CSe2 (carbon diselenide) has one carbon atom and two selenium atoms. In the lewis structure of CSe2, there are two double bonds around the carbon atom, with two selenium atoms attached to it, and on each selenium atom, there are two lone pairs.
Here’s how you can draw the CSe2 lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Hence, carbon has four valence electrons and selenium has six valence electrons.
Since CSe2 has one carbon atom and two selenium atoms, so…
Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of two selenium atoms = 6 × 2 = 12
And the total valence electrons = 4 + 12 = 16
- Second, find the total electron pairs
We have a total of 16 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 = 16 ÷ 2 = 8
- Third, determine the central atom
We have to place the least electronegative atom at the center.
Since carbon and selenium have the same electronegativity value, we can assume any one as the central atom, right?
But if we place selenium in the center and carbon outside, and calculate the formal charge, then we do not get the formal charges on atoms closer to zero.
And the structure with the formal charges on atoms closer to zero is the best lewis structure.
Hence, here we have to assume that the central atom is carbon.
Therefore, place carbon in the center and seleniums on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 8 electron pairs. And two C — Se bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.
Also remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell. And selenium is a period 3 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 seleniums.
So for each selenium, there are three lone pairs, and for carbon, there is zero lone pair because all six 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 carbon atom, formal charge = 4 – 0 – ½ (4) = +2
For each selenium atom, formal charge = 6 – 6 – ½ (2) = -1
Here, both carbon and selenium atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both carbon and selenium atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the selenium atom to make a new C — Se bond with the carbon atom as follows:
#5 Minimize Charges Again
Since there are charges on carbon and selenium atoms, again convert a lone pair of the selenium atom to make a new C — Se bond with the carbon atom as follows:
In the above structure, you can see that the central atom (carbon) forms an octet. Hence, the octet rule is satisfied.
Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of CSe2.
Next: AlBr3 Lewis Structure