iron (Fe)

Single vs Polycrystalline Materials

  • Single crystals are anisotropic
  • Polycrystals are isotropic or anisotropic depending on grain orientation

Crystallographic Directions

  • Using a specified coordinate system, determine the direction vector and divide the components of the vector by their greatest common denominator. Enclose the components in square brackets(uvw)

Crystallographic Planes

  • Miller indices for a crystal are determined by taking the reciprocals of the intercepts of the plane with a, b, and c axes (the crystallographic axes). The common denominators are removed before enclosing them in rounded parentheses without commas (hkl).

Additional Notes

  • Various examples, diagrams (images, graphs) illustrate the concepts of bonding, crystal structures, and properties of materials.
  • Specific numerical data is given in tables about compounds, materials, and properties.

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MATS105 Introduction to Engineering Materials Lecture 2 (W2) Bonding in materials PDF

Description

Explore the fundamental aspects of bonding in materials in this quiz, based on Lecture 2 of MATS105. Understand concepts related to material properties, microstructure, and the different classifications of materials such as metals, polymers, and ceramics. Test your knowledge on mechanical properties and material behavior under various conditions.

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