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Question 1

sigma bonds

Answer 1

• head-on/ end-to-end overlap of atomic orbitals
• s-s orbitals, p-p orbitals and s-p orbitals.
• ## single bonds basically

Question 2

Pi bonds

Answer 2

• formed from the sideway overlap of adjacent p-orbitals
• lie above and below the sigma bonds

Question 3

double bond

Answer 3

one sigma
+
one pi bond

Question 4

triple bond

Answer 4

one sigma bond
+
two pi bond

Question 5

exceptions to the octet rule

Answer 5

H
Li
Be
B
Al

Question 6

expansions of the octet rules

Answer 6

• elements in period 3 and above have the posibilities to have more than 8 electrons
• bc there is d-subshell present
• ‘expansion of the octet’
• PCl5, SF4, ClF3, I3-, SF6, BrF5, XeF4

Question 7

molecular geometry

Answer 7

shape of the molecules based on the relative orientation of the atoms

Question 8

domain geometry

Answer 8

relative orientation of all the bonding and lone pairs of electrons

Question 9

electron and molecular geometry when there is 5 bonded electron pairs, and 0 lone pair

Answer 9

domain geometry: trigonal bipyramidal
molecular geometry: trigonal bipyramidal

Question 10

electron and molecular geometry when there is 4 bonded electron pairs, and 1 lone pair

Answer 10

domain geometry: trigonal bipyramidal
molecular geometry: see saw

Question 11

electron and molecular geometry when there is 3 bonded electron pairs, and 2 lone pair

Answer 11

domain geometry: trigonal bipyramidal
molecular geometry: T-shaped

Question 12

electron and molecular geometry when there is 2 bonded electron pairs, and 3 lone pair

Answer 12

domain geometry: trigonal bipyramidal
molecular geometry: linear

Question 13

electron and molecular geometry when there is 6 bonded electron pairs, and 0 lone pair

Answer 13

domain geometry: octahedral
molecular geometry: octahedral

Question 14

electron and molecular geometry when there is 5 bonded electron pairs, and 1 lone pair

Answer 14

domain geometry: octahedral
molecular geometry: square based pyramid

Question 15

electron and molecular geometry when there is 4 bonded electron pairs, and 2 lone pair

Answer 15

domain geometry: octahedral
molecular geometry: square planar

Question 16

Formal Charge

Answer 16

the charge assigned to an atom in a molecule, assuming that all the electrons in the bonds are shared equally between atoms, regardless of differences in electronegativity
FC= (number of valence electrons) - ½(number of bonding electrons) - (number of non-bonding electrons)
or
FC= V - ½B - N

Question 17

What does FC tell you about the Lewis structures

Answer 17

The Lewis structure which is preferred is the one which:
- the difference in FC of the atoms is closest to zero
- has negative charges located on the most electronegative atoms

Question 18

bond order

Answer 18

fractional bond in resonance structures
bond order = total number of boning pair / total number of positions

Question 19

Ozone

Answer 19

• resonance structure
• central O atom has 3 electron domains and a lone pair
• domain geometry - triangular planar
• molecular geometry - bent linear
• 117 bond angle
• ## bond order = 1.5

Question 20

Catalytic Depletion of Ozone

Answer 20

The bonding and structure of ozone is key to understanding how the catalytic depletion of ozone occurs in the stratosphere
High energy UV radiation in the stratosphere breaks the oxygen-oxygen double bond creating oxygen atoms
O2 (g) → O⋅ (g) + O⋅ (g) ∆H +ve, UV light, λ < 242 nm

These oxygen atoms have unpaired electrons - they are known as free radicals
The free radicals are highly reactive and quickly attack oxygen molecules forming ozone in an exothermic reaction, which raises the temperature of the stratosphere
OZONE FORMATION O⋅ (g) + O2 (g) → O3 (g) ∆H – ve

Ozone requires less energy to break than oxygen
It produces an oxygen molecule and an oxygen free radical:
OZONE DEPLETION O3 (g) → O⋅ (g) + O2 (g) ∆H +ve, UV light, λ< 330 nm

The radical reacts with another ozone molecule making two molecules of oxygen in an exothermic reaction
OZONE DEPLETION O3 (g) + O⋅ (g) → 2O2 (g) ∆H – ve

The temperature in the stratosphere is maintained by the balance of ozone formation and ozone depletion in a process known as the Chapman Cycle
It is not a closed system as matter and energy flow in and out, but it is what is called a steady state
The Chapman cycle, downloadable IB Chemistry revision notes

The Chapman cycle

Catalytic Depletion
The two main man made culprits that accelerate the depletion of ozone are nitrogen oxides and CFCs
Nitrogen monoxide, NO, is produced from the high temperatures inside internal combustion engines
If you count the valence electrons in nitrogen monoxide (5 + 6 =11), the odd number tells you it is a free radical as it has an unpaired electron
The nitrogen monoxide reacts with ozone forming oxygen and a nitrogen dioxide radical
NO⋅ (g) + O3 (g) → NO2⋅ (g) + O2 (g)

The nitrogen dioxide produced is also a free radical (it has 5 + 6 + 6= 17 electrons) and you can show the second step where it reacts with another molecule of ozone, producing oxygen and regenerating the NO⋅ radical:
NO2⋅ (g) + O3 (g) → NO⋅ (g) + 2O2 (g)

An alternative to the second step shows the NO2⋅ reacting with an oxygen radical to produce the same products but in a different stoichiometry
NO2⋅ (g) + O⋅ (g) → NO⋅ (g) + O2 (g)

The nitrogen monoxide is regenerated so it has a catalytic role in the process
Combining the two equations and cancelling out the NO⋅ and NO2⋅ and you arrive at the overall depletion of ozone
O3 (g) + O⋅ (g) → 2O2 (g)

A similar process happens with CFCs
The C-Cl bond in the CFCs is weaker than the C-F bond and breaks more easily in the presence of UV light creating chlorine radicals
CCl2F2 (g) + UV → CClF2⋅ (g) + Cl⋅ (g)

The chlorine radicals attack ozone and are regenerated at the end of the cycle
Cl⋅ (g) + O3 (g) → ClO⋅ (g) + O2 (g)

ClO⋅ (g) + O⋅ (g) → Cl⋅ (g) + O2 (g)

Once again a molecule of ozone has been destroyed by a catalytic free radical
The net effect of these reactions is that these pollutants have created an imbalance in the natural ozone cycle leading to an overall depletion in stratospheric ozone
CFCs are greatly damaging to stratospheric ozone and have been largely replaced by safer alternatives following the 1985 Montreal Protocol
The depletion of ozone has allowed greater amounts of harmful UV light to reach the surface of the Earth
UV light has been linked to greater incidence of skin cancer and cataracts as well as the destruction of phytoplankton and reduced plant growth

Question 21

Hybridization

Answer 21

occurs when different atomic orbitals mix to form new orbitals for bonding

Question 22

sp3

Answer 22

• tetrahedral
• 109.5
• 2s and three 2p orbitals blend

Question 23

sp2

Answer 23

• planar triangular
• 120
• 2s and 2p orbitals

Question 24

sp

Answer 24

• linear
• 180
• 2s and 1p orbitals