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Chemistry Of The Elements > p block (G16-18) > Flashcards

p block (G16-18) Flashcards

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1
Q

how does metallic character change down G16 and why?

A

metallic character increases due to the decrease in ionization energy

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2
Q

under what circumstance does oxygen have a positive oxidation state?

A

when it bonded to a more electronegative element (eg. Flourine)

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3
Q

why does O2 not oxidise and what can be done to overcome it?

A

high kinetic energy barrier which can be overcome by increasing the temperature

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4
Q

why must 2 molecules of O2 be required to see the pale blue oxygen in liquid form

A

so that there is no overall change in spin

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5
Q

what are the 2 allotropes of oxygen

A

ozone and dioxygen

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6
Q

what are the 2 ways of forming ozone?

A
  1. electrical charge from thunderstorms
  2. UV radiation

both react with O2 to form O radical which reacts with another O2 to form ozone

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7
Q

what is the function of ozone

A
  1. absorbs UV region to protect the planet’s surface
  2. used in water purification (as it is more reactive/better oxidizing agent)
  3. forms part of urban smog
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8
Q

what are the allotropes of sulphur and which one is the most stable

A

S5-S12 rings and S8 is most stable

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9
Q

which element in G16 is the best at catenation and why?

A

sulphur because everything beyond that is too big thus poorer overlap and oxygen has the most LPLP repulsion as it is the closest together

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10
Q

what are the 2 states of selenium and tellurium

A

Se: silver grey metal (helical polymeric chains), red powder
Te: silvery white crystalline and amorphous black powder

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11
Q

Why does the oxidation state increase going down G16

A

except for oxygen, all other elements can promote their electrons into low lying d orbitals (2x p -> d) and (1x s -> p)

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12
Q

2 reasons for oxygen forming more oxides than nitrogen

A
  1. oxygen is more electronegative
  2. O2 has lower bond dissociation energy than N2
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13
Q

what are the 2 ways of forming water?

A
  1. Direct reaction of its elements
  2. Electrolysis
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14
Q

Why do the heavier elements form hydrides that are 90 degrees rather than bent (105-109)

A

More p character (orthogonal) than s character so not fully sp3 hybridized

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15
Q

How to the boiling points of G16 hydrides change down the group

A

Water has hydrogen bonding, then from H2S it increases as VdW interactions increases

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16
Q

what is the difference between boiling point and thermal stability

A

boiling point: intermolecular interactions
thermal stability: intramolecular interactions (bond strengths)

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17
Q

how does thermal stability change down G16 and why?

A

decreases down the group due to poorer orbital overlap

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18
Q

how does acidity change down G16 and why?

A

increases down the group as poorer overlap means that the hydrogen is more readily deprotonated (donated)

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19
Q

what is the most inert sulphur halide and why?

A

SF6:
1. all of sulphurs available orbitals are used for bonding
2. steric protection due to octahedral geometry (difficult to access central atom)
3. S-F are in the same period thus orbital overlap is very strong (strong bonds)
4. greater ionic contribution (as F is very electronegative)

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20
Q

why is SF4 so reactive?

A

open face is easy to attack (due to its structure) -> see saw

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21
Q

what is the structure of sulphites and sulphates and which one is more reactive

A

sulphite: SO3 with 1 double bond + lone pair (more reactive)
sulphate: SO4 with 2 double bonds

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22
Q

how is SO2, SO3 and their corresponding oxoions (SO3- and SO4-) produced?

A

CaSO4 + C to make CaO CO and SO2

under a vanadium oxide SO2 becomes dynamic equilibrium with SO3

oxoanions can be formed by reacting the oxides with water in acidic conditions

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23
Q

when would flourine have a 0 oxidation state?

A

in its elemental form (diatomic)

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24
Q

what do the G17 elements exist as

A

dimers (diatomic elements X-X)

25
Q

what is the boiling point trend down group G17

A

BP increases due to increased VdW interactions

26
Q

Describe the trend of bond energy down G17

A

Decreases due to poorer orbital overlap but flourine is the smallest atom on group 17 thus have the most LPLP repulsions (even more than N and O)

27
Q

What can be used to explain the colours of the elements in G17

A

MO theory: transition of electrons from the HOMO to the LUMO (energy difference determines colour)

28
Q

How does the HOMO and LUMO gap change down G17?

A

HOMO LUMO gap decreases thus higher wavelengths (lower energy) of light is absorbed

29
Q

How is flourine and chlorine produced? what are its uses

A

F: extracted from ores such as CaF2 with an acid (eg. H2SO4) and becomes HF
use: UF6 for nuclear reactors and SF6 as inert atmosphere for insulated windows

Cl: electrolysis of NaCl
use: bleach, making polymers

30
Q

Why are chloro compounds in decline?

A

Carcinogenic and depletes the ozone layer

31
Q

How do the thermal stability and bond strengths of hydrogen halides change down G17

A

Weaker due to poorer orbital overlap and H-F having a much higher boiling point due to H bonding

32
Q

How is the acidity/basicity of hydrogen halides?

A

All are acid in water (proton donor)

33
Q

Why is HF a particularly weak acid? 2 reasons

A
  1. HF bonds are very strong
  2. Deprotonating would mean breaking the hydrogen bonding which is energetically unfavorable
34
Q

How can the acidity of HF be improved?

A

excess HF for the anion (F-) to form stable HF2- (3c 2e bonding)

35
Q

What are oxo acids?

A

compound with an oxygen bound to an acidic proton (can dissociate)

36
Q

Why is flourine have weak VdW interactions?

A

Small and highly charged makes F polarizing but not very polarizable (thus lower boiling point and does not form a lot of interactions with other things)

37
Q

Which is more reactive: perchlorate or chlorate ion and why? what are their uses?

A

Chlorate (ClO3-) is more reactive than
perchlorate (ClO4-) because of the exposed lone pair

chlorate use: bleach, matches, fireworks
perchlorate use: solid fuel rockets

38
Q

Which of the G17 elements cannot be the central atom and why?

A

F because it is too small (only a substituent)

39
Q

Under what conditions can the central atom take on more flourines ?

A

Elevated temperatures and pressures

40
Q

Why can Xe form compounds with F and O

A

The high bond energy/ionic character of Xe-F and Xe-O compensates for the large ionization energy of Xe

41
Q

Why is Xe with more substituents more reactive than with less?

A

XeF6 is the most reactive because the greater no. of electronegative elements means that more electron density is being widthdrawn from the central atom (Xe) thus making it more electron deficient and more reactive/willing to accept electrons

42
Q

How are Xenon oxides formed?

A

hydrolysis of xenon hexaflourides (addition of water) -> forms Xe=O which is more stable

43
Q

What are isoelectronic molecules?

A

Species that contain the same number of valence electrons thus also isostructural

44
Q

what are the similarities between lithium and magnesium?

A

metallic radius
boiling point
forms organometallic compounds
forms ionic nitrides

45
Q

what are the similarities between boron and aluminium?

A

forms dimers due to high electronegativity (prefers sp3 over sp2)

46
Q

what are the similarities between boron and silicon?

A

semi-metallic
unreactive
high melting point
strong bonds to oxygen
in their halide form they both behave as lewis acids (proton acceptors)
-> can react with water to form E(OH)3 and displace the halide group

47
Q

what are the 2 ways that oxygen is produced?

A

electrolysis of water
fractional distillation of liquid air

48
Q

why are 2 oxygen molecules needed in the liquid oxygen reaction?

A

spin selection rules (no overall change in spin)

-1 + 1 = 0 for triple oxygen

spins are total 0 for singlet oxygen

49
Q

how is sulphur produced?

A

natively through volcano deposits and hot springs + present in minerals

50
Q

why does oxygen prefer forming a double bond for catenation rather than single bond?

A

in a single bond the lone pairs are too close together causing LP LP repulsions which is less stable (oxygen molecules are small)

in a double bond in lone pairs are oriented away from each other which is more stable

51
Q

what are the uses of some of the G16 elements?

A

oxygen: fuel, air purification
sulphur: H2SO4
selenium: photoelectric cells
tellurium: additive to low carbon steels

52
Q

what is the reaction from hydrogen peroxide to water and oxygen called?
what can hydrogen peroxide be used for?

A

disproportionation

(the oxygen is simultaneously oxidised and reduced from the same species)

used in water treatment and bleach

53
Q

what is a use of iodine?

A

found in table salt to avoid iodine deficiency

iodine-131 is used as cancer treatment

54
Q

what is the naming used for oxo-anions?

A

hypochlorous acid (1O)

chlorous acid (1O + =O)

chloric acid (1O + =O x2)

perchloric acid (1O + =O x3)

acidity increases due to the stability of its conjugate base (due to pi donation/delocalisation)

55
Q

why is molecular flourine/ covalent flourides volatile?

A

since flourine is very unpolarizable, it has extremely weak vdw thus has a low mp/bp making it volatile (subject to evaporation)

56
Q

what are some of the uses of G18 elements?

A

He: light, non-flammable gas
-> research balloons, grocery scanners
-> in liquid form can be used for magnets in NMR/MRI scanners

Ne, Kr, Xe -> neon signs

Ar -> inert atmosphere for synthesis

Ra -> radioactive species that is soluble in lipids

57
Q

what is the difference between borazine and benzene?

A

benzene only undergoes substitutions and the electrons and delocalised equally throughout the entire structure

borazine has a dipole moment within the molecule due to the different electronegativity values of B and N

58
Q

describe the differences between graphite and boron nitride

A
  1. boron nitride is chemically inert and forms eclipsed layers (B above N) rather than staggered layers like in graphite
  2. due the difference in polarity between boron and nitrogen the intermolecular forces of attraction between the layers are strong (unlike in graphite which are weak) which makes them more difficult to cleave and slide over each other
  3. the electrons are localised between the covalent bond of B and N rather than being delocalised like graphite thus boron nitride is an electrical insulator while graphite is an electrical conductor

Chemistry Of The Elements (7 decks)

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