Polar, Non-Polar, and Ionic Compounds: Explanation, Examples, and Practice

Summary

This video explains the concept of polarity in chemistry by examining the electronegativity differences between atoms in a molecule. It covers how to determine if a bond is polar or nonpolar using electronegativity values, with examples like HCl and N2. The video also explores how molecular shape and symmetry, as seen in molecules like CCl4 and H2O, affect overall polarity. It emphasizes the influence of lone pairs of electrons on molecular structure, helping viewers understand why some molecules are polar and others nonpolar.

Takeaways

• 🔬 To determine molecular polarity, start by examining individual chemical bonds and then the molecule as a whole.
• 📊 Electronegativity values are crucial for understanding bond polarity; differences greater than 0.5 indicate polar bonds, while differences below 0.5 suggest nonpolar bonds.
• 📚 A condensed periodic table is a useful tool for quickly referencing electronegativity values of elements.
• 🧲 Polar molecules, like HCl, have electronegativity differences between atoms that fall between 0.5 and 2.0.
• 🌐 The electronegativity trend across the periodic table shows that atoms become more electronegative as you move towards fluorine.
• 🔄 Nonpolar diatomic molecules, such as N2, have equal electronegativity values, resulting in no polarity.
• 📐 The shape and symmetry of a molecule are critical in determining its overall polarity, even if individual bonds are polar.
• 🌐 For molecules like CCl4, although each carbon-chlorine bond is polar, the symmetrical tetrahedral structure results in a nonpolar molecule.
• 🔑 Lone pairs of electrons, as seen in NH3 and H2O, can significantly influence a molecule's shape and polarity, leading to polar molecules despite the presence of polar bonds.
• 🌟 Polarity is a fundamental concept in science, affecting how molecules interact in various applications, from pharmaceuticals to construction materials.

Q & A

What is electronegativity and how is it relevant to bond polarity?

Electronegativity refers to an atom's ability to attract shared electrons in a chemical bond. It is relevant to bond polarity because the difference in electronegativity between two atoms determines whether a bond is polar or nonpolar.

How do we classify bonds based on electronegativity differences?

Bonds are classified based on the difference in electronegativity: if the difference is above 2.0, it's considered an ionic bond; between 2.0 and 0.5, the bond is polar; and below 0.5, the bond is nonpolar.

Why is HCl (hydrochloric acid) considered a polar molecule?

HCl is considered polar because the electronegativity difference between hydrogen (2.20) and chlorine (3.16) is 0.96, which falls between 0.5 and 2.0, making it a polar bond.

What makes diatomic molecules like N2 and O2 nonpolar?

Diatomic molecules like N2 and O2 are nonpolar because the electronegativity difference between identical atoms is zero, meaning the electrons are shared equally, resulting in no charge separation.

Why is carbon tetrachloride (CCl4) considered nonpolar even though its individual bonds are polar?

CCl4 is nonpolar because, although each C-Cl bond is polar, the molecule's symmetrical tetrahedral shape causes the dipoles to cancel out, making the molecule nonpolar overall.

What is the role of lone pairs in determining molecular polarity?

Lone pairs can affect molecular shape, influencing whether a molecule is polar or nonpolar. For example, in NH3, the lone pair on nitrogen creates a pyramidal shape, making the molecule polar due to the unequal distribution of charge.

How do we determine if a larger molecule is polar or nonpolar?

To determine if a larger molecule is polar or nonpolar, we first examine the Lewis structure, then calculate the electronegativity differences of individual bonds, and finally assess the shape and symmetry of the molecule.

Why is water (H2O) a polar molecule?

Water is a polar molecule because its H-O bonds are polar, and the molecule's bent shape (due to two lone pairs on oxygen) creates a distinct positive and negative side, leading to an unequal charge distribution.

What is the significance of polarity in real-world applications?

Polarity plays a crucial role in determining how molecules interact, affecting everything from the behavior of medicines in the body to the properties of building materials.

What does it mean for a molecule to have a 'tetrahedral structure,' and how does this affect its polarity?

A tetrahedral structure refers to a molecule where a central atom is symmetrically surrounded by four other atoms. This symmetrical arrangement can cause dipoles to cancel out, often resulting in a nonpolar molecule, as in the case of CCl4.

Outlines

00:00

🔬 Understanding Chemical Bond Polarity

This section introduces the concept of polarity in chemical bonds by analyzing the electronegativity of individual atoms. It explains how differences in electronegativity determine whether a bond is polar or nonpolar. Using the example of HCl, it shows how to calculate this difference and provides a continuum for classifying bonds as ionic, polar, or nonpolar. The section highlights the trend of electronegativity in the periodic table and emphasizes the importance of memorizing values to understand bond polarity.

05:02

📐 Symmetry and Molecular Polarity

This section focuses on how the symmetry of molecules influences their overall polarity, even if individual bonds are polar. Using CCl4 (carbon tetrachloride) as an example, it explains how symmetrical tetrahedral structures can result in nonpolar molecules. The section introduces steps for determining molecular polarity: drawing Lewis structures, evaluating individual bonds, and considering molecular shape and symmetry.

Keywords

💡Polarity

Polarity refers to the distribution of electric charge across a molecule, which affects how it interacts with other molecules. In the video, polarity is discussed in terms of both individual chemical bonds and the entire molecule. For example, HCl is identified as a polar molecule due to the difference in electronegativity between hydrogen and chlorine.

💡Electronegativity

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. It is a core concept in determining bond polarity. In the video, electronegativity values for different atoms, such as hydrogen (2.20) and chlorine (3.16), are used to assess whether a bond is polar or nonpolar.

💡Lewis structure

A Lewis structure is a diagram that shows the bonds between atoms and the lone pairs of electrons that may exist in a molecule. The video uses Lewis structures to help visualize molecular geometry and bond polarity. For example, the Lewis structure for H2O helps illustrate why it is a polar molecule.

💡Ionic bond

An ionic bond is formed when the difference in electronegativity between two atoms is greater than 2.0, leading to a complete transfer of electrons from one atom to another. The video mentions this when discussing the continuum of chemical bonds, noting that bonds with a large electronegativity difference, like in ionic compounds, are classified as ionic.

💡Covalent bond

A covalent bond is a type of chemical bond where atoms share electrons. Covalent bonds can be polar or nonpolar, depending on the difference in electronegativity. For instance, the video explains that N2 is a nonpolar covalent molecule since the electronegativity difference between the two nitrogen atoms is zero.

💡Nonpolar molecule

A nonpolar molecule has an even distribution of electrons, resulting in no distinct positive or negative poles. In the video, molecules like N2 and I2 are examples of nonpolar molecules because their atoms have identical electronegativity values, leading to a symmetrical distribution of charge.

💡Symmetry

Symmetry in molecules refers to how the atoms and bonds are arranged in space, which affects whether a molecule is polar or nonpolar. The video uses symmetry to explain why a molecule like CCl4, despite having polar bonds, is overall nonpolar due to its symmetrical tetrahedral structure.

💡Lone pairs

Lone pairs are pairs of electrons that are not shared between atoms but belong to a single atom. These unbonded electrons influence the shape and polarity of molecules. For instance, in NH3 and H2O, lone pairs cause the molecules to be asymmetrical and polar, as shown in the video.

💡Tetrahedral structure

A tetrahedral structure is a molecular shape where a central atom is bonded to four other atoms positioned at the corners of a tetrahedron. The video describes CCl4 as having a tetrahedral structure, which makes the molecule symmetrical and nonpolar, despite the individual polar bonds.

💡Bonded electron pairs

Bonded electron pairs are electrons shared between two atoms to form a covalent bond. In the video, bonded pairs are contrasted with lone pairs, and their unequal sharing in polar molecules like HCl contributes to bond polarity.

Highlights

Introduction to polarity by examining individual chemical bonds and entire molecules.

Explanation of how electronegativity differences determine bond polarity: polar, nonpolar, and ionic bonds.

Description of how to calculate the difference in electronegativity using the periodic table, with HCl as an example.

Classification of bonds based on electronegativity differences: above 2.0 is ionic, between 2.0 and 0.5 is polar, and below 0.5 is nonpolar.

Detailed calculation showing HCl as a polar molecule due to its electronegativity difference of 0.96.

Examples of polar molecules: HF, HBr, and NH3, emphasizing the role of electronegativity.

Explanation of the trend in electronegativity on the periodic table, increasing towards fluorine.

Discussion on noble gases and their typically negligible electronegativity in chemical bonds.

Example of nonpolar diatomic molecules like N2, O2, and F2 due to zero electronegativity difference.

Steps to determine polarity in larger molecules: draw Lewis structures, check individual bonds, and assess shape and symmetry.

Example of carbon tetrachloride (CCl4) as a symmetrical, nonpolar molecule despite polar bonds due to its tetrahedral structure.

Analysis of CH3Cl as a polar molecule because of its asymmetrical shape and the presence of a polar C-Cl bond.

Explanation of the influence of lone pairs on molecular shape and polarity, using NH3 as an example of a polar molecule with a pyramidal structure.

Detailed example of H2O showing that lone pairs create an asymmetrical structure, making water a polar molecule.

Conclusion emphasizing the importance of polarity in understanding molecular interactions, with applications in medicine and materials science.

Transcripts

to understand polarity we'll first look

at individual chemical bonds and then

the entire molecule let's look at

polarity between two atoms first

each atom has a specific value for its

electronegativity to figure out if a

bond is polar or nonpolar we look at the

difference between these values

let's look at a condensed periodic table

with the values we'll use most

frequently let's try hcl hydrochloric

acid hydrogen has a value of 2.20 and

chlorine has a value of 3.16

the difference between these

2.20 minus 3.16 gives us 0.96

that's the difference in

electronegativity for h and cl

but what does that number mean chemical

bonds can be classified along a

continuum if the difference in

electronegativity is above 2.0 it's an

ionic bond we consider molecules between

2.0 and 0.5 to be polar and below 0.5 is

nonpolar

these are just guides you may be given

slightly different values back to hcl we

found the difference in

electronegativity to be 0.96

meaning that hcl is considered a polar

molecule

other examples of polar molecules

hf

hbr nhi

we've been talking about

electronegativity

often written as en is the ability of

atoms to attract shared electrons those

are the electrons that are between atoms

when we draw lewis structures

as we've seen in the periodic table

atoms have different values for

electronegativity

the trend is that atoms are more

electronegative as you move towards

fluorine

for group 18 the noble gases they rarely

form chemical bonds and we don't really

consider their electronegativity to be

important

so we know hcl is a polar molecule with

its difference in electronegativity

greater than 0.5 but less than 2.0

for something like n2 nitrogen gas we

can look up the value for n which is

3.04

so 3.04 minus 3.04 is 0.

back to our continuum we see that the

difference below 0.5 is nonpolar

covalent

at this point you probably realize you

need to memorize the numbers in our

continuum

when we have diatomic molecules like o2

n2 f2 these will always be nonpolar

because the difference when we subtract

the electronegativity values we'll be

zero

pause and take a moment to figure out if

each one of these molecules is polar or

nonpolar

for hf we have a difference of 1.78

meaning this is going to be a very polar

molecule with those shared electrons

spending most of their time around the

fluorine atom

for brcl the difference is

0.20

we can have different atoms and still

have a nonpolar bond

for i2 they're the same we'll have an

electronegativity value of zero that

means i2 is nonpolar

we can now find the bond polarity

between two atoms and even do simple

atoms like hcl or n2

next up we want to look at polarity in

larger molecules it's useful to follow

these steps

first have the lewis structure

second

we'll look at the individual bonds just

like we've been doing in this video and

finally we'll look at the shape and the

symmetry to figure out if the molecule

is polar or nonpolar overall

we'll start with ccl4 carbon

tetrachloride carbon has a value of 2.55

and cl has a value of 3.16

the difference between these two numbers

is 0.61

so we know that each bond is going to be

polar

we can write the structure like this

the arrows point towards the more

electronegative atom the delta symbol

that shows the charge

here cl has a negative charge because

it's more electronegative

at this point we've looked at the lewis

structure and we've calculated the

electronegativity difference between the

bonds each carbon-chlorine bond is polar

but be careful this alone won't tell us

if the whole molecule is polar or

nonpolar we need to consider the

symmetry of the molecule to answer that

question

ccl4 is a symmetrical molecule so watch

what happens we have a carbon here in

the center and we're going to add

chlorines so we add one chlorine and

then we add the second one and they

spread out they push away from each

other

the reason they do that is this atom

here the surface are all the electrons

and electrons are negative so when i try

to put two negatives together they'll

spread out

if i add another one

they spread out again you can see that

they're equidistant

and finally i'll add the fourth cl so we

have ccl4 and they're spread out in this

tetrahedral structure

this is symmetrical any angle you look

at it it's pretty much the same

that means that the surface of the

molecule will be the same everywhere

there'll be no poles and it won't be

polar

tetrahedral shaped molecules would be

nonpolar if they consist of carbon and

four of the same type of atoms attached

to that carbon

using the steps we've just covered pause

and try to figure out if ch3cl

is polar or nonpolar

for ch3cl we have the lewis structure

here

and we can calculate the en difference

for each of the bonds

you can see that ccl that's a polar bond

well the c h bond is nonpolar

so with our lewis structure we can take

a look at the actual shape of the entire

molecule we see we have the carbon with

four atoms attached and we know those

are going to spread out and form a

tetrahedral structure

we can see that we have two sides to

this molecule we have a side with the

chlorine atom which is more

electronegative and that means those

shared electrons between the chlorine

and the carbon will spend more time

around the chlorine atom making it more

negative

that means we have a negative pole and a

positive pole and a polar molecule

up until now we've only talked about

electrons that are between atoms they're

bonded electron pairs

we also have pairs of electrons that are

called unbonded electron pairs or lone

pairs they are not in between atoms but

they do have their own orbitals and that

means they influence the shape the

polarity and the symmetry of a molecule

nh3 is an excellent example

first we'll draw the lewis structure for

nh3

next we can calculate the differences in

electronegativity between bonds and we

see that the nh bond is indeed polar

but let's go back and look at the shape

of the molecule to see if it's

symmetrical

we have our nitrogen atom in the middle

and let's add three hydrogen atoms

as we add them they spread out to be as

far away from each other as possible

and we have this structure

when you look at it it looks like it

should be nonpolar each of the hydrogens

is pulling in an opposite direction and

they should cancel out

but we need to go back to our lewis

structure because we have a lone pair of

electrons we have to consider

when we add the lone pair

it influences the shape it actually

pushes down the hydrogens and now we

have a pyramidal also called pyramidal

structure

so the structure is no longer

symmetrical and that means we're going

to have a positive and a negative side

and we're going to have a polar molecule

it's important to stress that polarity

results from an unequal sharing of

electrons the ones that are bonded

shared between atoms but it also results

from the shape or the symmetry of the

molecule and this can be influenced by

unbonded electrons like we saw with nh3

let's take a look at one more

pause and determine if h2o is a polar or

nonpolar molecule

we'll first look at the lewis structure

for h2o

and then we'll calculate the difference

between bonds we can see that that h o

bond that's a polar bond

next let's look at the shape of the h2o

molecule to see if we have symmetry

so we'll start with our oxygen atom and

we'll put two hydrogen atoms on that

they spread out to be as far away as

possible from each other and it looks

like it would be symmetrical like these

two hydrogens would cancel out

however we have our lone pairs two of

them we'll put one

two

and now we can see that the molecule is

no longer symmetrical we have a distinct

top and bottom

because we have this distinct top and

bottom to the molecule water is a polar

molecule

polarity is a hugely important topic in

science everything from medicines to

building materials how the molecules

interact is largely a function of their

polarity to figure that out we drew the

lewis structures

then we looked at the individual bonds

the electronegativity difference between

those bonds finally we looked at the

shape and the symmetry including those

lone pair electrons to figure out if the

molecule was polar or nonpolar

this is dr b with polar and nonpolar

molecules and thanks for watching

you