ENCN221 Exam Questions & Answers 2024/2025
properties valence electrons determine - ANSWERSchemical electrical thermal optical, and contribute to bonding in solids
electronegativity - ANSWERSthe ability of an atom to gain or lose an electron
behaviour of repulsive and attractive forces w...
properties valence electrons determine - ANSWERSchemical electrical thermal optical, and contribute to
bonding in solids
electronegativity - ANSWERSthe ability of an atom to gain or lose an electron
behaviour of repulsive and attractive forces with distance - ANSWERSattraction increases with distance,
repulsion also increases. repulsion increases and decreases more quickly so there is a point where the
forces balance
what is elastic modulus related to (subatomically) - ANSWERShow the attractive and repulsive forces
behave- is the graph steep or shallow
how is melting temp related to bond energy - ANSWERSproportional
how is bond energy related to bond strength - ANSWERSproportional
how is coefficient of thermal expansion related to bond energy - ANSWERSinversely proportional
high and low electronegativity results in which bond - ANSWERSionic
low and low electronegativity results in which bond - ANSWERSmetallic
high and high electronegativity results in what bond - ANSWERScovalent
what are the properties of a metallic vs a covalent vs ionic bond - ANSWERSall strong. metallic
ductile/malleable/conductive
,van der Waals forces - ANSWERSa slight attraction that develops between the oppositely charged regions
of nearby molecules
fluctuating dipole - ANSWERSIntermittent, uneven distribution of electrons around the atom or molecule
forming a weak bond around the atoms/molecules
permanent dipole - ANSWERSA small charge difference across a bond resulting from a difference in
electronegativities of the bonded atoms.
bonding of ceramics - ANSWERSionoic and covalent- large bond energy
large Tm
large E
small alpha (coef of thermal expansion)
bonding properties of metals - ANSWERSvariable bond energy
moderate Tm
moderate E
moderate alpha
bonding properties of polymers - ANSWERSsecondary bonding- directional properties
small Tm
small E
large alpha
amorphous - ANSWERSnon crystalline
Crystalline Materials - ANSWERS- atoms pack in periodic, 3D arrays
- typical of : metals, many ceramics, some polymers
unit cell - ANSWERSthe smallest group of particles within a crystal that retains the geometric shape of
the crystal
lattice points - ANSWERSthe vertices of a unit cell
lattice parameters - ANSWERSThe lengths of the unit-cell edges.
basis - ANSWERSmolecule located on lattice points
why are metals dense - ANSWERSmetallic bonding is non directional so it can pack in the most efficient
way
all atomic radii are the same
BCC - ANSWERSbody-centred cubic. 9 atoms per cell. each corner and centre of lattice
FCC - ANSWERSface centred cubic. 14 atoms per cell. each corner and centre of each face
HCP - ANSWERShexagonal close pack. 17 atoms. each corner, centre top and bottom face, centre plane
(3)
number of equivalent atoms for each structure - ANSWERSBCC 2
FCC 4
HCP 6
Atomic Packing Factor - ANSWERSAPF. the volume of atoms in a selected unit cell divided by the volume
of the unit cell
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