Polar and Nonpolar Molecules

Summary

This video script delves into the distinction between polar and nonpolar molecules. It begins by explaining what it means for a molecule to be polarized, using four objects to illustrate the concept. The script then uses hydrofluoric acid (HF) as an example of a polar molecule due to the unequal sharing of electrons between hydrogen and fluorine, leading to a partial negative charge on fluorine and a partial positive charge on hydrogen. The difference between polar and nonpolar molecules is clarified by the sharing of electrons; polar molecules have an unequal sharing, whereas nonpolar molecules share electrons more equally. The script outlines rules for identifying nonpolar molecules, such as those containing only one type of element or hydrocarbons. The importance of molecular geometry in determining polarity is emphasized, with examples like carbon tetrafluoride (nonpolar due to dipole moment cancellation) and water (polar due to a net dipole moment). The video concludes with a step-by-step guide to determine if a molecule is polar or nonpolar, including examining electronegativity differences, molecular geometry, and the presence of a net dipole moment.

Takeaways

• 🔬 To determine if a molecule is polar or nonpolar, one must consider both the electronegativity difference between atoms and the molecular geometry.
• ⚖️ A molecule is considered polar if it has a net dipole moment, meaning the individual bond dipoles do not cancel each other out.
• 🔋 Polar molecules have an unequal sharing of electrons, resulting in a partial positive charge on one side and a partial negative charge on the other.
• ❌ Nonpolar molecules have a relatively equal sharing of electrons, leading to an overall neutral charge distribution.
• 🏷️ Molecules containing only one type of element, like H2 or O2, are automatically nonpolar due to the lack of difference in electronegativity.
• 🚫 Hydrocarbons, which are molecules containing only carbon and hydrogen, are nonpolar because the electronegativity difference between carbon and hydrogen is less than 0.5.
• 📐 The geometry of a molecule plays a crucial role in its polarity; for instance, a tetrahedral shape in carbon tetrafluoride leads to a cancellation of dipole moments, making it nonpolar.
• 🎯 In contrast, water (H2O) has a bent shape that does not allow for the cancellation of its dipole moments, resulting in a polar molecule.
• 🔄 The dipole moment is represented as an arrow pointing from the atom with a partial positive charge towards the atom with a partial negative charge.
• 🧲 Electronegativity values are key in determining the polarity of bonds within a molecule; a difference of 0.5 or more typically indicates a polar bond.
• 📚 Understanding the concepts of electronegativity, molecular geometry, and dipole moments is essential for quickly identifying whether a molecule is polar or nonpolar.

Q & A

What is the primary characteristic of a polar molecule?

A polar molecule has a separation of charge, where one part of the molecule has a partial positive charge and the other part has a partial negative charge.

How does electronegativity play a role in determining if a bond is polar or nonpolar?

The difference in electronegativity between two elements in a bond determines its polarity. If the electronegativity difference is greater than or equal to 0.5, the bond is considered polar.

Why is hydrofluoric acid (HF) considered a polar molecule?

Hydrofluoric acid is polar because fluorine is more electronegative than hydrogen, causing an unequal sharing of electrons and resulting in a partial negative charge on fluorine and a partial positive charge on hydrogen.

What is the significance of molecular geometry in determining the polarity of a molecule?

Molecular geometry can affect the overall polarity of a molecule by influencing how the individual bond dipoles are oriented in space. If the bond dipoles cancel each other out, the molecule is nonpolar; if they do not, the molecule is polar.

How does the electronegativity difference between carbon and hydrogen affect the polarity of hydrocarbons?

The electronegativity difference between carbon and hydrogen is 0.4, which is less than 0.5. This makes the carbon-hydrogen bond nonpolar, and thus hydrocarbons, which contain only carbon and hydrogen, are nonpolar molecules.

What is a dipole moment and how is it related to the polarity of a molecule?

A dipole moment is a measure of the separation of positive and negative charges in a molecule, represented by an arrow pointing from the partial positive charge towards the partial negative charge. If the sum of all dipole moments in a molecule is not zero, the molecule is polar.

Why is carbon dioxide (CO2) considered a nonpolar molecule despite having polar bonds?

Carbon dioxide is nonpolar because its linear molecular geometry causes the dipole moments of the polar bonds to cancel each other out, resulting in an overall dipole moment of zero.

What is the electronegativity difference between carbon and fluorine that makes the carbon-fluorine bond in carbon tetrafluoride (CF4) polar?

The electronegativity difference between carbon and fluorine is 1.5, which is greater than 0.5, making the carbon-fluorine bond in CF4 polar.

How does the molecular geometry of water (H2O) contribute to its polarity?

The molecular geometry of water is bent, which does not allow the dipole moments to cancel each other out. This results in a net dipole moment, making water a polar molecule.

What is the role of lone pairs of electrons in determining the polarity of a molecule like water?

Lone pairs of electrons contribute to the molecule's polarity by creating regions of higher electron density, which can lead to a partial negative charge. In water, the lone pairs on the oxygen atom, combined with the bent geometry, result in a net dipole moment.

How can you quickly determine if a molecule is polar or nonpolar during a test?

You can quickly determine the polarity of a molecule by first checking if it contains only one type of element or if it's a hydrocarbon. If not, draw the Lewis structure, analyze the bond polarities, and consider the molecular geometry to see if the dipole moments cancel out or result in a net dipole moment.

Outlines

00:00

🔬 Understanding Molecular Polarity

The video begins by introducing the concept of molecular polarity and nonpolarity. It explains that a polarized object has distinct positive and negative charges. The video uses hydrofluoric acid (HF) as an example of a polar molecule due to the electronegativity difference between hydrogen and fluorine, which leads to a partial negative charge on fluorine and a partial positive charge on hydrogen. In contrast, nonpolar molecules like hydrogen gas (H2) share electrons equally, resulting in no separation of charge. The video also provides rules to quickly determine if a molecule is polar or nonpolar, such as molecules containing only one type of element being nonpolar and hydrocarbons being nonpolar due to the small electronegativity difference between carbon and hydrogen.

05:03

🌐 Molecular Geometry and Polarity

The video continues by emphasizing the importance of molecular geometry in determining polarity. It explains that even though individual bonds in a molecule can be polar, the overall molecule can be nonpolar if the molecular geometry causes the bond dipoles to cancel out. Using carbon tetrafluoride as an example, the video shows that despite the polar C-F bonds, the tetrahedral geometry leads to a net dipole moment of zero, making the molecule nonpolar. The video also discusses water (H2O), which has polar O-H bonds and a bent molecular geometry that results in a net dipole moment, confirming its polarity. The concept of vector addition is introduced to explain why the dipole moments in water do not cancel out, leading to a polar molecule.

10:04

📐 Determining Polarity with Lewis Structures

The final part of the video focuses on using Lewis structures to determine the polarity of molecules. It contrasts carbon dioxide (CO2) and sulfur dioxide (SO2) to illustrate this point. Both CO2 and SO2 have polar C-O and S-O bonds, respectively, due to the electronegativity difference between carbon/sulfur and oxygen. However, the linear geometry of CO2 leads to dipole moments that cancel each other out, resulting in a nonpolar molecule. In contrast, the bent shape of SO2 causes the dipole moments to add up, resulting in a net dipole moment and a polar molecule. The video concludes by summarizing the steps to determine if a molecule is polar or nonpolar: checking for single-element molecules or hydrocarbons, analyzing the electronegativity difference, and considering the molecular geometry and the resulting dipole moments.

Keywords

💡Polar Molecule

A polar molecule is one in which there is an unequal sharing of electrons between atoms, resulting in a separation of charge, with one part of the molecule having a partial positive charge and another part having a partial negative charge. This concept is central to the video's theme, as it helps in distinguishing between polar and nonpolar molecules. For example, hydrofluoric acid (HF) is highlighted as a polar molecule due to the electronegativity difference between hydrogen and fluorine, causing a dipole with a partial negative charge on fluorine and a partial positive charge on hydrogen.

💡Nonpolar Molecule

A nonpolar molecule is characterized by an equal sharing of electrons between atoms, leading to no separation of charge and an overall neutral charge distribution. This term is crucial in the video as it represents the opposite of a polar molecule. Hydrogen gas (H2) is used as an example of a nonpolar molecule because it consists of two identical atoms sharing electrons equally, resulting in no regions of positive or negative charge.

💡Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It plays a key role in determining the polarity of a molecule, as a significant electronegativity difference between bonded atoms can lead to a polar bond. The video explains that fluorine has a high electronegativity value of 4.0, which is higher than hydrogen's value of 2.1, causing the electrons in HF to be pulled towards fluorine, making it a polar molecule.

💡Dipole Moment

Dipole moment refers to a measure of the separation of positive and negative electrical charges in a molecule, represented by an arrow pointing from the partial positive charge towards the partial negative charge. The concept is essential in the video for understanding molecular polarity. For instance, in water (H2O), the dipole moments point towards the more electronegative oxygen atom, resulting in a net dipole moment and making the molecule polar.

💡Hydrocarbons

Hydrocarbons are organic compounds consisting only of carbon and hydrogen atoms. The video mentions that hydrocarbons are nonpolar because the electronegativity difference between carbon and hydrogen is not significant enough to create a polar bond. This makes hydrocarbons an important concept for identifying nonpolar molecules.

💡Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is a key concept in the video because the shape of a molecule can influence whether the dipole moments cancel out or result in a net dipole moment, thus determining the molecule's polarity. For example, carbon tetrafluoride has a tetrahedral geometry where the dipole moments cancel out, making it nonpolar, whereas water has a bent shape leading to a net dipole moment and is therefore polar.

💡Polar Bonds

Polar bonds occur when there is a significant electronegativity difference between the atoms involved in the bond, causing an unequal sharing of electrons and a separation of charge. The video emphasizes that the presence of polar bonds is a prerequisite for a molecule to be polar. For example, both carbon dioxide (CO2) and sulfur dioxide (SO2) have polar bonds due to the electronegativity difference between carbon/sulfur and oxygen.

💡Net Dipole Moment

The net dipole moment is the vector sum of all the individual dipole moments in a molecule. It is a critical concept in the video for determining the overall polarity of a molecule. If the net dipole moment is zero, as in CO2, the molecule is nonpolar. In contrast, if the net dipole moment is not zero, as in SO2, the molecule is polar.

💡Electronegativity Difference

Electronegativity difference is the numerical difference in electronegativity values between two atoms in a bond. This concept is vital in the video for identifying polar bonds and, by extension, polar molecules. A difference greater than or equal to 0.5 generally indicates a polar bond, as seen in the comparison between carbon (2.5) and fluorine (4.0) in CF4.

💡Lewis Structure

A Lewis structure is a graphical representation of the valence electrons of an atom or molecule, showing how they are arranged to form chemical bonds. The video uses Lewis structures to analyze the polarity of molecules like CO2 and SO2 by illustrating the electron distribution and helping to predict molecular geometry and polarity.

Highlights

Understanding the concept of polarity in molecules involves recognizing the separation of positive and negative charges within a molecule.

A polar molecule has a part with a positive charge and another with a negative charge, unlike nonpolar molecules where the charge is evenly distributed.

Hydrofluoric acid (HF) is an example of a polar molecule due to the electronegativity difference between hydrogen and fluorine.

In polar molecules, electrons are shared unequally, leading to a partial negative charge on the more electronegative atom and a partial positive charge on the less electronegative one.

Nonpolar molecules, such as hydrogen gas (H2), have an equal sharing of electrons, resulting in an overall neutral charge.

Molecules containing only one type of element, like H2 or O2, are automatically nonpolar due to the uniform distribution of electrons.

Hydrocarbons, which contain only carbon and hydrogen, are also nonpolar because of the relatively equal electron sharing between these atoms.

The electronegativity difference between two elements in a bond must be greater than or equal to 0.5 for the bond to be considered polar.

The geometry of a molecule plays a crucial role in determining its polarity; molecules with symmetrical shapes can be nonpolar despite having polar bonds.

Carbon tetrafluoride (CFC) is an example of a nonpolar molecule with polar bonds, due to the tetrahedral geometry causing the dipole moments to cancel out.

Water (H2O) is a polar molecule because of its bent shape and the unequal sharing of electrons, resulting in a net dipole moment.

The dipole moment is represented by an arrow pointing from the atom with a partial positive charge towards the atom with a partial negative charge.

Carbon dioxide (CO2) is a nonpolar molecule despite having polar bonds, as the linear geometry causes the dipole moments to cancel out.

Sulfur dioxide (SO2) is a polar molecule because the bent shape leads to non-cancelling dipole moments, resulting in a net dipole moment.

To determine if a molecule is polar or nonpolar, one should first check for the presence of only one type of element or hydrocarbons, then analyze the electronegativity difference and molecular geometry.

Polar molecules have a net dipole moment, while nonpolar molecules typically have a dipole moment of zero.

Transcripts

in this video we're gonna talk about how

to tell if a molecule is polar or

nonpolar but first we need to understand

what it means for something to be

pulling and so what I'm gonna do is I'm

gonna draw four objects and I want you

to determine which of these four objects

is polarized

so how would you describe these four

objects let's start with the one on the

upper left so this object has positive

and negative charges so overall this

object is neutral this object you could

describe it as an ion it has a net

positive charge this one you can

describe it as a negatively charged ion

it has a net negative charge the last

object overall it's a neutral

however it's polarized and the reason

why it's polarized is because one side

is positive the other side is negative

and basically a polar molecule has that

feature one part of it has a positive

charge and the other part has a negative

charge so let me give an example of a

polar molecule hydrofluoric acid is a

polar molecule if we draw the structure

there's a single bond between hydrogen

and fluorine and fluorine is highly

electronegative it has an

electronegativity value of 4.0 for

hydrogen

it's 2.1 and so because fluorine is more

electronegative than hydrogen it's going

to pull the electrons toward itself and

so fluorine will acquire a partial

negative charge and hydrogen is going to

be electron deficient it's going to

acquire a partial positive charge so if

we were to draw the molecule this would

be hydrogen and this would be fluorine

fluorine is bigger than hydrogen but

Floyd has a negative charge with respect

to hydrogen and hydrogen has a positive

charge and so this molecule is polar

because one side is positive and the

other side is negative now let's make a

distinction between polar molecules and

nonpolar molecules

in polar molecules you have an unequal

sharing of electrons in nonpolar

molecules the sharing of electrons is

relatively equal so in the case of

hydrofluoric acid fluorine

even though hydrogen and fluorine are

sharing electrons they don't share

equally so that's why fluorine has a

partial negative charge it pulls the

electrons toward itself and the hydrogen

has a partial positive charge so

basically we have this picture one side

is positive and the other side of the

molecule is negative make an HF polar

hydrogen gas is nonpolar because the two

atoms in the molecule are the same the

electrons are shared equally and so if

you were to draw a picture you don't

have a positive and a negative region

overall is simply just neutral and so

nonpolar molecules they don't have that

separation of charge as we see in polar

molecules so anytime you see a molecule

that is made up of one type of element

it's automatically nonpolar so let's go

over some rules because typically if

you're studying for a test you need to

quickly determine if a molecule is polar

or not so let's go over the nonpolar

molecules molecules that contain only

one type of element are automatically

nonpolar such as h2 + 2 O 2 F 2 BR 2 CL

2 I 2 if you see these automatically you

know it's nonpolar now the second thing

you need to watch out for are the

hydrocarbons so if you have a molecule

that contains only carbon and hydrogen

such as methane ethane propane and

things like that it's automatically

nonpolar the carbon hydrogen bond

nonpolar for a bond to be polar the

election negativity difference between

the two elements in that bond has to be

greater than or equal to 0.5 or more the

electronegativity of carbon is about 2.5

and for hydrogen its 2.1 so the

electronegativity difference between

these two elements is point 4 making the

bond nonpolar so hydrocarbons that is

molecules contain an only carbon and

hydrogen are nonpolar so just by knowing

this this is half the battle now the

next thing we need to consider is the

geometry of the molecule because that

can make the difference of the molecule

being polar or nonpolar so let me give

you some examples carbon tetrafluoride

would you say this molecule is polar or

is it nonpolar well first before we

analyze the polarity of the molecule

let's talk about the polarity of the

bond is the carbon fluorine bond polar

or nonpolar the electronegativity of

carbon is 2 point 5 and for fluorine

it's 4.0 so we have an en difference of

1.5 which means that the bond is polar

so not the molecule but the bond but now

what about the molecule is the molecule

as a whole is it a polar or nonpolar

molecule so we need to draw it so we

have four fluorine atoms and the

molecular geometry for it is tetrahedral

so the bond angles are not 90 but 109.5

so technically it's a 3d shape not a 2d

shape now you need to draw something

known as the dipole moment the dipole

moment looks

basically like an arrow that points

starting from the atom with the partial

positive charge but appoints towards the

atom with the partial negative charge

and so the four arrows will look like

this

notice that they all point in opposite

directions these arrows are oriented in

such a way that they all cancel out and

so then that dipole moment for this

molecule is zero so because all of the

dipole moments cancel the molecule as a

whole is nonpolar but the bonds in this

molecule are polar so these are things

you have to look out for

now what about water is water polar or

nonpolar well first let's analyze the

bond the OAH bond hydrogen has an

electronegativity value of 2.1 and for

oxygen is 3.5 so the electronegativity

difference is 1.4 it's greater than 0.5

which means that water has polar bonds

now we need to analyze the geometry of

h2o oxygen like to form two bonds and it

has two lone pairs and because it's more

electronegative it's going to have a

partial negative charge hydrogen will

have a partial positive charge and if we

draw the dipole moments which will point

towards the more electronegative oxygen

atom it's going to look like this so

notice that we have a net dipole moment

in this molecule and so as a result the

molecule is polar now let's talk about

why the two arrows don't cancel and

hopefully you took a course in physics

and you understand how to add vectors

but let's draw two arrows that look like

this

let's call this arrow one arrow to the

first arrow has an X component that goes

towards the right and the y component

that goes up the second arrow has an

excellent point going to the left and

the y component going up notice that the

X components they cancel because they're

opposite to each other

however the Y components they don't

cancel and so they're additive thus

water has in that diaper moment that

goes towards the oxygen atom so this

side is positive and the top part is it

has a partial negative charge and so the

dipole moment goes towards the partial

negative oxygen atom making water polar

so molecules that have a net dipole

moment are polar and nonpolar molecules

typically have a dipole moment of zero

so keep that in mind now let's go over

two more examples carbon dioxide and

sulfur dioxide which of these two

molecules is polar and which one is

nonpolar feel free to pause the video

and work on this example now the best

thing to do is to draw the Lewis

structure

carbon dioxide is a linear molecule

sulfur dioxide has a bent shape now both

carbon and sulfur they both have an

electronegativity value of 2.5 and we

know oxygen has an en value of 3.5 so in

both cases the carbon oxygen bond and

the sulfur oxygen bond are both polar

because they both contain an en

difference of 1 so they both have polar

bonds now let's draw the partial charges

in both cases oxygen will carry a

negative partial charge and carbon and

sulfur will have a partial positive

charge

because they're less electronegative

than oxygen now let's draw the dipole

moments in the case of carbon dioxide

notice that the dipole moments they're

opposite to each other so they

completely cancel so this has a dipole

moment of zero which means that co2 is a

non-polar molecule even though it has

polar bonds now in the case of sulfur

dioxide the dipole moments do not

completely cancel the X components they

cancel because they're opposite to each

other but the Y components of the dipole

moment they're in the same direction so

they add up which means that then that

type of moment for this structure is in

a negative Y direction based on the way

it's drawn and so because sulfur dioxide

has a dipole moment that is greater than

zero we don't know what the number is

but you can look it up because it's not

equal to zero this molecule is polar and

so now you know how to tell if a

molecule is polar or nonpolar so step

one look out for any elements or look

out for any molecules that contain only

one type of element like h2 and 202 if

they only have one type of element it's

automatically nonpolar step 2

look out for any hydrocarbons so if you

see a molecule that has only carbon and

hydrogen it's nonpolar step 3 for other

molecules that are composed of different

elements like hf h2o co2 the best thing

to do is to draw the Lewis structure and

then see if the dipole moments if they

cancel or if there's a net dipole moment

and also check the bonds to make sure

the bonds are polar as well and so

that's all I got for this video

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take a look at that when you get a

chance thanks again for watching