[eternity119]

Hey everyone,
I really need your help. If anyone can solve any of these questions it would really really really *delete me* Thanks!

I am writing an exam soon, and still have problems solving the following questions, unfortunately i don't have any solutions to these practice questions, so I am having troubles with them:

1. State the names of the quantum numbers n and l as they apply to atomic orbitals. How do the energies of the orbital depend on n and l? Distinguish carefully between H and all other atoms, stating the reason fore the differences. On an energy level diagram sketch the relative energies of all the orbitals up to n=3 for both H and for a typical multielectron atom.

2. What is the difference between orbitals with the same n but different
values of l? Illustrate your answer with (a) electron contour drawings
and (b) electron density plots for the 2s and 2p atomic orbitals of the
H atom.

3. Estimate the heat of reaction when ethene is burned in oxygen to
produce carbon dioxide and water, given the following bond energies
(kJ mol-1). Is the reaction exothermic or endothermic?
C─H 411 C=C 602 O=O 494 C=O 1072 O─H 459

4. What is the molecular structure of SeF4?
What is the hybridisation at the central atom in SeF4?
Describe the bonding in SeF4 in terms of valence bond theory. [

5. Use VSEPR theory to deduce structures for the following molecules
or ions, clearly showing your reasoning in each case.
(i) IOF5 (ii) IO2F2
− (iii) IF5 (iv) IF4
−

6. Sulfur forms a compound with fluorine that has the stoichiometry SF6.
Briefly explain why an oxygen atom, although in the same Group as
sulfur in the periodic table, cannot form a fluoride of this
stoichiometry.

7. Classify the following oxides as either acidic or basic.
(a) BaO (b) P4O10
Produce a balanced chemical equation to describe the reaction of each
of these oxides with water.


Hypochlorite ions (ClO-), react with iodine (I2) yielding chloride ions
(Cl-) and iodate ions (IO3
-) as products.
Produce ion-electron half equations for the ClO-/Cl- and I2/IO3
-
processes and hence produce a balanced equation for the overall process.

9) Using as a guide the stoichiometry and the nature of the bonding
found for the fluorides of the Period 3 elements, Na through to Cl, consider
the fluorides of the following Period 4 elements :-
K, Ca, Ga, Ge, As, Se and Br.
Give the stoichiometry of the fluorides of these elements, and predict
the bonding (ionic, covalent, polar covalent) found in each, giving your
reasoning.

10) Acid rain has a dramatic effect on the environment. Discuss which
compounds have the greatest impact in the production of acidic rainfall.
Draw chemical structures for these compounds.

11) Draw Newman projection formulae of CH3CH2CH2I showing :
the most stable conformation
the least stable conformation

12) 1o, 2o and 3o alkyl bromides may react with nucleophiles by the SN1
or SN2 reaction mechanism. Indicate which mechanism is usual for
(i) 1o bromides
(ii) 3o bromides [2

13) Illustrate this by drawing out the appropriate mechanism (curly
arrows) for the reactions between:
CH3 CH2 CH2 CH2 Br and H3C C O
O
[4]
CH3
C
CH3
H3C Br and H2O

14) In the reaction between CH3CH2CH2Br and OH – a small amount of
a second product is produced (in addition to the major product,
CH3CH2CH2OH).
What is the structure of this product, and how does it arise ?

15) Draw a reaction mechanism for the following reaction.
H3C CH CH3
OH
+ H2SO4 H3C CH CH2

[UG]

1/2. n is the principle quantum number, l is the orbital quantum number. The energy of each orbital increases as the distance from the nucleus increases. If n was 2, l lies in the range 0 to (n-1). Therefore, n=2, l=0 and 1, this means the n=2 level gives rise to two sub-levels, one with l=0 and one with l=1. l defines a particular type of atomic orbital, i.e s,p,d and f. l=0 corresponds to an s orbital, l=1 a p orbital, l=2 a d orbital and l=3 an f orbital.

3. The enthalpy change is equal to the sum of the bonds broken minus the sum of the bonds formed.

4. Selenium tetrafluoride

5. Which one is the central atom? How many covalent bonds can it form (not just single, hint hint for i and ii)?

6. Hypervalent molecule
Think about the sizes of the two elements.

7. Barium oxide
Tetraphosphorus decaoxide reacts with water to form phosphoric acid
 

[UG]

8. Half of it is already here, you should be able to manage the other half.

9. Look at the electronegativity differences between fluorine and the period 4 elements, you should be able to predict the nature of the types of bonding.

10. http://en.wikipedia.org/wiki/Acid_rain#Emissions_of_chemicals_leading_to_acidification

11. The lowest-energy, most stable conformation is the one in which all of the C-H/C-I bonds are as far away from each other as possible. Here's how they look like: http://www.iupac.org/goldbook/N04134.pdf

12. Read Nucleophilic substitution in primary halogenoalkanes, it will explain it much better than I can.

13. Your diagram is a bit over the place  , you'll need to draw it again.

14. Not sure about this one  , you'll have to ask in the organic board.

15.http://www.chemguide.co.uk/mechanisms/elim/dhethanol.html
 

[Astrokel]

14. E2 reaction

[Johnny010]

Primary Alkyl Bromides tend to go via the SN2 mechanism pathway. There is little steric hinderence for the Nucleophile to attack the molecule from the 'backside' to form the nice planar looking transition state (more octahedral). Therefore the rate=k[alkylbromide][Nucleophile] which is a 2nd order reaction...notice the SN <b>2</b>.

Tertiary alkyl bromides tend to go via the SN1 mechanism (the bromine has to naturally 'dissociate' from the rest of the molecule). The bromine leaves, then a nucleophile can attack the carbon. The bromine loss step is the rate determining step (it doesn't matter how much nucleophile is in there, it can not attack untill the bromine has dissociated), therefore the rate equation is simply rate=[alkylbromide].

This is a first order reaction therefore the mechanism is known as an SN<b>1</b> mechanism.