Group 16 Flashcards
Why is O-O weaker than S-S?
Because of repulsion between lone pairs on small O atoms
Why is O=O stronger than S=S?
Because pi overlap of 2p orbital in O is better and hence forms a stronger bond requiring more energy to break
What’s the structure of elemental sulfur?
Single-bonded S8 rings
Why does group 16 have high 1st IP in general?
Because of their relatively high electronegativity, hence high IP
What two forms of Se exist?
Hexagonal (grey pellets)
Amorphous (red powder)
What’s the importance of Se?
It’s an essential nutrient - 55µ per day
However its toxic in higher doses
What is Te used in?
Metallurgy - study of chemical materials properties and behaviour
Semiconductors - solar panels
Why is ozone pale blue when liquid?
Due to lone pairs
Why is ozone an irritant in lower atmosphere?
It’s a component of photochemical smog
What does ozone do?
It absorbs UV radiation in the upper atmosphere
Why are CFCs damaging to the atmosphere?
Because they destroy several thousand ozone molecules through radical mechanisms
What are the properties of ozone?
Highly oxidising
∆fH˚ = +285 KJ / mol
Very endothermic
What are oxides of most electro±ve elements?
Oxides of most electro-ve elements are acidic
Oxides of most electro+ve elements are basic
What’s the bond angle of SO2?
119.5˚ - exists in resonance
S(lV) - combustion in air
How is SO3 produced?
2SO2 + O2 —> SO3
V2O5 catalyst - contact process
What the structure of SO3 in gas and solid states?
120˚ - trigonal planar, exists in resonance in gas phase
Forms cyclic trimer in solid state
Is SO3 Lewis acidic or basic?
Very Lewis acidic - sulfur atom is very electron deficient
Why is H2SO3 not as acidic as H2SO4?
Because H2SO3 only has 1 S=O unit whereas H2SO4 has 2 S=O units, making it more acidic
How are 2 moles of H2SO4 formed from SO3?
(Conc H2SO4). H2O
SO3———> H2S2O7 ——> 2H2SO4
Oleum is formed initially - very viscous
It is them diluted/hydrated to form 2 moles of sulfuric acid
How does acid rain?
Acid rain forms when atmospheric SO2 dissolves in rainwater
What’re the uses of thiosulfate?
Can be reacted with acid to form a sulfur precipitate - reduces Cl in pool water
What is characteristic about tetrathionate’s structure?
A strong S—S bound which bridges the molecule
What’s special about the oxidation states of thiosulfate?
Why does water have such exothermic enthalpy of formation and such high BP compared to H2S and H2Se?
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
Why is water’s bond angle so different to H2S and H2Se?
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
Why is hydrogen peroxides BP higher than water?
Because it has 2 O atoms both with 2 lone pairs each
Hence forms more hydrogen bonds
Why is H2O2 so unstable?
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.
What are the domestic uses of hydrogen peroxide?
Within sodium percarbonate is H2O2 held within crystal lattice
Light sticks
