chart with bonding energy; repulsive energy on top, attractive energy on bottom; lowest bonding energy is where the bond will occur in nature
High bonding energy = high E (o)
closer atoms will be to each other, shorter the bond length will be, stronger the bond
ex: solids, hard, high melting temperatures, low thermal expansion coefficient
small r (distance between atoms)
repulsive force is dominating
large r (distance between atoms)
attractive force is dominating
Why is it important to know where energy is minimum?
Everything in nature goes towards minimum energy
tendency to acquire electrons
strong, determined by valence electrons (main bonds you know)
TRANSFER of valence electrons; metal + nonmetal; Large difference in electronegativity required; occurs between + and - ions
LARGE bond energy *NON-DIRECTIONAL*
atoms achieve noble gas configuration by SHARING VALENCE ELECTRONS; involves hybridization (mixing of orbitals) *DIRECTIONAL*
valence electrons are being shared among all atoms in material; free electron gas= electron and thermal conductivity *NON-DIRECTIONAL*
Which bonds are directional and which are nondirectional?
Ionic and Metallic= non-directional Covalent= directional
involve all electrons, not just valence; WEAK
induced dipolar interactions due to fluctuations in electron cloud, ACTIVE FOR ALL MOLECULES/ATOMS
if covalent bonds form between atoms of distinct electronegativity, permanent dipole moments occur (depending on symmetry of molecules) ex: water (H2O)-> responsible for higher boiling point of water as compared to methane
corresponds to number of protons in nucleus for natural elements
nuclei with same atomic number "Z" but different number of neutrons
atomic mass unit
Atomic mass unit (amu)
a unit of mass used to express atomic and molecular weights; = (1/12)*mass of C-12
= 6.02 x 10^23 (1/mol)
Schrodinger's wave-mechanical model of atoms
wave particle duality of electrons
Qn; characterize the electronic structure of atoms; nlms
primary/principle quantum number (n)
corresponds with primary energy level (Bohr energy level) n = 1, 2, 3... n = k, l, m...
secondary quantum number (l)
describes the shape of subshells (orbitals) that exist in the primary energy level l = (n-1) l = 0, 1, 2, 3 l = s, p, d, f
tertiary (magnetic) quantum numbers (m)
describes the number of orbitals and their orientation within a subshell m= -l to +l (...-2, -1, 0, 1, 2...)
electron spin quantum number (s)
describes the determination of an atom's ability to generate a magnetic field or not; s= +(1/2) or -(1/2)
describes the distribution of electrons among the available states
no two electrons can can agree in all four quantum numbers
four components of the disciplines of material science engineering?
processing can change structure, properties depend on structure
Structure of a material is based off...?
how it was processed
function of a material's properties tells us its...?
investigation of the relationship between structures and properties of materials
designing/engineering of material structures to meet certain property requirements (material selection/processing)
moderate melting temperature moderate bond energy moderate coefficient of thermal expansion **METALLIC BONDS**
high melting temperature LARGE BONDING ENERGY small coefficient of thermal expansion **IONIC & COVALENT BONDS**
**Directional Properties ***Secondary bonding dominates*** small melting temperature small bond energy large coefficient of thermal expansion **COVALENT & SECONDARY BONDS**
regular, periodic arrangement of atoms
crystalline solids represent atoms/ions as...?
represents atoms/ions as "hard spheres"
Unit Cell (UC)
smallest repeat unit that allows to reproduce the positions of all atoms by translating UC integer multiples along its edges; chosen to represent the symmetry of the LATTICE
a discrete but infinite regular arrangement of points (lattice sites) in a vector space