Worked examples: Finding the hybridization of atoms in organic molecules | Khan Academy

Summary

This educational video script explores the concept of hybridization in organic chemistry, providing step-by-step examples to identify hybridization states and predict molecular geometries for various atoms, excluding hydrogen. It explains the process of determining hybridization through steric numbers and sigma/pie bond counts, illustrating the geometries such as trigonal planar, tetrahedral, linear, and trigonal pyramidal. The script also emphasizes the importance of symmetry in simplifying the analysis of molecules like diethyl ether.

Takeaways

• 🧬 The script discusses the concept of hybridization and its importance in understanding molecular geometry.
• 🔍 To identify hybridization, one can look at the type of bonds (single, double, triple) associated with an atom.
• 📊 SP2 hybridization is associated with a trigonal planar geometry and bond angles of approximately 120 degrees.
• 📐 SP3 hybridization results in a tetrahedral geometry with ideal bond angles of 109.5 degrees.
• 🔬 SP hybridization leads to a linear geometry with a bond angle of 180 degrees.
• 📝 The total number of sigma and pi bonds in a molecule can be counted to further understand its structure.
• 🌈 Sigma bonds are represented in blue, while pi bonds are in red in the script's illustrations.
• 🔢 The steric number, calculated as the sum of sigma bonds and lone pairs, helps determine the hybridization state of an atom.
• 🌀 Hydrogen atoms are excluded from hybridization analysis as they are only bonded to one other atom and do not have a significant geometry.
• 🧩 In the example of diethyl ether, all carbon atoms are SP3 hybridized with a tetrahedral geometry, while the oxygen is SP3 hybridized but has a bent geometry due to lone pairs.
• 🌟 The script emphasizes the importance of symmetry in simplifying the analysis of molecular geometry, as seen in the diethyl ether example.

Q & A

What is the primary method discussed in the script for identifying the hybridization state of carbon atoms?

The primary method discussed is to look at the type of bonds a carbon atom has. For example, if a carbon has a double bond, it is SP2 hybridized; if it has a triple bond, it is SP hybridized; and if it only has single bonds, it is SP3 hybridized.

What is the geometrical shape associated with SP2 hybridization?

The geometrical shape associated with SP2 hybridization is trigonal planar, with bond angles approximately 120 degrees.

How many sigma and pi bonds are there in a double bond?

A double bond consists of one sigma bond and one pi bond.

What is the hybridization state of a carbon atom with only single bonds around it?

A carbon atom with only single bonds around it is SP3 hybridized.

What is the ideal bond angle in a tetrahedral geometry?

The ideal bond angle in a tetrahedral geometry is 109.5 degrees.

What is the hybridization state of a carbon atom with a triple bond?

A carbon atom with a triple bond is SP hybridized.

What is the geometrical shape associated with SP hybridization?

The geometrical shape associated with SP hybridization is linear, with a bond angle of 180 degrees.

How many sigma bonds are there in the molecule discussed in the script?

There are a total of 10 sigma bonds in the molecule discussed in the script.

How many pi bonds are there in the molecule discussed in the script?

There are three pi bonds in the molecule discussed in the script.

What is the steric number and how is it used to determine hybridization states?

The steric number is the sum of the number of sigma bonds and lone pairs of electrons around an atom. It is used to determine the hybridization state by indicating the number of hybrid orbitals needed to accommodate the electron groups.

Why are hydrogen atoms excluded from the hybridization and geometry analysis in the script?

Hydrogen atoms are excluded because they are only bonded to one other atom and do not have a geometry that can be analyzed in the same way as other atoms with multiple bonds or lone pairs.

What is the hybridization state of the oxygen atom in diethyl ether, and what is its geometry?

The oxygen atom in diethyl ether is SP3 hybridized, and its geometry is bent or angular, not tetrahedral, due to the presence of two lone pairs of electrons.

What is the difference between the electron group geometry and the molecular geometry around an SP3 hybridized atom?

The electron group geometry refers to the arrangement of all electron groups (including lone pairs) around an atom, which for SP3 hybridization would be tetrahedral. However, the molecular geometry only considers the positions of the atoms bonded to the central atom, which can be different from the electron group geometry due to the presence of lone pairs.

What is the hybridization state and geometry of the nitrogen atom in the last example of the script?

The nitrogen atom in the last example is SP3 hybridized, but its geometry is trigonal pyramidal due to the presence of three sigma bonds and one lone pair of electrons.

Outlines

00:00

🔬 Understanding Molecular Geometry and Hybridization

This paragraph introduces the concept of hybridization states and their role in predicting molecular geometries. It focuses on a molecule where carbon atoms with double bonds are identified as sp2 hybridized, resulting in trigonal planar geometry with bond angles of 120 degrees. Single-bonded carbons are considered sp3 hybridized, leading to tetrahedral geometry with bond angles of 109.5 degrees. Carbons with triple bonds are sp hybridized, resulting in linear geometry at 180 degrees. The paragraph also explains the process of counting sigma and pi bonds within the molecule and uses the steric number concept to determine hybridization states, excluding hydrogen due to its lack of geometry.

05:02

🧪 Analyzing Diethyl Ether's Hybridization and Geometry

The second paragraph delves into the analysis of diethyl ether, starting with the carbon atoms, which are sp3 hybridized due to their tetrahedral geometry with only single bonds present. The oxygen atom's hybridization is determined using the steric number, which accounts for sigma bonds and lone pairs, leading to sp3 hybridization with four hybrid orbitals. However, despite being sp3 hybridized, the geometry around the oxygen is bent or angular due to the presence of lone pairs, which are not considered when determining the shape of the molecule. The paragraph emphasizes the use of symmetry to simplify the analysis of the molecule's hybridization states.

10:05

📚 Continuing Organic Hybridization Examples

The final paragraph continues the exploration of hybridization with another example, emphasizing the importance of practice. It reiterates the method of identifying hybridization states by observing the types of bonds present around atoms, such as sp2 for double bonds leading to trigonal planar geometry, and sp3 for single bonds resulting in tetrahedral geometry. The paragraph also discusses nitrogen's hybridization, which is sp3, but its geometry is trigonal pyramidal due to the presence of a lone pair of electrons. The summary reinforces the concepts introduced in the previous paragraphs and encourages further study of the topic.

Keywords

💡Hybridization

Hybridization in chemistry refers to the concept where atomic orbitals combine to form new hybrid orbitals that are suitable for bonding. In the context of the video, hybridization is essential for understanding the geometry around atoms in organic molecules. For example, the script mentions 'SP' hybridization, which is a type of hybridization where one s and one p orbital combine to form two sp hybrid orbitals, resulting in a linear geometry.

💡Steric Number

The steric number is a term used to predict the shape of a molecule and is calculated by adding the number of atoms bonded to a central atom plus the number of lone pairs on that atom. It is crucial in the video for determining the hybridization state of atoms. For instance, a steric number of four indicates SP3 hybridization, which is associated with a tetrahedral geometry, as discussed in the video with the oxygen atom in diethyl ether.

💡Geometry

Geometry in the context of chemistry refers to the spatial arrangement of atoms around a central atom in a molecule. The video script explains how different hybridization states lead to distinct geometries. For example, 'trigonal planar' geometry is associated with SP2 hybridization, and 'tetrahedral' geometry is associated with SP3 hybridization, both of which are illustrated with carbon atoms in various molecules.

💡Sigma Bonds

Sigma bonds are the strongest type of covalent bond formed by the head-on overlapping of atomic orbitals. The script emphasizes counting sigma bonds to determine the hybridization state and overall molecular geometry. For example, every double bond contains one sigma bond, and every single bond is a sigma bond, as illustrated when analyzing the carbon atoms in the molecules.

💡Pi Bonds

Pi bonds are a type of covalent bond that results from the side-by-side overlap of p orbitals, above and below the plane of the sigma bond. The video script mentions pi bonds in the context of double and triple bonds, where a double bond consists of one sigma and one pi bond, and a triple bond consists of one sigma and two pi bonds, as demonstrated when discussing the bonds around carbon and nitrogen atoms.

💡Trigonal Planar

Trigonal planar is a molecular geometry where there are three bonds around a central atom with bond angles of approximately 120 degrees. In the video, this geometry is associated with SP2 hybridization, as seen with carbon atoms involved in double bonds, which have three regions of electron density (two bonds and no lone pairs) resulting in a planar arrangement.

💡Tetrahedral

Tetrahedral geometry describes a molecule where four bonds are arranged symmetrically around a central atom with bond angles of approximately 109.5 degrees. The script uses this term to describe the geometry around carbon atoms with SP3 hybridization, which occurs when there are four regions of electron density (four single bonds and no lone pairs).

💡Linear

Linear geometry is a molecular shape where all atoms are aligned in a straight line, with a bond angle of 180 degrees. The video script explains that atoms with SP hybridization, such as those involved in triple bonds, exhibit linear geometry. This is exemplified by carbon atoms bonded to nitrogen with a triple bond, resulting in a straight line formation.

💡Lone Pairs

Lone pairs are pairs of electrons that are not involved in bonding and are found in the valence shell of an atom. The video script discusses the importance of considering lone pairs when calculating the steric number, which influences the hybridization and geometry of atoms. For example, the oxygen in diethyl ether has two lone pairs, contributing to its steric number and hybridization state.

💡Diethyl Ether

Diethyl ether is a specific organic compound used as an example in the video script to illustrate the concepts of hybridization and geometry. It contains an oxygen atom bonded to two ethyl groups, and the analysis of its structure helps to explain the concept of steric number and the bent or angular geometry around the oxygen atom due to the presence of lone pairs.

💡Trigonal Pyramidal

Trigonal pyramidal is a molecular geometry where a central atom is bonded to three other atoms and has one lone pair of electrons, resulting in a three-dimensional shape that is not symmetrical. The video script describes the geometry around a nitrogen atom in a molecule, where the steric number is four (three sigma bonds and one lone pair), leading to an SP3 hybridization but a trigonal pyramidal shape due to the influence of the lone pair.

Highlights

Understanding hybridization states is crucial for predicting molecular geometries.

A carbon atom with a double bond is SP2 hybridized, leading to a trigonal planar geometry with bond angles of 120 degrees.

An SP2 hybridized carbon with a double bond has a trigonal planar geometry, regardless of its position in the molecule.

Carbon atoms with only single bonds are SP3 hybridized, resulting in a tetrahedral geometry with bond angles of 109.5 degrees.

A carbon atom with a triple bond is SP hybridized, adopting a linear geometry with a bond angle of 180 degrees.

Counting sigma and pi bonds is essential for understanding molecular structure.

Sigma bonds are represented in blue, while pi bonds are in red for clear distinction.

The total number of sigma bonds in the molecule is 10, and pi bonds is 3.

Hybridization states can also be determined using the steric number, calculated as the sum of sigma bonds and lone pairs.

A steric number of three corresponds to SP2 hybridization, while four corresponds to SP3 hybridization.

Hydrogen atoms are excluded from hybridization analysis as they are only bonded to one other atom and do not contribute to molecular geometry.

Diethyl ether serves as an example to illustrate the application of hybridization and geometry concepts.

Oxygen in diethyl ether with two sigma bonds and two lone pairs has a steric number of four, indicating SP3 hybridization.

Despite being SP3 hybridized, the geometry around oxygen in diethyl ether is bent due to the presence of lone pairs.

Symmetry in molecules simplifies the analysis of hybridization and geometry, as seen in the carbon atoms of diethyl ether.

In another example, a carbon with a double bond is SP2 hybridized with a trigonal planar geometry.

A nitrogen atom with three sigma bonds and one lone pair has a steric number of four, indicating SP3 hybridization.

The geometry around a nitrogen atom is trigonal pyramidal, not tetrahedral, due to the presence of a lone pair.

Practice is key to mastering the concepts of organic hybridization and molecular geometry.

Transcripts

Voiceover: Now that we understand hybridization

states, let's do a couple of examples,

and so we're going to identify the hybridization

states, and predict the geometetries

for all the atoms in this molecule, except

for hydrogen, and so, let's start

with this carbon, right here.

And so, the fast way of identifying a hybridization

state, is to say, "Okay, that carbon has

"a double bond to it; therefore, it must

"be SP two hybridized."

And if it's SP two hybridized, we know

the geometry around that carbon must be trigonal,

planar, with bond angles approximately 120 degrees.

This carbon over here, also has a double-bond

to it, so it's also SP two hybridized,

with trigonal planar geometry.

All right, let's move to this carbon, right here,

so that carbon has only single bonds around it,

and the fast way of doing it, is if you see

all single bonds, it must be SP three hybridized,

and if that carbon is SP three hybridized,

we know the geometry is tetrahedral,

so tetrahedral geometry with ideal bond angles

of 109 point five degrees around that carbon.

All right, let's move over to this carbon,

right here, so this carbon has a triple-bond

on the right side of it, and so the fast way

of doing this, is if it has a triple-bond,

it must be SP hybridized here, so SP hybridized,

and therefore, the geometry would be linear,

with a bond angle of 180 degrees.

And, same with this carbon; this carbon has

a triple-bond to it, so it also must be

SP hybridized with linear geometry, and so

that's why I drew it this way, so it's linear

around those two carbons, here.

Let's go ahead and count up the total number

of sigma and pi bonds for this, so that's

also something we talked about

in the previous videos here.

So, first let's count up the number of sigma bonds,

so let's go back over to start with this carbon, here.

So here's a sigma bond to that carbon,

here's a sigma bond to that carbon; we know that

our double-bond, one of those bonds is a sigma bond,

and one of those bonds is a pi bond,

so let me go ahead,

and also draw in our pi bonds, in red.

So, already colored the sigma bond blue, and so

let's say this one is the pi bond.

All right, let's continue assigning all of our bonds here.

So I know this single-bond is a sigma bond,

I know this single-bond is a sigma bond,

so all of these single bonds here are sigma.

When I get to the triple bond, I know one of those

is a sigma bond, and two of those are pi bonds.

So, two of those are pi bonds, here.

And then, finally, I have one more bond; it's a single-bond,

so I know that it is a sigma bond here,

and if you count up all of those sigma bonds,

you should get 10, so let's do that really quickly.

So you get, let me go ahead and change colors here,

so you get one, two, three, four, five, six,

seven, eight, nine, and 10; so we have 10

sigma bonds total, and in terms of pi bonds,

we had three pi bonds, so three pi bonds

for this molecule.

You can also find hybridization states

using a steric number, so let's go ahead

and do that really quickly.

So let's go back to this carbon, and let's find

the hybridization state of that carbon,

using steric number.

So let's use green for this, so steric number

is equal to the number of sigma bonds,

plus lone pairs of electrons.

So, one, two, three sigma bonds around that carbon.

So three plus zero gives me a steric number of three,

therefore I need three hybrid orbitals,

and SP two hybridization gives me three hybrid orbitals.

All right, if I wanted to do for this carbon

I would have one, two, three four; so the steric number

would be equal to four sigma bonds, and zero lone pairs

of electrons, giving me a total of four

for my steric numbers, so I need four hybrid orbitals;

I have four SP three hybridized orbitals at that carbon.

And then finally, let's do it for this carbon,

right here, so using steric number.

Steric number is equal to number of sigma bonds,

plus numbers of lone pairs of electrons,

so there are two sigma bonds around that carbon,

zero lone pairs of electrons, steric number of two,

means I need two hybridized orbitals,

and an SP hybridization, that's what you get:

You get two SP hybridized orbitals, like that.

All right, let's move onto another example;

let's do a similar analysis.

Before we do, notice I excluded hydrogen here,

and that's because hydrogen is only bonded

to one other atom, so there's no real geometry

to talk about.

All right, let's move on to this example.

So this molecule is diethyl ether, and let's start

with this carbon, right here, so the hybridization state.

Well, the fast way of doing it, is to notice

that there are only single-bonds around that carbon,

only sigma bonds, and so, therefore we know

that carbon is SP three hybridized,

with tetrahedral geometry, so SP three hybridized,

tetrahedral geometry.

All right, let's look at this carbon right here;

it's the exact same situation, right,

only sigma, or single bonds around it,

so this carbon is also SP three hybridized,

and so, therefore tetrahedral geometry.

Let's next look at the oxygen here, so if I wanted

to figure out the hybridization and the geometry

of this oxygen, steric number is useful here,

so let's go ahead and calculate

the steric number of this oxygen.

So that's number of sigma bonds, so here's

a single-bond, so that's a sigma bond,

and then here's another one; so I have two

sigma bonds, so two plus number of lone pairs

of electrons around the atom, so here's a lone pair

of electrons, and here's a lone pair of electrons.

So, I have two lone pairs of electrons,

so two plus two gives me a steric number of four,

so I need four hybridized orbitals for this oxygen,

and we know that occurs when you have

SP three hybridization, so therefore,

this oxygen is SP three hybridized:

There are four SP three hybrid orbitals around that oxygen.

All right, let's do geometry of this oxygen.

So, the electron groups, there are four electron groups

around that oxygen, so each electron group

is in an SP three hydbridized orbital.

The geometry of those electron groups

might be tetrahedral, but not the geometry

around the oxygen here, so the geometry around the oxygen,

if you ignore the lone pairs of electrons,

you can see that it is bent, so even though

that oxygen is SP three hybridized, it's geometry

is not tetrahedral; the geometry

of that oxygen there is bent or angual.

All right, and because of symmetry, this carbon

right here is the same as this carbon, so it's also

SP three hybridized, and then this carbon over here

is the same as this carbon,

so it's also SP three hybridized,

so symmetry made our lives easy on this one.

All right, let's do one more example.

So, once again, our goal is to find the hybridization

states, and the geometries for all the atoms,

except for hydrogen, and so, once again,

let's start with carbon; let's start

with this carbon, right here.

All right, so once again, our goal is to find

the hybridization state, so the fast way of doing it,

is to notice there's one double-bond to that carbon,

so it must be SP two hybridized, and therefore

the geometry is trigonal planar,

so trigonal planar geometry.

Let's do the steric number way, so if I were

to calculate the steric number:

Steric number is equal to the number of sigma bonds.

So here's a sigma bond, here's a sigma bond;

I have a double-bond between the carbon and the oxygen,

so one of those is a sigma bond,

and one of those is a pi bond, which I'll draw in red here.

So I have three sigma bonds around that carbon,

so three plus zero lone pairs of electrons,

gives me a steric number of three, so I need

three hybridized orbitals, and so once again,

SP two hybridization.

All right, let's do the next carbon,

so let's move on to this one.

So, I see only single-bonds around that carbon,

therefore, it must be SP three hybridized,

with tetrahedral geometry, so SP three hybridized,

tetrahedral geometry.

Same thing for this carbon, only single-bonds around it,

only sigma bonds, so it's SP three hybridized,

with tetrahedral geometry.

Let's finally look at this nitrogen here.

So if I want to find the hybridization state of this nitrogen,

I could use steric number.

So the steric number is equal to number of sigma bonds.

So around this nitrogen,

here's a sigma bond; it's a single bond.

Here's another one, and here's another one,

so I have three sigma bonds.

I have one lone pair of electrons,

so three plus one gives me four, a steric number of four,

means I need four hybridized orbitals,

and that's our situation with SP three hybridization.

And so, this nitrogen is SP three hybridized,

but it's geometry is not tetrahedral, so the

geometry for that nitrogen, as we discussed

in an earlier video, so it has these three

sigma bonds like this, and a lone pair

of electrons, and that lone pair of electrons

is in an SP three hybridized orbital.

And if we look at that geometry, and ignore

the lone pair of electrons, 'cause you always

ignore the lone pairs of electrons, when you're

looking at geometry, we can see, we have

this sort of shape here, so the nitrogen's

bonded to three atoms: the carbon, hydrogen,

and hydrogen, and then we have this sort

of a shape, like that, so in the back there,

and you can see, we call this trigonal-pyramidal,

so the geometry around that nitrogen is trigonal pyramidal.

All right, so that does it for three examples

of organic hybridization, so practice a lot for this.