HF (hydrogen fluoride) has one hydrogen atom and one fluorine atom. In the lewis structure of HF, there is a single bond between the hydrogen and fluorine atom, and on the fluorine atom, there are three lone pairs.
Here’s how you can draw the HF 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, hydrogen has one valence electron and fluorine has seven valence electrons.
Since HF has one hydrogen atom and one fluorine atom, so…
Valence electrons of one nitrogen atom = 1 × 1 = 1
Valence electrons of one fluorine atoms = 7 × 1 = 7
And the total valence electrons = 1 + 7 = 8
- Second, find the total electron pairs
We have a total of 8 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 = 8 ÷ 2 = 4
- Third, determine the central atom
Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.
Hence, here we have to assume that the central atom is fluorine.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 4 electron pairs. And one H — F bond is already marked. So we have to only mark the remaining three electron pairs as lone pairs on the sketch.
Also remember that hydrogen is a period 1 element, so it can not keep more than 2 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 atom is fluorine.
So for fluorine, there are three lone pairs, and for hydrogen, there is zero lone pair because all three 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 hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For fluorine atom, formal charge = 7 – 6 – ½ (2) = 0
Here, both hydrogen 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 (fluorine) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the stable lewis structure of HF.
Next: SCl2 Lewis Structure