SiCl2Br2 (dibromo dichlorosilane) has one silicon atom, two chlorine atoms, and two bromine atoms. In the lewis structure of SiCl2Br2, there are four single bonds around the silicon atom, with two chlorine atoms and two bromine atoms attached to it, and on each chlorine and bromine atom, there are three lone pairs.
Here’s how you can draw the SiCl2Br2 lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Hence, silicon has four valence electrons, both chlorine and bromine have seven valence electrons.
Since SiCl2Br2 has one silicon atom, two chlorine atoms, and two bromine atoms, so…
Valence electrons of one silicon atom = 4 × 1 = 4
Valence electrons of two chlorine atoms = 7 × 2 = 14
Valence electrons of two bromine atoms = 7 × 2 = 14
And the total valence electrons = 4 + 14 + 14 = 32
- Second, find the total electron pairs
We have a total of 32 valence electrons. And when we divide this value by two, we get the value of total electron pairs.
Total electron pairs = total valence electrons ÷ 2
So the total electron pairs = 32 ÷ 2 = 16
- Third, determine the central atom
We have to place the least electronegative atom at the center.
Since silicon is less electronegative than chlorine and bromine, assume that the central atom is silicon.
Therefore, place silicon in the center and chlorine and bromine on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 16 electron pairs. And four bonds are already marked. So we have to only mark the remaining twelve electron pairs as lone pairs on the sketch.
Also remember that both (silicon and chlorine) are the period 3 elements, so they can keep more than 8 electrons in their last shell. And bromine is a period 4 element, so it can keep more than 8 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are chlorines and bromines.
So for each chlorine and bromine, there are three lone pairs, and for silicon, there is zero lone pair because all twelve electron pairs are over.
Mark the lone pairs on the sketch as follows:
#3 Mark Charges
Use the following formula to calculate the formal charges on atoms:
Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons
For silicon atom, formal charge = 4 – 0 – ½ (8) = 0
For each chlorine atom, formal charge = 7 – 6 – ½ (2) = 0
For each bromine atom, formal charge = 7 – 6 – ½ (2) = 0
Here, the atoms do not have charges, so no need to mark the charges.
And in the above structure, you can see that the central atom (silicon) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the stable lewis structure of SiCl2Br2.
Next: SOCl2 Lewis Structure