The question
Name: ______________________ Date: ____________ Bonding and shape in chlorine oxyanions (10 points)
Experimental setup
Chlorine oxyanions
Chlorine forms several ions with oxygen. Two of them are the chlorite ion, ClO₂⁻, and the chlorate ion, ClO₃⁻. In both, Cl is the central atom bonded to each O atom. Chlorine is in period 3. Electronegativity values: Cl 3.2, O 3.4.
Measured Cl–O bond lengths: in ClO₂⁻ both bonds are 156 pm; in ClO₃⁻ all three bonds are 149 pm. A typical Cl–O single bond is about 170 pm.
(a) Determine the total number of valence electrons in the chlorite ion, ClO₂⁻. [1 point]
(b) Draw a complete Lewis diagram for ClO₂⁻ in which every atom has an octet. Show all lone pairs. [1 point]
(c) Calculate the formal charge on the Cl atom in your diagram from part (b). Show your work. [1 point]
(d) A student proposes a second diagram for ClO₂⁻ with one Cl=O double bond and one Cl–O single bond, in which Cl has two lone pairs. Justify, using formal charges, why the formal-charge criterion favors this diagram over the diagram in part (b). [2 points]
(e) The two Cl–O bonds in ClO₂⁻ have the same length, 156 pm, which is shorter than a typical Cl–O single bond. Explain this observation. [2 points]
(f) Identify the molecular geometry of ClO₂⁻ and estimate the O–Cl–O bond angle. Justify your answer in terms of electron domains. [2 points]
(g) The Cl–O bonds in ClO₃⁻ (149 pm) are shorter than those in ClO₂⁻ (156 pm). A student claims that this is because ClO₃⁻ has more oxygen atoms pulling on the Cl atom. Evaluate the claim, using bond order. (The preferred diagram of ClO₃⁻ has two Cl=O double bonds and one Cl–O single bond, with resonance among all three positions.) [1 point]