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Inorganic Chemistry > Group 16,17,18 > Flashcards

Group 16,17,18 Flashcards

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1
Q

use of polonium

A

chemical weapons (highly radioactive)

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2
Q

astatine

A

highly radioactive

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3
Q

helium

A

2nd most abundant element - used in NMR (super conducting magnet)

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4
Q

group 16 - general properties

A

= chalcogens

-same periodic trend as in group 13-15
-non-metals = O,S
-semi-conductors = Se, Te
-others = metallic
last group to contain true metal = polonium

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5
Q

what is catenation?

A

ability to form chains

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6
Q

which elements is catenation important for?

A

S, Se + Te

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7
Q

group 16 - oxidation states

A

max. = +6 (important for S)

max. for oxygen = +2

most common = -2,-1,0

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8
Q

allotropes of oxygen

A

O2 and O3

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9
Q

ozone

A

strong oxidising agent

-each O has 6 valence e-
-central O = sp2 hybridised
-1 l.p. in sp2 orbital
-1 l.p. in p orbital
-each terminal O involved in 1 bond (1 unpaired e- in each)
-total of 4e- in p orbitals

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10
Q

what do electrode potentials show?

A

how effective an oxidising agent something is

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11
Q

ozone - bond lengths

A

shorter than O-O in H2O2 but longer than O=O in O2

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12
Q

allotropes of S

A

S has more allotropic forms than any other compound + has more compounds with single bonds

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13
Q

trend in allotropes down group

A

decreased tendency to form multiple bonds

decreased tendency to catenate (related to bond energies)

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14
Q

trend in acidity down group

A

bonds get weaker down group (poorer overlap + increased mismatched)

reduced stability

increased acidity

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15
Q

trend in sp mixing down group

A

energy difference between s+p orbitals increases

less s-p mixing

bonds become more p-like in character
H-M-H gets closer to 90°

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16
Q

hydrogen peroxide

A

v. pale blue liquid

liquid at rtp

more dense and viscous than water

oxn state = -1

can be both a strong oxidising agent (acidic conditions) + reducing agent (basic conditions)
prone to disproportionation - promoted by storing in glass

17
Q

halides of oxygen

A

only consider fluorides
highly reactive

[O2F2]
-similar structure to H2O2
-prepared by passing electrical discharge through F2 and O2
-solid
-decomposes at rtp over days
-extremely powerful oxidative fluorinating agent (hard to control)

NpF4 + O2F2 -> NpF6 + O2

18
Q

sulfur halides

A

S2F2 - v. unstable and highly reactive

SF4 - acts as both lewis acid and lewis base

[why?]

6e- from sulfur and 4e- from fluorine (10e- altogether - hypervalent)

expect to act as Lewis acid

10e- to 12e- = expansion of octet

F is oxidising enough to allow S to get group oxidation state to +6

should be reactive to H2O but due to high kinetic stability, H2O can’t get past 6 S-F bonds to react

high activation barrier to overcome despite favourable reaction thermodynamically

SF6 -> SF4/SF2
F-F = weak compared to Cl-Cl
no strong driving force for decomposition

19
Q

basic oxides

A

involves metal oxides

react with acids to produce salt + H2O

20
Q

acidic oxides

A

involves non-metals

reacts with acids to produce salt + H2O

21
Q

amphoteric oxides

A

reacts with both acids and bases to produce salt + H2O

formed by metalloids and some metals that lie at border of metal/non-metal behaviour

22
Q

neutral oxides

A

react with neither acid or base

23
Q

important oxides of S + properties

A

SO2 + SO3

high Zeff
elements = smaller
behave like elements in the first row

24
Q

why do we have O2 and S8?

A

O2 = 2 p-orbitals

S8 = 3 p-orbitals (more diffuse ∴ weaker π component - more favourable to have σ-bonds)

O=O - strong π component - x2 2p overlap; higher electron density; not v. diffuse

S=S - weak π component - x3 2p overlap; v. diffuse

SO2 - 2p+3p overlap; 3p contracted due to high Zeff of S; allows π-bonding to occur

25
Q

preparation of sulfur oxides

A

S + O2 -> SO2 (burn in air)

2SO2 + O2 -> 2SO3 (use of catalyst)

26
Q

what type of oxides are SO2 + SO3?

A

[acidic]

SO2 -> H2SO3
SO3 -> H2SO4

27
Q

sulfuric acid

A

prepared by Contact process

4FeS2 + 11O2 -> 8SO2 + 2Fe2O3

SO2 purified

2SO2 + O2 + catalyst -> 2Fe2O3
2SO3 dissolved in conc. H2SO4 to give oleum (H2SO4 . SO3)

28
Q

SO3 reactivity with water

A

doesn’t react - too violent; no solution (mist instead)

29
Q

F2

A

pale yellow gas

v. corrosive

most reactive element known

30
Q

unique properties of F

A

strongest oxidising agent

ΔHe- attachment out of order - smaller; most electron repulsion

weak F-F bond - kinetically reactive
hydride complexes show unusual H-bonding effects

31
Q

trend in pKa down halogen group

A

decrease down group - acidity increases as bond strength decreases

expect HF to be most acidic as it’s most electronegative but it’s not

[reasons]

  1. HF bond has partial ionic character (charges slightly separated)
  2. [H3O+.F-] = ion pair
    stick together due to strength of H bonding
    don’t generate lots of H3O+ - decreases acidity
  3. F- + HF ⇌ [HF2]-
    lower conc. of HF present in initial solution
32
Q

fluorine - trend in boiling point

A

high - due to H bonding (less than water)

[reasons]

  1. H-F has unidirection H-bonding
  2. H bonding retained in gas phase - heat to 60°C + still have some H bonding
33
Q

interhalogen compounds

A

4 families - XY, YX3, XY5, XY7

prep = direct combination of elements

highly reactive (ΔG < 0 - exergonic)

X-F = more stable than X-Cl

IF = most stable (due to polar contribution)
charged interhalogens also known

F always -1 oxidation state

biggest atom = central

stabilisation required non-coordinating (weakly basic) anions

34
Q

halogen oxides

A

can form acidic species

increased number of 0, acid becomes stronger

oxidation state becomes more +ve

oxygen stabilises conjugate base

35
Q

group 18

A

= noble gases

all monoatomic gases

helium = 2nd most abundant element in the universe - demand > supply

36
Q

unique property of helium

A

when cooled to 2.2K, transforms to He(II) = superfluid (has 0 viscosity)

37
Q

is the I.E. of the noble gases expected to be high or low?

A

high - due to stable octet, highest possible Zeff

Inorganic Chemistry (15 decks)

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