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ENCN221 Exam Questions & Answers 2024/2025 R199,08
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ENCN221 Exam Questions & Answers 2024/2025
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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...

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  • August 20, 2024
  • 28
  • 2024/2025
  • Exam (elaborations)
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  • encn221 exam questions answers

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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 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

, non-crystalline materials - ANSWERSno periodic packing

occurs for complex structures, rapid cooling



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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