MATLS 2A04 Video Notes Review: Atomic Structure, Bonding, and Crystallography

Question-and-answer flashcards covering interatomic bonding, potential energy relationships, lattice concepts, symmetry elements, crystal systems, and unit-cell properties based on the provided notes.

What is the interatomic distance?

The distance between the nuclei of two atoms (denoted r).

What is the equilibrium bond length?

The bond length where interatomic forces balance (often denoted ro).

What is bond energy?

The energy required to break a bond (denoted EN).

Name the main types of bonding mentioned.

Ionic bonding, Covalent bonding, Metallic bonding, van der Waals bonding, and Hydrogen bonding.

What factors determine interatomic forces between atoms?

Forces vary with interatomic distance and balance at equilibrium; the magnitude and type of force depend on distance.

What information does a potential energy curve provide near the equilibrium bond length?

Equilibrium bond length ro, equilibrium bond energy Eu, and the curvature near ro related to stiffness or elastic modulus of the bond.

How does the curvature near ro relate to elastic properties?

Larger curvature around ro leads to a greater elastic modulus (stiffness) of the bond.

What does a deep and narrow trough in the potential energy curve indicate in the notes?

Low thermal coefficients.

How is bond energy related to melting point?

Larger bond energies typically correspond to higher melting points.

What is meant by bond directionality in the notes?

Ionic and covalent bonds are typically directional, whereas metallic bonding is non-directional.

What is hydrogen bonding?

A type of bonding involving hydrogen that is generally weaker than ionic/covalent bonds but important in many systems.

Define lattice.

Discrete points in a lattice that form the periodic framework of a crystal.

Define unit cell.

The basic structural repeating unit of a lattice; the building block of the lattice.

Define primitive cell.

A unit cell that contains exactly one lattice point.

Do all lattices have translational symmetry?

Yes; all crystals possess translational symmetry.

Do lattice points always coincide with atom positions?

No; lattice points do not always coincide with atom positions.

What must a unit cell be able to do to reproduce the lattice?

It must be repeatable to produce the entire lattice.

What is meant by the corners of the unit cell having identical surroundings?

Due to translational symmetry, the environments at the corners are equivalent.

In 2D, do atom positions need to coincide with lattice positions?

No; atom positions do not need to coincide with lattice points in 2D arrangements.

List the 3D crystal systems mentioned.

Cubic, Tetragonal, Orthorhombic, Rhombohedral, Hexagonal, Monoclinic, Triclinic.

What are lattice parameters?

Axial lengths a, b, c and interaxial angles α, β, γ that describe the unit cell.

What are symmetry elements?

Translational, Rotational, and Reflection symmetry (and related concepts like center of symmetry and inversion).

What is translational symmetry?

A structure that maps onto itself by a translation vector; the smallest independent vectors are the unit cell vectors.

What is rotational symmetry?

An arrangement can be rotated about an axis by an n-fold rotation (e.g., 3-fold, 4-fold) and map onto itself.

What is center of symmetry (inversion center)?

A point where inversion through that point yields an identical arrangement.

What is reflection symmetry?

Mirror reflection across a plane; important alongside translation symmetry in crystals.

What is APF and what does it stand for?

APF stands for Atomic Packing Factor; it is the fraction of the unit cell volume occupied by atoms.

What is a coordination number?

The number of nearest-neighbor atoms surrounding a given atom.

How many atoms are in a simple cubic unit cell and what is its coordination number?

1 atom per cell; coordination number is 6.

How many atoms are in a body-centered cubic (BCC) unit cell and what is its coordination number?

2 atoms per cell; coordination number is 8.

What is meant by a close-packed structure in crystals?

A structure with maximum efficient packing, typically FCC or HCP, often described by ABAB or ABCABC stacking sequences.

What factors influence the density of a crystalline solid?

Density depends on the number of atoms per unit cell, the atomic masses, and the cell volume.