Question

draw a possible resonance structure for the bromate ion (bro₃⁻) with minimal formal charge. include all lone pair electrons and nonzero formal charges. click and drag to start drawing a structure.

Explanation:

Step1: Calculate valence electrons

Bromine (Br) has 7 valence electrons and oxygen (O) has 6 valence electrons. For $BrO_3^-$, the total number of valence electrons is $7 + 3\times6+1=26$.

Step2: Determine the central atom

Bromine is the central atom. Connect the oxygen atoms to the bromine atom with single - bonds first. Each single - bond uses 2 electrons, so 6 electrons are used in 3 single - bonds. Remaining electrons are $26 - 6=20$.

Step3: Distribute remaining electrons

Distribute the remaining 20 electrons as lone - pairs on the oxygen atoms first. Each oxygen atom can get 3 lone - pairs (6 electrons in total for each oxygen). After distributing lone - pairs on oxygen atoms, all 20 electrons are used. But to minimize formal charge, we can form a double - bond between bromine and one of the oxygen atoms.
The formal charge on an atom is calculated as $FC = V - N - \frac{B}{2}$, where $V$ is the number of valence electrons, $N$ is the number of non - bonding electrons, and $B$ is the number of bonding electrons.
For the structure with a double - bond:

• On the double - bonded oxygen: $V = 6$, $N = 4$, $B = 4$, $FC=6 - 4-\frac{4}{2}=0$.
• On the single - bonded oxygen atoms: $V = 6$, $N = 6$, $B = 2$, $FC=6 - 6-\frac{2}{2}=- 1$.
• On bromine: $V = 7$, $N = 2$, $B = 8$, $FC=7 - 2-\frac{8}{2}=+1$.

The resonance structure will have the double - bond moving between the three oxygen atoms.

The resonance structure has Br as the central atom, with two Br - O single - bonds and one Br = O double - bond. Each oxygen has 2 or 3 lone - pairs depending on whether it is single - or double - bonded to Br, and the overall ion has a negative charge.

Answer:

Draw a structure with Br as the central atom. Connect two oxygen atoms to Br with single - bonds and one oxygen atom to Br with a double - bond. Place 3 lone - pairs on each of the single - bonded oxygen atoms and 2 lone - pairs on the double - bonded oxygen atom. Indicate the overall negative charge on the ion.