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CHEE380 > Atomic and Molecular Structure > Flashcards

Atomic and Molecular Structure Flashcards

1
Q

Metallic bonding

A

Atomic orbitals combine to form delocalized electron cloud shared by large number of atoms - non-directional

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2
Q

Secondary bonds

A
  • Van der Waals: weak bonding induced by fluctuating/permanent molecular dipoles
  • H bonding: bonding between protons + available electron pair
  • Directional
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3
Q

Is covalent bonding directional?

A

Yuh

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4
Q

Is ionic bonding directional?

A

No

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5
Q

Comparison of bond energies for diff bonds

A
  • Ionic: large
  • Covalent: variable
  • Metallic: variable
  • Secondary: smallest
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6
Q

Melting temperature bond energy relationship

A

Tm larger if Eo larger - proportional to depth of potential energy curve

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7
Q

Elastic modulus bond energy relationship

A

E is larger if Eo larger - proportional to curvature at ro (unstretched length) energy

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8
Q

Coefficient of thermal expansion bond energy relationship

A

Coeff is larger if Eo is smaller - proportional to symmetry at ro energy (low Eo = asymmetry)

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9
Q

Hardness bond energy relationship

A

Proportional to Eo - hardness is resistance of surface to plastic deformation + influenced by height of total force curve so materials w/high Tm are harder

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10
Q

Electrical conductivity from bond nature

A
  • Ionic + covalent are poor conductors as electrons not free to leave atoms used in bonding
  • Metallic are good as low ionization energy + electrons free within crystal lattice
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11
Q

Ceramics material properties (they have ionic + covalent bonds)

A

Large bond energy, large Tm, large E + small coeff

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12
Q

Metals material properties (metallic bonding)

A

Variable bond energy, moderate Tm, moderate E + moderate coeff

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13
Q

Polymers material properties (covalent + secondary)

A

Directional properties, secondary bonding dominates, small T, small E + large coeff

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14
Q

How does band splitting work?

A
  • Occurs 1st on outer shells - effect smaller as we go towards nucleus + splitting of given level increases as distance decreases
  • Discrete energy states w/small energy differences (continuum)
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15
Q

Valence band

A

Band having highest energy electrons at 0K

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16
Q

Conduction band

A

Next band at energy > valence band

17
Q

Fermi energy

A

At 0K all electrons have energy smaller or equal to Ef

18
Q

Conductors

A

Energy needed very small to move in conduction region + become free electrons

19
Q

Insulators

A

Large energy band gap exists between full valence band + conduction region

20
Q

Semi-conductors

A

Same as insulators but w/small band gap

21
Q

What is resistance of pure metals near 0 temperature?

A

Very small

22
Q

Does resistivity increase or decrease with temperature?

A

Increase

23
Q

Does resistivity increase at absolute 0 temperature?

A

Yuh

24
Q

Are good conductors pure or impure?

A

Pure

25
Q

What are bad conductors typically?

A

Alloys

26
Q

Do metals deformed by work hardening have higher or lower resistivity than same metal in stabilized state?

A

Higher

27
Q

Fermi energy

A

Energy where probability of occupancy is 50% for any T>0K

28
Q

Is electron mobility higher or lower than hole mobility?

A

Higher - more difficult to move a hole than an electron

29
Q

n-type extrinsic semiconductor

A

Surplus of 1 electron for each P atom added - electron easily goes to conduction band and delta E needed is very small

30
Q

p-type extrinsic semiconductor

A

Missing 1 electron for each B atom added creates hole - hole easily goes in conduction in valence band and delta E needed very small

31
Q

Do n or p types have higher fermi levels?

A

n

32
Q

Diode

A

p-n rectifier junction (current only flows in 1 direction)

33
Q

Transistor

A

Has 3 semiconductor sections - current only flows between source + drain if potential is applied at base

34
Q

Applications of transistor

A
  • Amplifier: signal sent to base is amplified between emitter + collector
  • Electronic switches: current only flows between collector + emitter when voltage applied at base
35
Q

Microfabrication

A

Series of methods developed for fabrication of well defined structures on micro + nano scale - main app is integrated circuits

36
Q

Photolithography

A

Makes patterns on microscale - uses UV light to transfer a pattern in a metal mask to a photo reactive material (photoresist polymer) on a surface

37
Q

Peltier effect

A

If you force a current through a bi-metal junction then when electrons go from A to B they gain energy at interface so energy taken from material … cooling effect + vice versa

38
Q

Peltier effect for p type n type semiconductors

A

Electrons flowing from p type semiconductor to n type results in energy transfer/ cooling depending on circuit

CHEE380 (6 decks)

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