Question

1. Which of the following represent configurations of thallium ions in compounds? Explain your decision in each case.
a. Ti 2+ [Xe]4f 14 5d 10 6p 1
b. Ti 3+ [Xe]4f 14 5d 10
c. Ti 4+ [Xe]4f 14 5d 9
d. Ti + [Xe]4f 14 5d 10 6s 2

2. Draw the Lewis structures of the following compounds and indicate which structures do not obey the octet rule.
a. CH3CHO
b. F2CO
c. Cl2SO
d. SiF 6-
e. PH 4+
f. PO4 3-
g. ClO2

3. Draw Lewis structures for the following species, indicating the formal charges and resonance structures, where applicable.
a. HOSO3 -
b. H2NCN
c. FCO2 -
d. S2N2
e. N2O3 2-
f. H2CSF4

4. Describe the electron group geometry and molecular structure of the following species.
a. SiF6 2-
b. PF5
c. SF4
d. XeF4

5. Lactic acid has the formula CH3CH(OH)COOH. Draw the molecule and indicate the various bond angles

6. Predict the geometry of the following ions, using VSEPR model.
a. SnCl5 -
b. PF6 -
c. ClF2 -
d. IF4 -

Answer 1

#1: Metals are converted to cations by donating electrons so as to achieve either ful-filled or half-filled stable configuration.

Among the given cations, only Tl⁺ has ful-filled s-orbital configuration and Tl³⁺ has ful-filled d-orbital configuration. Hence options (b) and (d) are correct.  

#2: While drawing Lewis structure, first we count total number of valence electrons in all the atoms in a molecule. Then we fill these valence electrons in such a way that each atom except H complete octet.

Since H requires 2 electrons to fulfilled electronic configuration, we need to fill 2 electrons for H.

(a): CH3CHO: C, O and H have respectively 4, 6 and 1 valence electrons.

Hence total valence electrons = 2*4 + 1*6 + 4*1 = 18

Now we have to fill 18 electrons so as to complete octet for each of C and O atoms.

Among the above Lewis structures, Si atom in SiF₆^2- has 2*6 = 12 valence electrons.

Hene Si doesn't obey octet rule.