The Ozone theory Flashcards
Name the four structures of the atmosphere
Troposphere
Stratosphere
Mesosphere
Thermosphere
Define electronegativity
The ability of an atom to attract the bonding pair of electrons in a covalent bond to itself.
Describe 100% ionic bonding
Complete transfer of electrons
Between metal and non metal
Very big differences in electronegativities
Describe 100% covalent bonding
Equal sharing of electrons
Non metals only
Identical electronegativities
Does electronegativity decrease or increase across a period and why?
It increases as number of protons in the nucleus increases. The number of shells stays the same so no change in shielding. The nucleus attracts bonding electrons more strongly.
Does electronegativity decrease or increase along a group and why
Number of shells of electrons increases so this increases shielding. Bonding electrons are further from the nucleus so there’s less attraction between the nucleus and these electrons despite the increased nuclear charge.
Explain covalent bonds with some ionic character
Happens as a result of uneven sharing of bonding electrons.
Occurs when the atoms involved have different electronegativities- the bigger the difference the more polar the covalent bond.
Are hydrocarbons polar or non-polar?
They are non-polar as the difference between Carbon and Hydrogen is very small.
Describe when you would and wouldn’t have a polar molecule
Polar molecule: Permanent overall dipole and individual dipoles do not cancel out.
Non-polar molecule: No overall dipole as its symmetrical the individual dipoles cancel out.
Which bonds are strong and weak?
Ionic, covalent and metallic are strong.
Intermolecular bonds are weak.
Describe instantaneous dipole- induced dipole bonds (IDID)
All molecules have them.
Electrons are constantly moving in molecule.
Uneven distribution of electrons = instantaneous dipole in one molecule.
This causes induced dipoles.
The attraction between two different dipoles is the ID-ID bond.
Describe the trend in boiling and melting point down bigger atoms and molecules groups
MP and BP increase.
More electrons.
More and stronger ID-ID bonds
More energy needed to separate molecules.
What does increased branching in molecule do to the BP and MP?
Decreased BP.
Decreased strength of ID-ID bonds as there is less contact between molecules.
What is permanent dipole- permanent dipole bond?
Attraction between molecules with a permanent dipole.
Stronger than ID-ID bonds.
Exist as well as ID-ID bonds.
Only occur in polar molecules.
What is permanent dipole- induced dipole?
Permanent dipole induces a temporary one in a species that is normally non-polar.
Describe Hydrogen bonds
Strong PD-PD bond.
Is the electrostatic attraction between a H+ and lone pair of electrons.
ONLY occurs when H is bonded to N/O/F.
Define activation enthalpy
The minimum amount of energy required by a pair of colliding particles for a reaction to occur.
Define rate of reaction
The change in concentration of reactants or products with time.
What happens in the concentration of a reactant increases
There are more particles in a given volume and the collision frequency increases.
Describe the effect of pressure on the collision theory
As pressure increases particles are closer together and there are more particles in a given volume. This increases the frequency of collisions.
Describe the effect of surface area on collision theory
Reducing the article size increases SA so more particles are exposed on the surface so there will be a greater frequency of collisions so increases the rate.
Describe the effect of temperature on the collision theory.
Particles have more energy so more collisions ( E> Ea )
Greater proportion of successful collisions. The particles move faster and collide more frequently.
Explain the effect of a catalyst on the collision theory
Provides an alternative route with a low activation energy. A greater proportion of collisions have energy larger than the new Ea. A greater proportion of particles have enough energy to react when they collide. So more successful collisions.
What is a homogenous catalyst and give an example.
Same physical state as reactants and an example is a chlorine radical in the destruction of Ozone. The chlorine radical is regenerated so reacts many times again as a catalyst.
What is a heterogenous catalyst and how does it work.
Reactant gas adsorbs onto the catalyst surface. The bonds in the reactant molecules are weakened lowering the activation energy so less energy is needed to break the reactant bonds. The reaction occurs and product bonds are formed. The product molecules desorb from the catalyst surface.
What is homolytic fission
Symmetrical covalent bond breaking. One electron from the bonding pair goes to each atom. The products have an unpaired electron so are radicals. Radicals are extremely reactive.
What is heterolytic fission
Unsymmetrical covalent bond breaking. Both electrons move to one atom in the bond. Positive and negative ions formed. The electrons move to the more electronegative element.
What are the physical properties of haloalkanes
Have a permanent dipole.
Not sufficiently polar to be soluble in water.
MP and BP dependent on the instantaneous- dipole induced- dipole rather than decreasing strength in permanent dipole- permanent dipole bonds.
How do you produce a haloalkane from alkenes.
Electrophilic addition.
Reagent: Hydrogen halide
Conditions: RTP
What is the amine group
NH2
How do you produce a haloalkane from alkanes
Free radical substitution
Reagents: Cl2 or Br2
Conditions: UV light
Describe the first stage of a free radical substitution reaction
Initiation:
Homolytic fission forms a halogen radical which are extremely reactive.
Describe the second stage in free radical substitution reactions
Propagation:
Reacts with a radical and produces another radical allowing chain reaction to occur.
Describe the third stage in free radical substitution
Termination:
Stop the reaction by consuming two radicals and breaking the chain reaction.
Why are radical substitutions not a good way of producing a specific product?
A wide range of products are made due to propagation as further substitution can occur. It can occur in different positions along a chain.
Define nucleophile
A species with a lone pair of electrons which is donates to a partially positive carbon to form a covalent bond.
What is a substitution reaction
One atom or group being replaced by another atom or group
What is a reflux and what is used to prevent volatile losses?
Process of a continuous evaporation and condensation without a loss of a reactant or product vapours.
A condenser is used to stop the escape of volatile components.
What happens during a nucleophilic substitution reaction
The lone pair of electrons on the nucleophile are attracted to the partially positive carbon on the haloalkane.
What is needed an aqueous alkali undergoes nucleophilic substitution
Reagents: NaOH (aq)
Conditions: Heat under reflux
Mechanism: Na+ spectator ion
Describe the nucleophilic reaction with a haloalkane and water
Reagent: Water
The reaction is much slower than using OH- ions.
Describe the reaction with haloalkanes and NH3 to form amines
Reagents: conc NH3 solution
Conditions: heat in sealed tube
Describe a method used to investigate the rate of hydrolysis of different haloalkanes
Mix the haloalkane with water and ethanol at 60 degrees C.
Add silver nitrate and start clock.
Time how long it takes for a ppt to form.
Why should you use ethanol in the hydrolysis of haloalkanes
Haloalkanes are insoluble in water but soluble in ethanol. Water is soluble in ethanol too so ethanol works as a mutual solvent.
Describe the strength of the bonds C-CL to C-I
Bonds weaken so less energy needed to break bonds and the reaction with nucleophiles is faster.
What are the observations of haloalkanes ppt with ethanol and water
CH3I:Yellow ppt immediately
Ch3Br: cream ppt after a few minutes
Ch3Cl: white ppt formed slowly
Ch3F: no change observed
What are the compositions of the troposphere and they’re abundancies
Nitrogen: 78%
Oxygen: 21%
Argon: 1%
CO2: 0.0339%
What is the effect on ozone in the stratosphere
Absorbs high energy UV and reduces skin cancer
What is the effect of ozone in the troposphere
Forms photochemical smog which is toxic and can cause respiratory problems.
What are the three equations of ozone
Formation:
O + O2 - O3
Breaking down:
O3 - O2 + O
Overall equation:
O2 + O = O3
Describe CFCS
Extremely stable compounds. They remain stable in atmosphere until they reach the stratosphere. They absorb high energy UV radiation which causes photodissociation. This releases chlorine radicals which can destroy Ozone.
What are the equations for CFCS and chlorine radicals
Formation: (photodissociation)
CCL2F2 - CF2CL + CL
Prop1: Cl + O3 - CLO + o2
Prop2: CLO + O - O2 + CL
Overall:
O3 + o - 2O2
What are the alternatives to CFCS
HCFCs:
- much less stable so broken down in troposphere
HFCs:
- Never release CL radicals
- C-F bonds too strong so F radicals aren’t formed
