H2O (water) has two hydrogen atoms and one oxygen atom. In the lewis structure of H2O, there are two single bonds around the oxygen atom, with two hydrogen atoms attached to it, and on the oxygen atom, there are two lone pairs.
Here’s how you can draw the H2O 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 oxygen has six valence electrons.
Since H2O has two hydrogen atoms and one oxygen atom, so…
Valence electrons of two hydrogen atoms = 1 × 2 = 2
Valence electrons of one oxygen atom = 6 × 1 = 6
And the total valence electrons = 2 + 6 = 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 oxygen.
Therefore, place oxygen in the center and hydrogens on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 4 electron pairs. And two O — H bonds are already marked. So we have to only mark the remaining two 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 oxygen 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 hydrogens. But no need to mark on hydrogen, because each hydrogen has already two electrons.
So for oxygen, there are two lone pairs.
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 each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For oxygen atom, formal charge = 6 – 4 – ½ (4) = 0
Here, both hydrogen and oxygen atoms do not have charges, so no need to mark the charges.
And in the above structure, you can see that the central atom (oxygen) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the stable lewis structure of H2O.
Next: N2 Lewis Structure