OH- Lewis Structure in 6 Steps (With Images)

So you have seen the above image by now, right?

Let me explain the above image in short.

OH- (hydroxide ion) lewis structure has one oxygen atom (O) and one hydrogen atom (H) which contain a single bond between them. There are 3 lone pairs on the Oxygen atom (O). There is a -1 formal charge on the Oxygen atom (O).

If you haven’t understood anything from the above image of OH- (hydroxide ion) lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of OH- ion.

So let’s move to the steps of drawing the lewis structure of OH- ion.

Steps of drawing OH- lewis structure

Step 1: Find the total valence electrons in OH- ion

In order to find the total valence electrons in a OH- (hydroxide ion), first of all you should know the valence electrons present in a single oxygen atom as well as hydrogen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of oxygen as well as hydrogen using a periodic table.

Total valence electrons in OH- ion

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. [1] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

→ Valence electrons given by hydrogen atom:

Hydrogen is group 1 element on the periodic table. ^[2] Hence the valence electron present in hydrogen is 1.

You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.

Hence, 

Total valence electrons in OH- ion = valence electrons given by 1 oxygen atom + valence electrons given by 1 hydrogen atom + 1 more electron is added due to 1 negative charge = 6 + 1 + 1 = 8.

Step 2: Select the central atom

Here the given ion is OH- ion. It has only two atoms, so you can select any of the atoms as a center atom.

(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)

Let’s assume the oxygen atom as a central atom (Because we have to keep hydrogen outside in any lewis structure).

Step 3: Connect each atoms by putting an electron pair between them

Now in the OH molecule, you have to put the electron pairs between the oxygen atom (O) and hydrogen atom (H).

This indicates that the oxygen (O) atom and hydrogen (H) atom are chemically bonded with each other in a OH molecule.

Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.

Now in this step, you have to check the stability of the outer atom.

Here in the sketch of OH molecule, we have assumed the oxygen atom as a center atom. So the hydrogen is the outer atom.

Hence you have to make the hydrogen atom stable.

You can see in the below image that the hydrogen atom is forming a duplet and hence it is stable.

Also, in step 1 we have calculated the total number of valence electrons present in the OH- ion.

The OH- ion has a total 8 valence electrons and out of these, only 2 valence electrons are used in the above sketch.

So the number of electrons which are left = 8 – 2 = 6.

You have to put these 6 electrons on the oxygen atom in the above sketch of OH molecule.

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom

In this step, you have to check whether the central oxygen atom (O) is stable or not.

In order to check the stability of the oxygen (O) atom, we have to check whether it is forming an octet or not.

You can see from the above picture that the oxygen atom is forming an octet. That means it has 8 electrons.

And hence the oxygen atom is stable.

Now let’s proceed to the final step to check whether the lewis structure of OH is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of OH.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on the oxygen atom (O) as well as hydrogen atom (H) present in the OH molecule.

For calculating the formal charge, you have to use the following formula;

Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons

You can see the number of bonding electrons and nonbonding electrons for each atom of OH molecule in the image given below.

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 2
Nonbonding electrons = 6

For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0

Formal charge	=	Valence electrons	–	(Bonding electrons)/2	–	Nonbonding electrons
O	=	6	–	2/2	–	6	=	-1
H	=	1	–	2/2	–	0	=	0

From the above calculations of formal charge, you can see that the oxygen (O) atom has -1 charge and the hydrogen (H) atom has 0 charge.

So let’s keep these charges on the respective atoms in the OH molecule.

This overall -1 charge on the OH molecule is represented in the image given below.

In the above lewis dot structure of OH- ion, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of OH- ion.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

N2H2 lewis structure	CH3Cl lewis structure
HBr lewis structure	N2H4 lewis structure
CH3NH2 lewis structure	SiO2 lewis structure