U3 SLOA

exceptions to the octet rule

1. group 2 and 13 elements

2. expanded octet in elements with an empty d sublevel

properties of covalent bonds

1. low reactivity

2. stable

give 3 examples of dative bonds

NH4+, H3O+, CO

when do delocalised electrons happen?

1. Bonding e are in a double bond

2. There is more than one possible position for a double bond in a molecule or polyatomic ion

The ___ of a small covalent molecule is determined by the ___ of its ___ 

The shape of a small covalent molecule is determined by the position of its nuclei 

accroding to VSEPR, what effect do ED repulsion have.

minimising the energy of the molecule by maximising the distance in betwee atoms.

explain why PCl3 can also be PCl5 (expanded octet)

3 rules for determining preferred structure from formal charge

4 Characteristics of ideal gas at all temperature and pressures 

1. Gas particles occupy negligible volume (because particles are small and move quickly, it is very low density) 

2. Particles are in constant, random motion, but in straight lines and random directions. 

3. Particle collisions are elastic, so no energy is lost. 

4. No force of attraction between particles 

Characteristics of real gas 

• Similar to ideal gas in high temperature and low pressure 

• At low temperature: particles move more slowly, more significant force of attraction 

• At high pressure: higher density of particles --> volume of gas particles and force of attraction are more significant 

3 properties of radicals

1. High enthalpy

2. Very reactive

3. Short lifetime

give 3 examples of radicals

Cl, Br, H, NO, OH, O2-, C6H6

wavelength of light that breaks intermediate between single and double (ozone)

<330 nm

wavelength of light that breaks double bonds (oxygen gas)

<240nm

reaction mechanims of ozone formation

reaction mechanims of ozone depletion

reaction mechanims of ozone depletion with CFCs

describe the ozone equilibirum in the stratosphere

• In the stratosphere, ozone is produced and broken down steadily 

• The ozone layer blocks a range of UV, protecting the Earth 

• But air pollutants disrupt this equilibrium  

• Chlorofluocarbons (CFCs) from human activities act as catalysts in the depletion of ozone. So that ozone depletion > ozone formation 

compare and contrast stratosphere ozone versus trophosphere ozone

Stratosphere  High altitude  Contains 90% of atmospheric ozone  Acts as a primary UV shield  Issue  Long term global warming trend  Antarctica ozone hole

Troposphere  Lower altitude  Contains 10% of atmospheric ozone  Toxi effects on humans and vegetation  Issue  Episodes of high surface ozone in urban and rural areas

demonstrate monosubstituion and disubstitution with C2H6 with Cl2

why are alkanes low reactivity

• High bond enthalpy for C-C and C-H (needs a strong source of energy, such as a combustion reaction, or a with a very reactive substance) 

• Non-polar nature of the bonds and molecules (lack of polar region --> low reactivity with common reactants) 

what special conditions are required to overcome alkane’s low reactivity

1. The formation of reactive free radical intermediate

2. Use high energy UV to form free radicals

Free radical substituion mechanism

Outline initiation in free radical substituion mechanism

• Photolytic fission

• UV light photodissociates CL2 into radicals

Outline propagation in free radical substituion mechanism

• A series of steps where free radicals are formed and used in later steps

• Chlorine radical is reformed/ regenerated, setting up a chain reaction/ reaction cycle to continue propagation

Outline termination in free radical substituion mechanism

• 2 free radicals combine

• Removes free radicals, stops the reaction

• Larger alkanes may be produced as a result