Geometry, Hybridization, and Polarity of CH3OH Lewis Structure

Methanol, commonly known as methyl alcohol, has the chemical formula CH3OH, which is the simplest aliphatic alcohol. It’s a primary alkyl alcohol with a methyl group and a hydroxyl functional group attached.

Due to the presence of a hydroxyl functional group, it is a polar solvent. It has a molecular mass of 32.042g, is colourless, and has a pungent odour. It is also volatile.

To learn more about methanol, you need first learn about its bonding properties.

For this, a thorough understanding of the Lewis structure, VSEPR theory, the Hybridization notion, and its polar nature is essential.

Lewis Structure of CH3OH

The simplest representation of valence shell electrons around a molecule is the Lewis Structure.

Because a single bond consists of two bonding electrons, the two dots between two atoms are represented by a line instead, which depicts a bond between them.

A lewis structure tells us if there is a binding between atoms, but it doesn’t tell us what type of bond it is.

It is necessary to first satisfy the octet rule before calculating the formal charge of each element in the molecule in order to construct the Lewis structure of methanol.

The octet rule specifies that every element must have a noble gas configuration, which means that its valence shells must have a total of 2 electrons (in the case of H and He) or a total of 8 electrons. This is due to the fact that noble gases are considered stable in nature.

A formal charge is a theoretical charge that exists on molecular elements. The net charge on the molecule must be equal to the total of these formal charges. The following formula is used to compute it:

(Valence electrons) – (bonding electrons)/2) – Formal charge of an element (Non bonding electrons)

Drawing the Lewis Structure of Methanol in Steps (CH3OH)

1) Total valence electrons in methanol calculation

The total number of valence electrons in a molecule is equal to the sum of each element’s valence shell electrons.

Take a look at the table below for further information.

AtomAtomic numberGroup NumberElectronic configurationValence shell electronic configurationNo. of valence electrons
C6141s22s22p22s22p24
O8161s22s22p42s22p46
H111s11s11

One CH3OH molecule now has one carbon atom, one oxygen atom, and four hydrogen atoms. As a result, the total valence electrons are as follows:

14 valence shell electrons (14) + (16) + (1*4)

2) Making a rudimentary diagram

The core atom of the molecule must be chosen in order to construct a preliminary picture.

The core atom should not be extremely electronegative or too tiny in size. As a result, both C and O are suitable central atoms in methanol.

The Lewis structure of methanol, on the other hand, can be simply depicted by using either of the elements as the centre atom.

We’ll take a step forward here by using carbon as the core atom. Methanol has three C-H bonds, one C-O bond, and one O-H bond, as can be shown.

The rough sketch resembles the illustration below.

3) Allocating valence electrons to certain atoms

The placement of valence electrons around the individual atoms is depicted in the diagram below.

4) Comply with each atom’s octet rule and draw the final Lewis structure.

Because methanol has a total of 14 valence shell electrons, there must be 7 electron pairs in the molecule.

Two bonding electrons form a bond, which is depicted by a line, as we all know.

The Lewis structure is shown here, with all bonds and lone pairs visible, as well as the satisfied octet rule.

Calculating the formal charge is the final step in completing the Lewis diagram. As we previously discussed, the formal charge can be calculated using the following formula:

(Valence electrons) – (bonding electrons)/2) – Formal charge of an element (Non bonding electrons)

Where;

The electrons involved in bond formation are known as bonding electrons.

Non-bonding electrons are lone pairs of electrons that do not form bonds surrounding each atom.

AtomValence electronsBonding electronsNon-bonding electronsFormal charge
C4800
O6440
H1200

The sum of the formal charges on each atomic atom is the net charge on a molecule. As a result, the methanol molecule’s net charge is;

(1*0)C + (1*0)O + (4*0)H = 0

This means that methanol is a neutral molecule with two lone pairs on the oxygen atom, and its ultimate Lewis structure will resemble the one shown in the graphic below.

Although it is difficult to discern a compound’s geometry and hybridization exactly using this notion, it is acceptable that a Lewis structure provides a lot of information about it.

As a result, familiarity with the VSEPR theory and hybridization notion is required.

Molecular Geometry of CH3OH

The Valence Shell Electron Pair Repulsion (VSEPR) Theory, which is based on the concept that a molecule stabilises itself in a certain form in which it encounters the least amount of electron-electron repulsions, can explain the molecular geometry of a compound very well.

If the difference between the number of bond pairs electrons and the steric number is not zero, the molecule’s molecular shape is not the same as its molecular geometry, i.e. the molecule contains non-zero lone pairs.

According to the VSEPR theory, each type of geometry is allocated a steric number, which may be computed using the following formula:

(X + M + |a| – b)/2 = Steric number (S)

Where;

X denotes the number of valence electrons in the centre atom.

M denotes the number of monoatomic side atoms.

a = molecule’s negative charge

b = molecule’s positive charge

The steric number allocated to each shape is listed in the table below.

According to the VSEPR theory, the steric number of CH3OH is computed as follows:

1) Using Carbon as the core atom, calculate the steric number of methanol.

The number of valence electrons in a carbon atom is equal to four.

The number of monoatomic side atoms is equal to four.

Because methanol is neutral, as shown by the formal charge calculation, the values of a and b are 0.

CH3OH steric number in relation to C = (4 + 4) / 2 = 4

Because the methanol molecule has a steric number of 4, it has a tetrahedral shape with respect to the carbon atom.

2) Using oxygen as the core atom, calculate the steric number of methanol.

The oxygen atom has six valence electrons.

The number of monoatomic side atoms is equal to two.

Because methanol is neutral, as shown by the formal charge calculation, the values of a and b are 0.

CH3OH steric number in relation to O = (6 + 2) / 2 = 4

Because the methanol molecule has a steric number of 4, it also possesses tetrahedral geometry with respect to the oxygen atom.

Molecular Structure of CH3OH

Depending on the number of lone pairs in the molecule, a compound with tetrahedral geometry can have four different molecular forms.

The presence of lone pair-lone pair repulsions, lone pair-bond pair repulsions, and bond pair-bond pair repulsions in a molecule causes the varied shapes in a given type of geometry.

Subtracting the number of bond pairs from the steric number yields the number of lone pairs in a compound.

A compound with three bond pairs and one lone pair will have a pyramidal form.

When a compound has two bond pairs and two lone pairs, it takes on a bent or linear shape.

Tetrahedral geometry is defined as a composite with four bond pairs and no lone pairs.

In the case of methanol, for example;

Because the core carbon atom contains four sigma bonds and no lone pairs, methanol has a tetrahedral form with equal bond angles of 109.5 degrees with respect to the carbon atom.

Because the oxygen atom has two sigma bonds and two lone pairs, methanol has a bent shape and a bond angle of 104.5 degrees with the oxygen atom.

Hybridization of CH3OH

Hybridization is a term used to describe the production of hybrid orbitals when pure atomic orbitals with identical energy and shape are mixed.

It is, however, required that the number of hybrid orbitals created be equal to the number of atomic orbitals mixed together.

The concept of hybridization aids in explaining bonding in complicated geometrical structures.

Hybridization, for example, can be readily or directly determined using the compound’s steric number.

The hybridization of each steric number value is shown in the table below.

We can tell that the hybridization of methanol is sp3 in terms of both carbon and oxygen as central atoms by looking at the table, because both of them make the steric number of the molecule equal to 4.

The detailed procedure for calculating a compound’s hybridization, on the other hand, is as follows:

In the ground state, C’s electrical arrangement is 1s2 2s2 2p2, which is written as

follows:

Carbon will need to extend its octet by exciting one of its valence electrons in the 2s orbital to the 2p orbital in order to join with three hydrogen atoms and one hydroxyl group.

In an excited state, carbon’s electrical arrangement is now 1s2 2s1 2p3, which is written as

follows:

The four atomic orbitals, one 2s and three 2p orbitals, combine to generate four sp3 hybrid orbitals, as shown in the diagram below.

As a result, we can state that CH3OH hybridization is sp3.

In addition, I’ve written an article about ethanol. Take a look at ethanol’s hybridization, geometry, and Lewis structure.

Polarity of CH3OH

The link between two atoms is considered to be polar if their charge distributions are uneven or if there is an electronegativity difference between them.

The dipole moment, which is the magnitude of the product of the partial charge of atoms and the distance between them, is another factor that influences the polarity of a compound.

If the dipole moment () is greater than zero, a compound is said to be polar.

There must be an electronegativity difference between two atoms for a dipole moment to exist between them.

Methanol has three C-H bonds, one C-O bond, and one O-H bond, as we know.

As a result, the electronegativity difference between a C-H, a C-O, and an O-H bond must be calculated.

C has an electronegativity of 2.55, O has a value of 3.44, and H has a value of 2.2.

The difference in electronegativity in the C-H bond is 2.55 – 2.2 = 0.35, which is almost insignificant. As a result, the C-H bond is a nonpolar one.

The C-O bond has an electronegativity difference of 3.44 – 2.55 = 0.89, which cannot be ignored. As a result, the C-O bond is polar.

The O-H bond has an electronegativity difference of 3.44 – 2.2 = 1.24, making it polar.

Looking at the image again, we can see that both arrows indicating the direction of the dipole moment are pointing towards the oxygen atom.

Because oxygen is more electronegative than carbon or hydrogen (as seen by electronegativity values), the electron density of the bond is moved further towards oxygen, and the two dipole moments do not cancel out.

You should look at the polarity of CH3OH for further information.

Methanol is therefore a polar molecule.

Methanol, on the other hand, is a well-known polar solvent that is employed in a wide range of chemical processes.

The presence of the hydroxyl functional group causes hydrogen bonding in the molecule, which causes this.

When methanol is dissolved in water, the hydroxyl group initiates hydrogen bonding between the methanol molecule and the water molecules.

This makes the chemical water soluble.

Conclusion

To summarise, CH3OH is a polar and neutral molecule with a tetrahedral geometry and bent and tetrahedral forms in relation to the oxygen and carbon atoms.

Along with the hybridization of sp3, it has three C-H sigma nonpolar bonds, one C-O sigma polar bond, and one O-H sigma polar bond.

Read more: Is CH2Br2 a polar or a nonpolar compound?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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