Lewis structure, Hybridization, and Molecular Geometry of CH3OH

What is CH3OH?

CH3OH is a chemical compound with the formula C H3-OH. It consists of 1 carbon atom, 3 hydrogen atoms, and 1 hydroxyl group (OH). The name of this chemical is derived from the common name of the alkyl group. CH3OH has alkyl group methyl (CH3OH). Thus, its name is methyl alcohol or methanol. The general name for CH3OH is wood alcohol.

Methyl alcohol has characteristic properties. It is a light, volatile, and colorless compound. It is flammable and has a distinctive odor. It is also poisonous to humans. Ingesting 10ml of methanol can make you permanently blind.

It is used as a fuel and an antifreeze, in the production of hydrocarbons and solvents, and the synthesis of some other compounds such as formaldehyde.

To understand how CH3OH. is formed, you must know how you can draw the Lewis structure and find out the molecular geometry. You must also know how to calculate the hybridization state of the molecule.

Lewis structure CH3OH

A Lewis structure or an electron dot structure is a simple representation of the bonding between molecules and ions. It is shown in terms of the shared pair of electrons. The Lewis structure of a compound assists in visualizing the valence electrons, and whether they exist as lone pairs or in bonds.

A Lewis structure is drawn with the help of the octet rule.

The octet rule says that an atom is the most stable when it has eight electrons in its outermost shell. Oxygen, Nitrogen, Carbon, and Halogens tend to follow this rule. When aiming to achieve the octet rule, make sure that the atom has 8 electrons in its outermost shell.

The end goal of making a Lewis structure is to identify the lone pairs of electrons and to help determine how those electrons would be bonded.

The first step is — you need to calculate the number of valence electrons in the molecule.

Usually, many students confuse between valence electrons and valency. Here’s the difference.

The number of valence electrons in an atom is the number of electrons in its outermost shell.

On the other hand, the valency of an element is the number of electrons it needs to lose, or gain, to become stable. For example, O has 6 electrons in its outermost shell. Thus its valency is 2. The oxygen atom has to bond with 2 electrons to become stable.

Let’s find the number of valence electrons for CH3OH.

In CH3, the C atom has 4 valence electrons because it has 4 electrons in its outermost shell. H each has a 1 valence electron.

CH3 has 4 + 1*3=7 valence electrons.

In the OH group, the O atom has 6 valence electrons. H again has 1 valence electron.

OH has a total of 6+1 = 7 valence electrons.

The total number of valence electrons in CH3OH is 7+7=14

Let’s see how we arrive at the Lewis structure of CH3OH.

Fig 1. Lone pairs and bonds

Fig 1 shows us how the bonding of CH3OH is done.

If you remember C has a valency of four. As per the octet rule, four valence electrons of C need four other electrons to form pairs. Three of these come from hydrogen atoms. The other electron comes from oxygen, bonding the C atom with O.

Therefore C now has 8 electrons in its outermost shell.

The oxygen atom on the other hand also achieves the octet rule, although not in the same way.

One electron from Oxygen bonds with one electron C, one electron bonds with one electron hydrogen, making two pairs of electrons. Still, 4 electrons are left in the valence shell of Oxygen. These electrons come together to form lone pairs.

Now, oxygen has achieved the octet rule. The two pairs of bonds (with C and H) and the two pairs of lone pairs together provide 8 electrons in Oxygen’s outermost shell.

Fig 2. Lewis structure CH3OH.

The Lewis structure of CH3OH depicts how valence electrons have come together to form the chemical.

There are 14 electrons depicted in Fig 2 which help Oxygen and Carbon achieve the octet rule, and thus completing the Lewis structure and diagram.

CH3OH Molecular Geometry

The molecular geometry of a compound is the 3-D representation of the atoms in the molecule. It also depicts the shape and bonds in the molecule.

Below is the molecular geometry of CH3OH.

CH3OH molecular geometry (Source: Pubchem)

The grey atom is a carbon atom. The red one is oxygen. The white atoms are hydrogen.

The molecular geometry of CH3OH is different than expected.

Can you guess why? Find out in the paragraph below.

Before that, let’s find the hybridization state of CH3OH.

CH3OH Hybridization

The hybridization state of a molecule is usually calculated by calculating its steric number.

The steric number of an atom is equal to the number of sigma bonds it has plus the number of lone pairs on the atom. There are exceptions where calculating the steric number does not give the actual hybridization state. That is not the case here.

To know the kind of hybridization CH3OH has, take a look at the structure of CH3OH.

Notice here that the C atom has 4 sigma bonds. We can also say that C has 4 attached atoms (3 Hydrogen, 1 Oxygen). Thus, there is a total of 4 sigma bonds.

The steric number of C here turns out to be 4 = 4 sigma bonds + 0 lone pairs.

Since C has the steric number 4, we can conclude CH3OH has sp3 hybridization.

Another way of arriving at the hybridization would be to look at the electronic configuration of the carbon atom in CH3OH.

C has the electron configuration 1s2 2s2 2p2

In its electron configuration, the C atom has 2 electrons in s and 1 electron each in 2px and 2pz orbitals.

According to Hund’s rule, each orbital in a shell or subshell must be first occupied by 1 electron before being occupied with 2. In simple words, all the orbitals must first be filled with 1 electron before any orbital is filled with 2 electrons.

Hund’s rule states — the ground state of an atom or the state with the lowest energy electron configuration is the state with the highest number of parallel electron spins.

Following Hund’s rule, 1 electron from 2s goes to the 2pz

This is the lowest electron energy configuration of the carbon atom, the ground state.

The hybridization state of CH3OH is sp3.

Sp3 hybridization should form a tetrahedral shape, but in this case, the shape varies.

Let’s figure out why that is.

CH3OH Shape

CH3OH has two geometric centers, one is the carbon atom and the other is oxygen.

CH3OH has sp3 hybridization, therefore it should depict a tetrahedral shape.

But CH3OH depicts both tetrahedral and bent tetrahedral shape instead of tetrahedral throughout.

There is one reason for that — the presence of lone pairs on the Oxygen atom.

These two lone pairs on the O atom cause repulsion within the CH3OH molecule. Thus instead of tetrahedral, CH3OH forms also forms a bent shape.

Around the Carbon atom, it shows a tetrahedral geometry with 3 hydrogen bonds and 1 hydroxyl bond.

On the other hand, around the O atom, it shows a bent tetrahedral geometry with 1 carbon bond, 1 hydrogen bond, and 2 lone pairs.

Conclusion

CH3OH is an easier structure for you to understand. You must start working simply before you go for further complex compounds.

You can clear your concepts on Lewis structure, hybridization, and molecular geometry by practicing it on paper. Scroll back up. Read it again, and again.

As an exercise, try drawing the Lewis structure of CH3OH yourself. Try to find out the hybridization state without referencing. Try to reason why the molecular geometry of CH3OH has 2 geometric centers!