Simple Method for writing Lewis Structures for bromate BrO3- #24

A simple procedure for writing Lewis structures is given in a previous article entitled “Lewis Structures and the Octet Rule”. Relevant worked examples were given in the following articles: Examples #1, #2, #3 , #4, #5, #6,  #7,  #8, #9, #10, #11, #12, #13, #14,  #15, #16, #17, #18, #19, #20, #21 , #22 and  #23.

Let us consider the case of  BrO₃^-. Bromates are formed by many different ways in municipal drinking water, The most common is the reaction of Br^- with ozone:

                                                           Br^-  + O₃ →   BrO₃^-

In waters containing bromide (Br^-), such as those found in coastal regions subject to salt water intrusion, a disinfection by-product of the ozonation treatment of the water is the bromate ion BrO₃^-.
 The bromate ion is very carcinogenic with an estimated lifetime cancer risk 1:10000 for a concentration of 5 ppb. Several methods are used for the determination of bromate in drinking waters including an LC-ICP-MS method.
 

Step 1: Connect the atoms with single bonds. The central atom is the bromine atom.

Step 2: Calculate the # of electrons in π bonds (multiple bonds) using formula (1): 

Where n in this case is 4 since BrO₃^- consists of four atoms.

Where V = (7 + 6 + 6 + 6 ) – (-1) = 26  

Therefore, P = 6n + 2 – V = 6 *4 + 2 – 26 = 0     So, there are no π electrons in BrO₃^- and the structure in Step 1 is the Lewis structure. However, let us see the charge on the atoms.

Step 3 & 4: The Lewis structure for BrO₃^-  including charge is as follows:

Figure 1: Lewis structures for BrO₃^- . Structure 3 has the most reasonable distribution of formal charges.