OH- Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair and Detailed Facts

OH- ion is a diatomic anion known as hydroxide ion. It is basic in nature. It is also known as hydroxyl group while determining functional group of any structure.

Hydroxide (OH-) ion is occurs naturally in water. It is basically electrically neutral molecule. It can ionizes itself to get H+ ions (cations) which is a major constituent in acid formation. This ion can produce salts some of which can dissociates in aqueous solutions. Here, in this editorial we are learning about OH- lewis structure and its detailed facts.

How to draw lewis structure for OH-?

Following are the points mentioned to draw the lewis structure of any molecule:

  1. Counting of total valence electrons available on structure.
  2. Central position is occupied by the element with lowest electronegativity.
  3. Make connection of bonding within all elements present in structure.

Chemical formula for hydroxide ion is OH-.

Molecular weight of OH- is 17.007 g mol-1.

Molecular geometry of OH- is linear in shape.

OH- has sp hybridization.

OH- is polar in nature.

In OH- ion, only two elements involved i.e. it is diatomic containing one oxygen and one hydrogen atoms. There is a single covalent bond between the O and H atoms. Oxygen atom carrying -1 charge on it which shows the generally as whole charge on OH- ion. In OH- lewis structure there are lone electron pairs present on O atom.

  • Counting of total valence electrons available on OH- ion structure.

Now we will calculate the total valence electrons present on hydroxide (OH-) ion. OH- ion has only two elements hydrogen atom and oxygen atom. Hydrogen atom belongs to the 1st group of periodic table and oxygen atom belongs to the 16th group of periodic table. Therefore, hydrogen atom contains one valence electron and oxygen atom contains six valence electrons.

Also during valence electrons calculation of OH- ion we have to add extra one electron for the minus (-) charge on OH- group.

Therefore, Oxygen atom valence electrons = 6 x 1 (O) = 6

                  Hydrogen atom valence electrons = 1 x 1 (H) = 1

      Add one more electron for negative charge present on OH-

Hence, OH- ion has total valence electrons = 6 (O) + 1 (H) + 1 (-) = 8

So, OH- lewis structure has eight total valence electrons.

Now, as we have total 8 valence electrons on OH- lewis structure, so we have to calculate the total electron pairs. For that we have to divide it by 2 we get.

Total electron pairs = Total valence electrons on OH- ion / 2 = 8 / 2 = 4

Therefore, we have to otal four electron pairs.

OH 1
OH- lewis structure showing valence electrons
  • Central position is occupied by the element with lowest electronegativity.

This point is not applied in case of OH- lewis structure because it has only two atoms present and they cannot take central position of structure. Even the central atom should attached with at least two more atoms and there is only single bond is present within oxygen and hydrogen atom.

So, we can place oxygen and hydrogen atom beside each other in OH- lewis structure.

  • Make connection of bonding within all elements present in structure.

Now we have to make a link between the two elements present in OH- lewis structure by making a bond between them as shown in the following image.

OH 2
OH- lewis structure showing bond between O and H atom

OH- lewis structure octet rule

In the above OH- lewis structure we already make a single covalent bond between O and H atom. So, two valence electrons get involved in bonding between O and H atom out of total eight valence electrons. Now, we are left with only six valence electrons for electron distribution to complete the octet of O atom.

As we already know that hydrogen atom has the capacity to have only two electrons in its valence shell. So, hydrogen atom already filled its valence orbital with two bonding electrons of O-H single covalent bond, as single bond consists of two valence electrons.

Now, we have to distribute all the remaining six valence electrons i.e. three electron pairs with oxygen atom only. So we get the following structure.

OH 3
OH- lewis structure applying octet rule

From the above structure we can see that the hydrogen atom has two bonding electrons means its valency is satisfied and the oxygen atom has total eight electrons means it has a complete octet with three lone pairs and one bond pair electrons.

OH- lewis structure formal charges

Any lewis structure is more stable if it has a small formal charge on it. To calculate the formal charge on any molecule or structure there is a formula as follows:

Formal charge = (valence electrons – non-bonding electrons – ½ bonding electrons)

Now we have to calculate the formal charge for hydroxide ion i.e. OH- lewis structure. So first let us calculate formal charge on hydrogen atom.

Hydrogen atom: Valence electrons on Hydrogen atom = 01

                           Non-bonding electrons on Hydrogen atom = 00

                           Bonding electrons with Hydrogen atom =02

Formal charge on Hydrogen atom = (1 – 20– 2/2) = 00

Thus, hydrogen atom has zero formal charge on it.

Oxygen atom:Valence electron on oxygen atom = 06

                        Non-bonding electron pair on oxygen atom = 06

                        Bonding electrons on oxygen atom =2

Formal charge on oxygen = (06 – 06 – 2/2) = -1

Hence, the oxygen atom of OH- ion has -1 formal charge

So, in OH- lewis structure hydrogen has zero formal charge and oxygen has -1 formal charge.

OH- lewis structure lone pairs

As we see in the above structure, there is a one bond between hydrogen and oxygen atoms containing two valence electrons i.e. they become bond pair. The remaining electron pairs which then goes on oxygen atoms to complete its octet. As the hydrogen atom has two electrons in its bond pair and its valence shell is gets filled as it cannot accept more than two electrons.

So, all the remaining three electrons pairs will goes to oxygen atom. Thus the oxygen atom of OH- lewis structure has total three lone electron pairs.

OH- lewis structure shape

Any lewis structure can be determined by the help of representations of VSEPR theory if any molecular diagram has more than two atoms in it. Here, in OH- lewis structure involvement of two elements are there i.e. oxygen and hydrogen. OH- ions follow the VSEPR theory generic formula AXE.

So, according to VSEPR theory geometry of ions the OH- shows linear shape. In OH- lewis structure, there is both the valence shell of O and H atoms get filled with sufficient electrons as per its capacity. Hydrogen has two electrons and oxygen atom has six electrons but if we count bond pairs with O atom so it has complete octet with eight electrons. So, after bonding there is three lone pair electrons remain on O atom.

So, there is no repulsion between any bond pair and lone pair of electrons in OH- lewis structure due to the presence of single covalent bond between O and H atoms. Therefore, OH- lewis structure has linear shape.

OH 5
OH- lewis structure showing linear shape

OH- Hybridization

Until now we have discussed about OH- lewis structure bonding, lone pairs, molecular geometry, shape and formal charges. Now, let us discuss about its hybridization.

If we look upon the OH- lewis structure we have discussed yet, we can see that there is no double or triple bond present so there is no pi-bond in OH- ion. It has only one single covalent bond within H and O atoms i.e. presence of only sigma (σ) bond within it and there are three lone electron pairs are present on one oxygen atom.

Any structure or molecules hybridization is depend upon its steric number of central atom. The OH- hybridization is depend on both atoms O and H atoms steric number as there is no central atom present.

Steric number is the sum of total no. of bonded atoms associated with central element and its lone electron pair present on it.

Steric number of OH- = (no. of bonded elements or atoms attached central element + central atom having lone pair of electrons)

As there is no middle element in OH- lewis structure, there is only one bonded atom and three lone electron pairs are present.

So, the Steric number for OH- ion = 1 (bonded H atom) + 3 (lone pair electron of O)

Therefore, the oxygen atom shows sp3 hybridization in OH- lewis structure. But if we see the shape of OH- ion which has linear shape than it should have sp hybridization according to its shape. Basically hybridization of OH- ion is depends upon the molecules attached to it for ex. CH3-OH, H-OH, etc.

Means if the geometry of structure or molecule is linear then OH- is sp hybridised, if trigonal planar then it is sp2 hybridised, if it is tetrahedral then it is sp3 hybridised, and so on depends upon the molecule containing OH- ion.

OH- lewis structure resonance

The resonance structure of any molecule shows the variation of distribution of electrons in the same molecule. There are some rules to draw the resonance structure of any molecule is that, the molecule should contain multiple bonds in its structure like double or triple bonds and also the connected atoms have at least one electron lone pair. If the molecule accomplished all these conditions then it has a possible resonance structure.

In case of OH- lewis structure, the oxygen atom contain three lone pairs with one negative charge on it and linked with hydrogen with a single covalent bond, which shows the more stable form of OH- lewis structure. But generally while writing the chemical formula for hydroxide ion the negative charge gets shown on whole molecule.

The negative charge on oxygen atom is due the completion of octet (presence of eight) electrons. So, the OH- ion does not show any typical resonance structure as there is no multiple bond and do not obey the resonance structure rules. But we can draw the comparative structure to show the charge transformation.

OH- lewis structure
OH- lewis structure showing stable structure and charge on whole OH- ion

OH- polar or nonpolar

Now, let we learn about the non-polar / polar nature of OH- ion. The electronegativity of oxygen atom is 3.44 and the electronegativity of hydrogen atom is 2.2. there is a huge difference in electronegativity of oxygen and hydrogen molecules.

As we talk about the polarity of OH- ion, the OH- ion shows polar nature mostly if present in any molecule. If we see the example of methanol and water, in which the OH- ions are present in its structure. In both methanol and water it shows polar nature as the oxygen atom is more electronegative than hydrogen atom.

Therefore, due to more electronegativity of O atom, the shared electrons makes crowd on the O atom, which results in the creation of partial negative charge on O atom and partial positive charge on H atom. Means the whole electron density attracts by O atom towards itself and the polarity creates on O-H bond.

Thus the OH- ion or lewis structure shows the polar nature.

OH- lewis structure bond angle

As we already discussed earlier about the shape and hybridization of OH- lewis structure. The hybridization and shape of OH- ion depends upon the nature of compound or molecule in which the OH- ion is present.

As per the shape of OH- ion discussed above is basically linear. So, its bond angle should have to be nearly 180 degree. But the bond angle of Oh- ion is actually depends upon the structure and orientation of that particular molecule in which the OH- ion is present.

OH- lewis structure electron geometry

The electron geometry of OH- ion shows the presence of eight electrons in it. All the eight electrons is surrounded to oxygen atom means all the electron density cover to oxygen atom. Eight valence electrons it means four electron pairs. Thus, in OH- ion there is four electron densities surrounding O atom.

So, we consider the tetrahedral shape for electron geometry of OH- ion. But still it depends on electron geometry of the molecule in which the OH- is present.

OH 1 1
OH- lewis structure showing its electron geometry

OH- Uses

  • Caustic soda which is the form of sodium hydroxide are used in paper and pulp industry, textile industry, potable drinking water, soap bars and detergents and as a septic and wash basin drain cleaner.
  • In fuel cells hydroxides are used.
  • Hydroxide ions are used in disinfectants.
  • In agriculture potassium hydroxide is used.
  • Limonite and goethite which are low grade brown iron ore is produced by the use of iron hydroxides.
  • Hydroxides are used as food preservatives to protect the food from various bacteria’s and moulds.
  • In extractation of alumina hydroxide is used.
  • Aluminium hydroxides are used in aluminium ore bauxite.

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