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Psych 251 > Chem 225 > Flashcards

Chem 225 Flashcards

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1
Q

symmetry elements/operations

A

Describe specific symmetry relationships between areas within an object.
Examples: rotation axis, plane of symmetry

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2
Q

point group

A

A collection of symmetry elements that describes the overall symmetry of an object. All point groups include the identity element E.
Examples: C2v, C2h , Td, Oh

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3
Q

irreducible representations

A

A set of characters within a Character Table describing a mathematically allowed sub-symmetry of the point group.
Examples: within C2v, 1, -1, 1, -1

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4
Q

characters

A

Positive or negative values within an irreducible representation (within a Character Table), referring to symmetric, antisymmetric, or asymmetric with respect to a symmetry element.
Examples: 0, 1, -1, 2, -2, 3, -3

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5
Q

Identity element, E

A

Present in all point groups with a positive character of 1, 2 or 3. The identity operation does not move the object (molecule), and is present for mathematical reasons

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6
Q

Rotation axis, Cn

A

Symmetry with respect to a partial rotation around a central axis that passes through the object. n is an integer that defines the ‘fold’ of the
rotation, which is the number of turns to complete 360°, i.e. 2 (180° each), 3 (120° each), 4 (90° each), 5 (72° each), 6 (60° each), etc.
- For objects with more than one axis of symmetry that are perpendicular, the axis with the highest fold is referred to as the principal axis.

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7
Q

Plane of symmetry, σ

A

symmetry with respect to a plane through the center of the object. A plane that includes the principal axis is labelled σv and a plane that is perpendicular to the principal axis is
σh.

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8
Q

Center of inversion, i

A

symmetry with respect to a combination of a C2 and σh. Inversion of all components of the molecule through the center of the molecule

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9
Q

Improper axis, Sn

A

Symmetry with respect to a combination of a fraction of a rotation Cn (n is greater than 2) and reflection through a perpendicular plane.
Example in red is S 4, 90° rotation about
the C 2 and reflection through the
perpendicular plane.

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10
Q

cubic close packing (ccp)

A
  • ABCABC
  • packing of hexagonal 2D layers
  • also known as face centered cubic
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11
Q

hexagonal close packing (hcp)

A
  • ABAB
  • packing of hexagonal 2D layers
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12
Q

non close-packed arrays

A
  • Simple cubic lattice and body-centered cubic
  • These are the simplest lattices
  • Both are built from square 2D packed
    layers
  • They differ only by whether alternate layers are placed in “holes” or directly over the previous layer’s
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13
Q

Effect of temperature of metals and semiconductors

A
  • Semiconductors: the temperature dependence of the number of mobile electrons is more important
    than the temperature dependence on lattice vibrations. As a result the resistivity of decreases with increasing temperature
  • Metals: the temperature dependence of resistivity is determined by the lattice vibrations. As a result the resistivity increases with increasing temperature
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14
Q

1:1 structures

A
  • Rock salt (NaCl) structure: fcc (ccp) lattice for both Na+ and Cl-. Many other salts have the same structure, need a 1 to 1 stoichiometry
  • Cesium chloride: simple cubic lattice, salts containing large cations. Octahedral holes in close-packed anion structure only have room for cations 41% of anion size. So this adopts a non-close packed structure
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15
Q

1:2 structures

A
  • Fluorite (CaF2): a face-centered cubic lattice of Ca2+ ions with F- in all tetrahedral holes
  • Zinc blended: Only half the tetrahedral holes filled. Preferred coordination number of 4
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16
Q

Oxidation vs. reduction

A

Oxidation: Loss of electrons of the reducing agent
Reduction: Gain of electrons of the oxidizing agent

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17
Q

Galvanic cells vs. electrolytic cells

A
  • In electrolytic cells, the passage of electrical current causes a chemical reaction to occur whereas in a Galvanic (or Voltaic) cell, a spontaneous chemical reaction causes electrons to flow
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18
Q

Hydrogen compounds

A
  • ionic hydrides (E+H-): True ‘saline’ (ionic) hydrides only form with groups 1 and 2
  • covalent hydrides
    -hydridic: H slightly - , polymeric solids, electron bridging, BeH2, B2H6, MgH2, SiH4, SnH4, etc
    • neutral: CH4, PH3, AsH3
    • protic: H slightly + , high Bp gases or liquids, NH3, H2O,H2S, HX
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19
Q

Uses of hydrogen

A
  • Fuel cells, energy storage
  • Chemical synthesis (e.g. addition to double bonds w/ catalyst)
  • Reduction of salts to metals instead of C ( e.g. MoO3 + 2H2 → Mo + 3H2O )
  • Used in synthesis of ammonia by the Haber-Bosh process
20
Q

Group 1: Alkali metals

A
  • Silvery, low melting metals by electrolysis of molten salts
  • Form mostly soluble salts that are powerful reductants and very reactive as a result
  • Dissolved in liquid NH3 to form ‘solvated electron’ solutions
21
Q

Flame tests for group 1 metals

A
  • Atomic emission spectra
  • Li: crimson, Na: yellow, K: purple, Rb: red-violet, cesium: blue
22
Q

Group 1 uses

A
  • Lithium ion batteries: Rechargeable, High energy density, Used in portable electronics, flammable (e.g. LiC6, lithium graphite)
  • LiC6: INTERCALATION COMPOUND
  • Organolithium reagents: C-C bond formation (similar to, but more reactive than, Grignard reagents, RMgX)
    • M-C bond formation
    • Anionic polymerization initiator (e.g. styrene to polystyrene)
23
Q

Group 2: Alkaline earth metals

A
  • Silvery metals, higher mp than group 1, less reactive bc harder to oxidize due to increasing Zeff.
  • reactivity with water: M= Mg &laquo_space;Ca, Sr< Ba
24
Q

Group 2 uses

A
  • MgO: A REFRACTORY MATERIAL= Very high mp, insulator, not ‘workable’
    • Ceramics, or oven/furnace liners
  • Calcium: limestone (CaCO3) is ‘calcined’ with heat to make lime/quick lime CaO, with water it becomes ‘slaked’ lime Ca(OH)2
  • Calcium carbide (CaC2): formed from carbon and CaO at high temperatures, hydrolysis releases acetylene gas. Used in miners lamps
25
Q

Group 13: metals and non-metals

A

exemplifies almost all periodic trends:
- change from covalent (B) to ionic bonding (Al down) = Decreasing Q/r ratio
- nonmetal (B) and metal behaviour (Al down) = Decreasing Q/r, more orbitals
- diagonal relationships (B →Si and Be →Al) = Similar Q/r: increased charge
offsets increasing size

26
Q

inert pair effect

A

s-electrons have electron density near the nucleus and the very high Z means electrons experience an increase in mass if close to the nucleus - a relativistic effect. This lowers the s-electron energy enough that it takes too
much energy to remove them, i.e. they become ‘inert’
Ex: Oxidation states: +3 for most but heaviest member Tl dominated by +1.

27
Q

Where and how aluminum metal

A
  • Most abdundant metal in Earth’s crust
  • Huge energy cost to mine
  • Prepared by electrolysis (Hall-Héroult Process)
  • Al2O3 (Na3AlF6 ) + 2C (s) → 2 Al (l) + CO (g) + CO2 (g)
28
Q

Aluminum hydroxides and oxides

A
  • Dissolves in acids or bases: amphoteric
  • Conversion of hydroxides to oxides is condensation (- H2O)
  • Al2O3 and B2O3 is like quartz
  • SiO2 (silica) and borosilicates are similar to pyrex
29
Q

Boranes and boric acid

A
  • Boranes: B/H compunds
  • Types: Arachno (Web, B4), Nido (Nest B5) and Closo (cage, B6 or C2B4)
  • Boric acid: B(OH)3, weak acid (pKa 9.5), extensive hydrogen bonding in a sheet structure, used as a mild antiseptic: eye/mouth wash
30
Q

Group 14

A
  • group includes non-metals (C), semi-metals (Si, Ge) and metals (Sn, Pb)
  • all elements catenate to some degree
  • inert pair effect for Sn and especially Pb (2+ state is important)
31
Q

Allotropes of carbon

A
  • Graphite (sp2): conductor
    • Very soft: layers can slide over one another. Intercalation compounds: e.g. C6K
  • Diamond (sp3): insulator
    • Extremely hard, must break several bonds to move C atoms
  • Graphenes (sp2):
  • Fullerenes
  • Nanotubes
32
Q

Silicones/siloxanes uses

A
  • Produced on a massive scale
    industrially
  • Low toxicity and cheap leads
    to many uses:
  • Oil baths, hydraulic fluids (stable to many chemicals and high T)
  • Personal care products as lubricants: shampoo, conditioner, antiperspirant, hair gels, toothpaste, shaving cream
  • Greases, sealants, gaskets
  • Medical implants
33
Q

Group 15: pnictogens

A
  • non-metals except for Bi
  • tend to catenate
  • multiple bonding rapidly declines down the group:
  • N≡N bond strength (942 kJ/mol) is >50% stronger than 3 times the N-N bond strength (600 kJ/mol)
  • P≡P bond strength (480 kJ/mol) is 30% less than 3 times the P-P single bond energy (630 kJ/mol)
34
Q

Arsenic compounds

A
  • Bind strongly to S and disrupts S-S bonds
  • Poisonous: Napoleon was poisoned with As – deliberately or not!
  • Strong antibacterial properties
  • Ehrlich’s Magic Bullet: Developed the cure for Syphilis. Originator of chemotherapy
35
Q

Group 15 pesticides and nerve agents

A
  • Pesticides: Parathion, diazinon, malathion (the safest)
  • Nerve agents: Sarin and soman
    • Mechanism: Acetylcholine esterase (ACE) inhibitors – interfere with the ‘off’ switch leading to uncontrolled nerve impulses and death
36
Q

Group 16: chalcogenides

A
  • Oxygen: O2 or O3 gases, insulator, pπ-pπ bonding, very little catenation, strong oxidizing ability
  • Sulfur: S8 and many other Sn, insulator, bonding mainly with O, extensive catenation, weak oxidizing ability
  • Selenium: Sen helical chains, semiconductor, no multiple bonding, significant catenation, no oxidizing ability
    Tellurium: Ten helical chains, semiconductor, no multiple bonding, significant catenation, no oxidizing ability
37
Q

Group 16 catenation

A
  • Sulphur has the 2nd greatest tendency to catenate after carbon
  • S8: yellow sulfur, S chain: red liquid, cooled: black plastic sulfur
  • But…many other catenation compounds of S, Se, and Te are known
  • MoS2 (lubricant) and FeS2 (Fool’s gold) contain S2 2- anions
38
Q

Group 16: selenium and tellurium

A
  • Se and Te are photosensitive semiconductors: they conduct when exposed to light
  • The Xerox process: old printing method using a selenium-coated drum and charge
39
Q

Sulfur oxides

A
  • Combustion of any S-containing material (especially coal) produces SO2 (g)
  • SO2 slowly converts to SO3 which dissolves in water to form H2SO 4 (part of acid rain):
    • degrades limestone used in buildings
    • limits ability of freshwater to support fish/plants
  • But, SO2 can be useful:
    • Used in bleaching of wood pulp in pulp+paper industry
    • Antibacterial sprayed on fruit or added to wine as a preservative: dissolves in
      water and converts to sulphite (SO32-) salts
40
Q

Group 17: halogens

A
  • Fluorine: only -1 valence in compounds, weak F-F bond (extreme lone pair repulsion), reacts with virtually all elements (except N and O), extremely oxidizing, Eº = +2.87V, very strong and unreactive C-F bonds, e.g. teflon
  • Chlorine: yellow gas, Eº = +1.36V, PVC, other polymers, bleach (ClO -), solvents
  • Bromine: red liquid, Eº = +1.09V, Photographic film, flame retardants
  • Iodine: purple solid, Eº = +0,54V, disinfectant, X-ray contrast agent, catalysts
41
Q

Stereoisomers and types

A
  • Stereoisomers: same chemical formula, same bonds but different relative orientation of those bonds
  • Enantiomers: Mirror image, same physical
  • Diatereomers: Non mirror images, different physical properties (ex: cis vs trans or mer vs. fac)
42
Q

Strucral isomers and types

A
  • Structrual isomers: same formula, different atom connectivity
    1. Ionization isomers: interchange of an anionic ligand in 1st coordination sphere with anion outside the coordination sphere
    2. Hydration isomers: interchange another ligand in 1st coordination sphere with outer sphere water
    3. Coordination isomers: interchange of ligands in first coordination spheres of salt where both cation and anion are coordination complexes
    4. Linkage isomers: same ligand bonded to the metal in different ways (an ambidentate ligand)
43
Q

π donors vs. π acceptors

A
  • π donors: ligand with filled π orbitals, greater M character in anti-bonding, greater L character in bonding, weak field, smaller delta o
  • π acceptors: ligand with empty π orbitals, greater L character in anti-bonding, greater M character in bonding, strong field, larger delta o
44
Q

Generalizations about delta o

A

1) For a given M n+ ion, the position of L in the spectrochemical series predicts the magnitude of delta o
2) For a given ML6 with M in different oxidation states: the higher oxidation state has the higher delta o
3) For a given MLn in a single triad: heavier metal has the higher delta o
4) BUT, there is NO TREND in delta o across the series for different M with the same ox. state and ligand set

45
Q

Types of radio active decay

A
  • Beta (β) radiation involves emission of high-speed electrons. Neutron converts to proton + ejected e-
  • Gamma (γ) radiation involves emission of a very short wavelength (high energy) photon. It usually accompanies other radioactive decay because it represents the energy lost when the nucleus changes into a more stable arrangement
  • Positron emission involves an anti-electron being generated. Proton converts to neutron + ejected positron
  • When a positron encounters an electron, they annihilate each other and produce two gamma rays
  • Electron capture involves a nucleus capturing an orbital electron. Electron is captured and combines with a
    proton to give a neutron
46
Q

N and Z ratios in stability belt

A
  • Z ≥ 84 decay by alpha emission (decreases both N and Z)
  • High N/Z ratio nuclides usually decay by beta-emission (Nˇ, Zˆ)
  • Low N/Z ratio nuclides usually decay positron emission or electron capture (Nˆ, Zˇ)

Psych 251 (6 decks)

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