Group 16

Question 1

Why is O-O weaker than S-S?

Answer 1

Because of repulsion between lone pairs on small O atoms

Question 2

Why is O=O stronger than S=S?

Answer 2

Because pi overlap of 2p orbital in O is better and hence forms a stronger bond requiring more energy to break

Question 3

What’s the structure of elemental sulfur?

Answer 3

Single-bonded S8 rings

Question 4

Why does group 16 have high 1st IP in general?

Answer 4

Because of their relatively high electronegativity, hence high IP

Question 5

What two forms of Se exist?

Answer 5

Hexagonal (grey pellets)

Amorphous (red powder)

Question 6

What’s the importance of Se?

Answer 6

It’s an essential nutrient - 55µ per day

However its toxic in higher doses

Question 7

What is Te used in?

Answer 7

Metallurgy - study of chemical materials properties and behaviour

Semiconductors - solar panels

Question 8

Why is ozone pale blue when liquid?

Answer 8

Due to lone pairs

Question 9

Why is ozone an irritant in lower atmosphere?

Answer 9

It’s a component of photochemical smog

Question 10

What does ozone do?

Answer 10

It absorbs UV radiation in the upper atmosphere

Question 11

Why are CFCs damaging to the atmosphere?

Answer 11

Because they destroy several thousand ozone molecules through radical mechanisms

Question 12

What are the properties of ozone?

Answer 12

Highly oxidising

∆fH˚ = +285 KJ / mol

Very endothermic

Question 13

What are oxides of most electro±ve elements?

Answer 13

Oxides of most electro-ve elements are acidic

Oxides of most electro+ve elements are basic

Question 14

What’s the bond angle of SO2?

Answer 14

119.5˚ - exists in resonance

S(lV) - combustion in air

Question 15

How is SO3 produced?

Answer 15

2SO2 + O2 —> SO3

V2O5 catalyst - contact process

Question 16

What the structure of SO3 in gas and solid states?

Answer 16

120˚ - trigonal planar, exists in resonance in gas phase

Forms cyclic trimer in solid state

Question 17

Is SO3 Lewis acidic or basic?

Answer 17

Very Lewis acidic - sulfur atom is very electron deficient

Question 18

Why is H2SO3 not as acidic as H2SO4?

Answer 18

Because H2SO3 only has 1 S=O unit whereas H2SO4 has 2 S=O units, making it more acidic

Question 19

How are 2 moles of H2SO4 formed from SO3?

Answer 19

(Conc H2SO4). H2O
SO3———> H2S2O7 ——> 2H2SO4

Oleum is formed initially - very viscous

It is them diluted/hydrated to form 2 moles of sulfuric acid

Question 20

How does acid rain?

Answer 20

Acid rain forms when atmospheric SO2 dissolves in rainwater

Question 21

What’re the uses of thiosulfate?

Answer 21

Can be reacted with acid to form a sulfur precipitate - reduces Cl in pool water

Question 22

What is characteristic about tetrathionate’s structure?

Answer 22

A strong S—S bound which bridges the molecule

Question 23

What’s special about the oxidation states of thiosulfate?

Answer 23

Question 24

Why does water have such exothermic enthalpy of formation and such high BP compared to H2S and H2Se?

Answer 24

The very exothermic (favourable) enthalpy of formation of water is due to strong O-H bonds

It’s high BP is due to H-bonding

Question 25

Why is water’s bond angle so different to H2S and H2Se?

Answer 25

H2O bond angle of 104.5˚is due to sp3 hybridised orbitals

H2S and H2Se show no s-p hybridisation, s orbitals with respect to p orbitals

Question 26

Why is hydrogen peroxides BP higher than water?

Answer 26

Because it has 2 O atoms both with 2 lone pairs each

Hence forms more hydrogen bonds

Question 27

Why is H2O2 so unstable?

Answer 27

Because the O-O single bond is very unfavourable, the O=O double bond drives the reaction

This makes the enthalpy change of reaction of the decomposition of hydrogen peroxide very favourable / exothermic.

Question 28

What are the domestic uses of hydrogen peroxide?

Answer 28

Within sodium percarbonate is H2O2 held within crystal lattice

Light sticks