Lecture 1: Atomic Bonding and Crystal Structure Flashcards
What is the seperation of 2 atoms denoted as?
r
what is the bond between two atoms like?
a spring
What is another name for interaction energy of 2 atoms?
potential energy
What is the equation for interaction/potential energy?
where r is the lattice separation and m and n are some constants
A is attractive interaction strength and B is repulsive interaction strength
With attraction-repulsion, when dU/dr = 0 at r=r0, what is happening?
U (potential energy) is at a minimum
r0 is the equilibrium separation
What happens if
1. r<r0
2. r = r0
3. r> r0
- repulsive force
- zero force
- attractive force
What are general and specific examples of metallic bonds?
metals and alloys
Ag, Cu, Fe, FeCr
What are general and specific examples of ionic bonds?
oxides, chlorides
ZrO2, NiO, NaCl,
What are general and specific examples of covalent bonds?
some ceramics, semiconductors
SiC, Si, diamond
What are general and specific examples of van der waals bonds?
polymers, inert gases
Xe, Ar
Describe metallic bonds
valence electrons “delocalize” from an atomic core, become “free” electrons shared by all atoms. these “free” electrons from “electron gas” or “sea of electrons”
What bonds do metals and alloys typically have? examples?
metallic bonds
Na, Cu, Fe, NiFe
What do metallic bonds look like visualized?
In what kind of material can electrons drift in?
metals with high mobility
What is the electrical conductivity, thermal conductivity, and ductility like for metallic bonds?
High electrical conductivity
High thermal conductivity (heat is conducted by electrons)
Good ductility
What happens in ionic bonding?
valence electrons “transfer” from metallic atoms to non-metallic atoms, form cations (+) and anions (-) so electrons are not mobile
what does a visualization of ionic bonding look like?
What are two examples of oxide ceramics
MgO, ZrO2
Is an anion’s or cation’s ionic radius larger?
anion is larger than
Describe the bond strength (implications), electrical conductivity, and thermal conductivity of ionic bonds?
ionic bonds are typically strong, which means high melting point (ex MgO Tm>2800)
low electrical conductivity (insulators)
low thermal conductivity (heat is transferred by phonons – lattice vibration– bc no free electrons)
Describe covalent bonds?
valence electrons are shared between neighboring atoms so each atom can have a stable electronic configuration
what does a visualization of covalent bonds look like?
What can carbon form? bonds?
graphite and diamond structures (both with covalent bonds)
What can covalent bonds form? 4 examples
ceramics, semiconductors or insulations
SiC, Si, diamond, graphite
Describe the bond strength, electrical conductivity, and thermal conductivity or covalent bonds?
typically strong bonds with high melting points
low electrical conductivity
high thermal conductivity (by phonons), which is different than ionic bonds
Describe Van der Walls (VDW) bonds?
adjacent atoms or groups of atoms act as electric dipoles
give examples of VDW bonds (general and specific)
inert gasses, interaction between polymer molecules
Ar, Kr, Xe
What is the bond strength and electrical and thermal conductivities of VDW bonds?
VDW bond very weak – low melting point
low electrical and thermal conductivites
In general, how do melting point and bond energy/strength relate?
Melting point increases with bond strength/energy
What kind of bond is Fe
metallic
List the seven crystal systems are there? list them.
cubic, tetrag, ortho, monoclinic, triclinic, hexagonal, rhombohedral
What do the crystal systems look like?
What is it called when a material’s properties depend on crystal direction?
anisotropic
How do you calculate the miller indices? what is their notation in variables?
intercepts –> reciprocals
hkl
What is the notation for a specific plane vs. family of equivalent planes?
use a bar for a neg sign**
What is the notation for a vector in a specific direction vs. family of equivalent directions?
