Lewis structure for the chlorite ion, ClO2, that obeys the octet rule, showing all non-zero formal charges. How many resonance structures for ClO2 that obey the octet rule are possible? A. none of the above B. three C. four D. one
The Correct Answer and Explanation is:
To determine the Lewis structure of the chlorite ion (ClO₂⁻), let’s break down the steps while following the octet rule and calculating the formal charges.
Step 1: Count Valence Electrons
- Chlorine (Cl) is in Group 17, so it contributes 7 valence electrons.
- Oxygen (O) is in Group 16, and each oxygen atom contributes 6 valence electrons. Since there are 2 oxygens, the total from oxygen is 12 valence electrons.
- The ion has a -1 charge, which means an additional 1 electron must be added.
Total valence electrons = 7 (from Cl) + 12 (from O) + 1 (from the charge) = 20 electrons.
Step 2: Drawing the Basic Structure
The central atom is chlorine (Cl), surrounded by two oxygen atoms. The chlorine atom will form single bonds with each oxygen atom, using 4 electrons (2 electrons per bond). This leaves us with 16 electrons to place.
Step 3: Placing Electrons Around Oxygen
Each oxygen atom needs to satisfy the octet rule. To do so, place 6 electrons (3 lone pairs) around each oxygen, which accounts for 12 electrons.
This leaves 4 electrons remaining, which should be placed as lone pairs on the chlorine atom.
Step 4: Assigning Formal Charges
- Chlorine: The chlorine atom has 7 valence electrons, and in the structure, it has 2 bonding electrons (from the bonds with oxygen) and 4 lone pair electrons. The formal charge on chlorine is calculated as: Formal charge on Cl=7−(2 bonding electrons+4 lone pair electrons)=7−6=+1\text{Formal charge on Cl} = 7 – (2 \text{ bonding electrons} + 4 \text{ lone pair electrons}) = 7 – 6 = +1Formal charge on Cl=7−(2 bonding electrons+4 lone pair electrons)=7−6=+1
- Oxygen: Each oxygen atom has 6 valence electrons, 2 bonding electrons, and 6 lone pair electrons. The formal charge on each oxygen is: Formal charge on O=6−(2 bonding electrons+6 lone pair electrons)=6−8=−1\text{Formal charge on O} = 6 – (2 \text{ bonding electrons} + 6 \text{ lone pair electrons}) = 6 – 8 = -1Formal charge on O=6−(2 bonding electrons+6 lone pair electrons)=6−8=−1
Thus, each oxygen has a formal charge of -1, and chlorine has a formal charge of +1.
Step 5: Resonance Structures
There are two possible resonance structures for the chlorite ion, where the double bond can switch between the two oxygen atoms. These structures obey the octet rule for chlorine and oxygen, and formal charges are distributed evenly across the atoms.
Final Answer: B. three resonance structures
There are 3 resonance structures, including those that switch the formal charges between the two oxygen atoms. Each resonance structure maintains the octet rule and keeps the formal charges balanced.
