SiF4 (silicon tetrafluoride) has one silicon atom and four fluorine atoms. In the lewis structure of SiF4, there are four single bonds around the silicon atom, with four fluorine atoms attached to it, and on each fluorine atom, there are three lone pairs.
Here’s how you can draw the SiF4 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 and fluorine has seven valence electrons.
Since SiF4 has one silicon atom and four fluorine atoms, so…
Valence electrons of one silicon atom = 4 × 1 = 4
Valence electrons of four fluorine atoms = 7 × 4 = 28
And the total valence electrons = 4 + 28 = 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 fluorine, assume that the central atom is silicon.
Therefore, place silicon in the center and fluorines on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 16 electron pairs. And four Si — F bonds are already marked. So we have to only mark the remaining twelve electron pairs as lone pairs on the sketch.
Also remember that silicon is a period 3 element, so it can keep more than 8 electrons in its last shell. And fluorine is a period 2 element, so it can not keep more than 8 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are fluorines.
So for each fluorine, 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 fluorine atom, formal charge = 7 – 6 – ½ (2) = 0
Here, both silicon and fluorine 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 SiF4.
Next: CH3F Lewis Structure