Group 16

Question 1

Describe variation in metallic character down the group and across the periods in p-block

Answer 1

1. Increasing non-metallic behaviour across the period

2. Increase non-metal to metalloid to metal down a group

Question 2

What is the maximum oxidation state in group 16

Answer 2

1. +6

2. Doesn’t exist for O

Question 3

What oxidation states are available for oxygen

Answer 3

1. -2, -1, 0

Question 4

What are the two common allotropes of oxygen

Answer 4

1. O2 and O3

Question 5

Describe O2

Answer 5

1. Paramagnetic- unpaired electrons in its electronic ground state
2. Forms a pale blue liquid and solid at low temperatures

Question 6

Describe how O2 is synthesised industrially

Answer 6

1. Fractional distillation of liquid air

Question 7

Describe how O2 is synthesised in the lab

Answer 7

1. Electrolysis of water or decomposition of either potassium chlorate or hydrogen peroxide
2. KClO3 –> 2KCl + 3O2
3. 2H2O2 –> 2H2O + O2

Question 8

Describe bonding in ozone

Answer 8

1. Pale blue gas at room temp
2. Bond length in between single bond of hydrogen peroxide and double bond of O2
3. The pi-bonding is involving a p-orbital on O with 2e- in it and 1e in p-orbital on each end O
4. 2e in bonding MO which is stretched across 2 bonds so pi bond order is 0.5
5. Overall bond order (single + pi-bond) = 1.5

Question 9

What are physical properties of oxygen

Answer 9

1. Strong oxidising agent

3. O3 is stronger than O2

Question 10

Why is S-S stronger than O-O

Answer 10

1. Lone pairs of e- that repel each other and weakens O-O single bond
2. O is smaller than S so have stronger repulsions and therefore weaker bonds

Question 11

Describe general trend in bond strength down the group

Answer 11

1. Atom size increases as we go down a group, so atom-atom contact increases
2. As atom size increases so does the size of the orbitals and as atoms increase in size the distance between them increases and bond strength decreases
3. As we go down groups bond energy decreases

Question 12

Why does S have more allotropic forms than any other element

Answer 12

1. Large number of rings that can be formed with S-S bonds and the many ways it can pack in the solid state
2. Preference for formation of single bonds as stronger than multiple

Question 13

What happens when S8 is heated

Answer 13

1. Heat to 119 degrees- melts –> yellow liquid, becomes less viscous
2. Continue to 159 degrees –> Viscosity increases dramatically, now s8 rings open to form S8 chains, these interact to form S16, S24 etc
3. Heat further- viscosity decreases again, cleave apart long chains to form smaller units

Question 14

Why is there difference in behaviour between O and S

Answer 14

1. Bond strengths
2. O pi-bond is more than twice the strength of the single bond
3. Formation of O=O is favoured compared to 2*O-O and the opposite is true for S

Question 15

What happens to the energy difference between s and p orbitals as you go down the group

Answer 15

1. Increases

2. Less s-p mixing and bonds become more p-like character

Question 16

As you go down the group what happens to the hydrides

Answer 16

1. The H-M-H angles get closer to 90 degrees

2. Les sp2 type more p orbital

Question 17

What happens to the boiling point of group 16 hydrides down the group

Answer 17

1. Decrease from O - hydrogen bond

2. Then increase - Van der Waals increasingly polarisable as we go down the group

Question 18

Describe acidity from group 15-17

Answer 18

1. NH3 is most basic
2. Acidity increases from left to right along with increasing electronegativity
3. Acidity also increases down the groups as bonds get weaker so reduce stability and increase acidity

Question 19

Describe water

Answer 19

1. Solid has lower density than liquid due to opening up of H-bonding
2. Ice floats on water
3. At least 9 distinct forms

Question 20

Describe H2O2

Answer 20

1. v pale blue liquid
2. Liquid at rt, more dense and viscous than H2O
3. OS= -1
4. Can be both a strong oxidising and reducing agent

Question 21

Show disproportionation of H2O2

Answer 21

1. H2O2 –> H2O + 1/2 O2
2. Metal and glass catalysed
3. Stored in plastic containers

Question 22

What is the only halide of oxygen

Answer 22

1. Fluoride

Question 23

Describe different oxygen halides

Answer 23

1. OF2- colourless gas, v toxic, radical decomp to F2 and O2
2. OFH- colourless liquid, v toxic, decomp to HF and O2 at RT
3. O2F2- prepared by passing electrical discharge through F2 and O2, solid which decomposes at RT over days

Question 24

Describe bonding in O2F2

Answer 24

1. Bonding of fluorine to the O2 molecule is by overlap of the 2p on fluorine with pi* on O2
2. Fluorine is unique in being more electronegative than oxygen, so there is little increase in pi* electron density thus preserving the double bond of O2.

Question 25

Describe how SF6 can be formed

Answer 25

1. F is oxidising enough to allow S to get to OS of 6- thermodynamically unstable but kinetically stable
2. The stability is a result of 6 F atoms surrounding the S and stopping attack at delta+ centre
3. Favourable as F-F bond in unfavourable so negative enthalpy of formation
4. Cl-Cl bond is favourable so SCl6 is less stable

Question 26

Describe SF4

Answer 26

1. 10 Valence electrons but an still use as lewis acid
2. Readily hydrolysed
3. Properties as both lewis acid and base
4. See-saw structure

Question 27

Describe S2F2

Answer 27

1. Analogue of O2F2

2. Two isomers

Question 28

Describe sulfur oxides

Answer 28

1. S=O bonding even though multiple bonding is a feature of the top row elements
2. sigma and pi bond components are comparable in sulfur oxide bonds so s=o can be made

Question 29

What are important oxides of sulfur

Answer 29

1. SO2- gas- Cyclic trimer based on S3O3 ring in solid state

2. SO3

Question 30

Describe SeO2

Answer 30

1. Chain in solid state

2. SeO2 molecules in gas phase