Chemistry Olympiad Training Program Sec 4/2010
Further Problems
Electron dot-cross and line-bond structure practice
1. Draw the dot-and-cross diagrams of the following species:
a) BaO b) H2S c) CS2 d) HCN e) NaH f) NO
g) N2O5 h) H2SO4 i) [AlCl4]- j) [ClO3]- k) H2O2 l) NaOH
2. Draw a line-bond structure for each of the following:
a) SiF4 b) SeCl2 c) COF2 d) PH4+ e) C2F2 f) SbH3
g) HNO3 h) IF5 i) HCO3- j) AsF4 k) BeCl2 l) XeF4
3. Draw line-bond structures for the following nitrogen oxides.
(a) NO (b) NO2 (c) N2O (d) N2O4 (e) N2O5
4. Discuss the nature of the bonding present in solid NH4Cl.
5. It is known that AlCl3 and N(CH3)3 react readily to form an adduct. [An adduct is the result of the direct combination of 2 separate molecules].
a) Explain why these two molecules form a product when they react in a molar ratio of 1:1.
b) Draw the dot-and-cross diagram and describe the shape of the adduct.
6. Molten beryllium chloride reacts with chloride ion from molten NaCl to form the BeCl42- ion, in which the Be atom attains an octet. Show the ionic reaction with line-bond structures.
7. *Question to be handed up*
AlF3 has high melting point of 1275oC and AlCl3 has melting point of only -150oC.
a) Draw the dot and cross diagrams to illustrate the bonding in AlCl3 and AlF3.
b) Explain the difference in the melting point between AlCl3 and AlF3.
c) State the difference in one other physical property (besides melting point and boiling point) for the two compounds, AlCl3 and AlF3.
d) Aluminium chloride catalyses certain reactions by forming carbocations, C2H5+, with chloroethane as shown in the following equation.
C2H5Cl + AlCl3 à C2H5+ + AlCl4-
Explain, in terms of bonding, how AlCl4- is formed.
Lesson 2 – In-class Practice Exercises
Shapes Challenge
8. For each of the following species, deduce the shape and bond angles:
(a) SO2 (b) NCl3 (c) XeF3+ (d) SbF6–
(e) AlCl3 (f) NH4+ (g) BeCl2 (h) SnCl2
(i) PCl5 (j) BrCl5 (k) O3 (l) PH3
(m) ICl4– (n) SO3 (o) Cl2O (p) HNO3
(q) H3O+ (r) ClF4– (s) SF4 (t) BrF3
(u) NO2 (v) N2O (w) N2O4 (x) N2O5
(y) SbF5 (z) I3– (aa) N3–
9. Deduce the shape and bond angles in the following compounds of Xenon:
(a) XeF4 (b) XeOF2 (c) XeOF4 (d) XeO2F2
(e) XeO3F2 (f) XeO3 (g) XeF2
10. Deduce the shape and bond angles in the following organic molecules:
(a) CH3OH (b) N(CH3)3 (c) C2H4 (d) H2CO
(e) CCl2F2 (f) C2H6 (g) C2H2 (h) CH3CO2H
11. AlCl3 is an electron deficient species. In the vapour phase, the molecule resolves this deficiency by forming dimers, Al2Cl6. Suggest the structure of the dimer, stating its shape and bond angles.
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