What is the Charge of OH (Hydroxide ion)? And Why?

The Charge of OH (Hydroxide ion) is 1-.

But the question is how can you find the charge on OH (hydroxide ion)?

Well there are 2 methods by which you can find the charge of OH.

Lets dive right into these methods one by one.

You can also refer to the below video from which you will learn to find charge of any ion.

Method 1: By looking at what it is bonded to

The charge of OH (Hydroxide ion) can be found out by looking at what it is bonded to.

So let’s take some examples of compounds that contain OH; like NaOH, Al(OH)₃, etc.

Example 1: NaOH
In NaOH, the OH is bonded to Sodium (Na).
You know that the ionic charge of Na is 1+.
So you can easily say that the charge of OH should be 1-, then only it will get canceled out.
Hence the charge of OH in NaOH is 1-.

Example 2: Al(OH)₃
In Al(OH)₃, the OH is bonded to Aluminum (Al).
And again, you know that the ionic charge of Al is 3+.
So here also you can easily say that the charge of OH should be 1-, then only it will get canceled out.
Hence the charge of OH in Al(OH)₃ is 1-.

As seen from the above examples,
The charge of OH is 1-.

In this way, you can easily find the charge of OH by looking at what it is bonded to.

Method 2: By calculating the formal charge using lewis structure

In order to calculate the formal charge on OH (Hydroxide ion), you should know the Lewis dot structure of OH (Hydroxide ion).

Here is the lewis structure of OH.

Now using the above lewis structure of OH, you have to find the formal charge on each atom that is present in the OH molecule.

For calculating the formal charge, you need to remember this formula;

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

You can see the bonding and nonbonding electrons of OH from the image given below.

So now let’s calculate the formal charge on each individual atom present in OH.

Formal charge on Oxygen atom:
Valence electrons = 6 (as it is in group 16 on periodic table) ^[1]
Nonbonding electrons = 6
Bonding electrons = 2

So according to the formula of formal charge, you will get;

Formal charge on Oxygen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 6 – 6 – (2/2) = 1-

So the formal charge on oxygen atom is 1-.

Formal charge on Hydrogen atom:
Valence electron = 1 (as it is in group 1 on periodic table) ^[2]
Nonbonding electrons = 0
Bonding electrons = 2

So according to the formula of formal charge, you will get;

Formal charge on Hydrogen = Valence electrons – Nonbonding electrons – (Bonding electrons)/2 = 1 – 0 – (2/2) = 0

So the formal charge on hydrogen atom is 0.

Now let’s put all these charges on the lewis dot structure of OH.

So there is overall 1- charge left on the entire molecule.

This indicates that the OH (Hydroxide ion) has 1- charge.

I hope you have understood the above calculations of OH (Hydroxide ion). But for your tests, you don’t need to remember the entire calculations. You should just try to remember that OH has 1- charge.

Check out some other related topics for your practice.

Related topics:
Charge of Oxygen (O)
Charge of Lead (Pb)
Charge of Potassium (K)
Charge of Calcium (Ca)
Charge of Iron (Fe)