Electronegativity | Atomic structure and properties | AP Chemistry | Khan Academy

Summary

This video script explores electronegativity and electron affinity, explaining how they relate to an atom's attraction to electrons. It uses the example of a water molecule to illustrate how differing electronegativities between hydrogen and oxygen create partial charges, affecting water's properties. The script also discusses how electronegativity trends across the periodic table, increasing from left to right and decreasing from top to bottom, influencing chemical reactivity and bonding.

Takeaways

• 🔬 Electronegativity and electron affinity are closely related concepts in chemistry.
• 🌐 Electron affinity refers to an atom's attraction to electrons, while electronegativity specifically describes how an atom behaves when sharing electrons in a covalent bond.
• 🐷 'Hogging electrons' is an informal way to describe an atom's tendency to attract electrons towards itself within a covalent bond.
• 💧 The water molecule (H2O) is used as an example to illustrate how electronegativity affects the sharing of electrons between different atoms.
• ⚛️ Hydrogen atoms in a water molecule are stable when they share electrons with oxygen, which has a higher electronegativity and thus attracts the shared electrons more strongly.
• 🚫 The unequal sharing of electrons due to differing electronegativities results in a polar covalent bond, leading to partial charges on the atoms.
• 📚 Understanding electronegativity is crucial for predicting chemical reactions and the formation of molecules, especially in organic chemistry.
• ⬅️ Electronegativity increases from left to right across a period in the periodic table, as atoms become more stable by gaining electrons.
• ⬇️ Electronegativity decreases as you move down a group in the periodic table due to the increasing distance of the outermost electrons from the nucleus.
• 🏔️ The most electronegative elements are found at the top right of the periodic table, while the least electronegative are at the bottom left.

Q & A

What are the main concepts discussed in the video?

The video discusses the concepts of Electronegativity and Electron Affinity, explaining how they relate to an atom's attraction to electrons and its behavior in covalent bonds.

How is Electron Affinity defined in the context of the video?

Electron Affinity is defined as the measure of how much an atom attracts electrons or its desire to gain additional electrons.

What does it mean to 'hog electrons' in the context of electronegativity?

To 'hog electrons' refers to an atom's tendency to attract and keep electrons closer to itself rather than sharing them equally in a covalent bond.

Why is the water molecule used as an example in the video?

The water molecule is used as an example because it illustrates the difference in electronegativity between hydrogen and oxygen, which results in polar covalent bonds.

How does the video explain the electron configuration of hydrogen and oxygen in a water molecule?

The video explains that hydrogen atoms have one valence electron and would be stable if they could gain another electron, while oxygen has six valence electrons and would be stable if it could gain two more electrons to complete its octet.

What is the significance of electronegativity differences in the formation of water molecules?

The difference in electronegativity between oxygen and hydrogen causes the electrons in the covalent bonds to spend more time around the oxygen, leading to a partial negative charge on the oxygen and partial positive charges on the hydrogens, which contributes to water's unique properties.

How does electronegativity affect the properties of a molecule?

Electronegativity differences between atoms in a molecule can lead to polar bonds, which in turn affect the molecule's physical and chemical properties, such as solubility and reactivity.

What trend does electronegativity follow as you move across a period in the periodic table?

Electronegativity increases from left to right across a period in the periodic table because atoms on the right side have a greater tendency to attract electrons due to higher nuclear charge.

What trend does electronegativity follow as you move down a group in the periodic table?

Electronegativity decreases as you move down a group because the outermost electrons are farther from the nucleus and are less attracted to it, making the atom less likely to attract additional electrons.

Which elements are considered the most electronegative?

The most electronegative elements are found in the top right of the periodic table, such as the halogens.

Which elements are considered the least electronegative?

The least electronegative elements are found in the bottom left of the periodic table, such as the alkali metals and alkaline earth metals.

Outlines

00:00

🔬 Electronegativity and Electron Affinity

This paragraph introduces the concepts of electronegativity and electron affinity. Electronegativity refers to the tendency of an atom to attract electrons when it is part of a covalent bond, essentially how much it 'hogs' electrons from another atom it's bonded with. Electron affinity, on the other hand, is the measure of an atom's attraction to additional electrons. The paragraph explains that these two concepts are closely related, with atoms that have high electronegativity also tending to have high electron affinity. The example of a water molecule (H2O) is used to illustrate these concepts, highlighting how hydrogen and oxygen atoms share electrons to achieve stability, with oxygen being more electronegative and thus hogging the electrons more, leading to a polar molecule with distinct partial charges.

05:01

📈 Trends in Electronegativity

This paragraph discusses the trends in electronegativity across the periodic table. It starts by explaining that electronegativity increases as you move from left to right within a period, using sodium and chlorine as examples. Sodium, being a group one element, is more likely to lose an electron to achieve a stable electron configuration like neon, while chlorine, being a halogen, would prefer to gain an electron to complete its outer shell like argon. Consequently, chlorine is more electronegative than sodium. The trend continues as you move down a group, with electronegativity decreasing. This is because atoms get larger, and their outermost electrons are less attracted to the nucleus, making it easier for them to lose electrons. The most electronegative elements are found at the top right of the periodic table, while the least electronegative are at the bottom left.

Keywords

💡Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is a key concept in understanding how atoms bond and share electrons. In the video, electronegativity is discussed in the context of covalent bonds, where it is used to describe how likely an atom is to 'hog' electrons when sharing with another atom. The example of a water molecule (H2O) is used to illustrate how oxygen, being more electronegative than hydrogen, pulls electrons closer to itself, creating a partial negative charge on the oxygen and partial positive charges on the hydrogens.

💡Electron Affinity

Electron affinity refers to the energy change associated with an atom's attraction to an additional electron. It is closely related to electronegativity but is a broader concept, as it does not necessarily involve sharing electrons in a bond. The video script mentions electron affinity in the context of how much an atom 'likes' electrons, using the example of oxygen wanting to gain two more electrons to achieve a stable electron configuration like neon.

💡Covalent Bond

A covalent bond is a chemical bond formed by the sharing of electron pairs between atoms. This concept is central to the video's discussion of electronegativity and electron affinity. The script explains that electronegativity is specifically about how atoms behave when they are part of a covalent bond, sharing electrons with other atoms.

💡Hogging Electrons

The phrase 'hogging electrons' is used informally in the video to describe the tendency of an atom to attract and hold onto electrons in a covalent bond more than its bonded partner. This behavior is indicative of high electronegativity. The video uses this term to explain how oxygen, being more electronegative, 'hogs' electrons from hydrogen in a water molecule.

💡Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom, which are involved in chemical bonding. The video discusses valence electrons in the context of hydrogen and oxygen atoms, explaining how hydrogen has one valence electron and would be stable if it could gain another to mimic helium's electron configuration, while oxygen has six and would be stable with two more, like neon.

💡Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. The video script draws a parallel between ionization energy and electronegativity, suggesting that atoms with low ionization energy, like sodium, are more likely to lose an electron and thus have lower electronegativity.

💡Atomic Radii

Atomic radii refer to the size of an atom, typically measured from the nucleus to the outermost electron shell. The video uses atomic radii to explain trends in electronegativity as one moves down a group in the periodic table. Larger atoms, like cesium, have a larger atomic radius, making their valence electrons less tightly held and thus less electronegative.

💡Partial Charges

Partial charges are the result of the unequal sharing of electrons in a covalent bond, leading to a separation of charge within the molecule. The video explains how the difference in electronegativity between hydrogen and oxygen in water molecules results in partial negative charges on oxygen and partial positive charges on hydrogen.

💡Periodic Table Trends

The video discusses how electronegativity trends across the periodic table, increasing from left to right within a period and decreasing as one moves down a group. This trend is used to predict the electronegativity of elements and is illustrated by comparing sodium and chlorine, where chlorine's higher electronegativity is attributed to its desire to gain an electron to complete its shell.

💡Noble Gases

Noble gases are a group of chemical elements with full valence electron shells, making them stable and unreactive. The video mentions that noble gases are not very electronegative because they are already stable and do not form covalent bonds readily.

💡Electron Configuration

Electron configuration refers to the distribution of electrons in an atom or molecule's orbitals. The video uses the term to describe the stable electron configurations that atoms like hydrogen and oxygen aim to achieve through bonding, such as hydrogen mimicking helium and oxygen neon.

Highlights

Electronegativity and electron affinity are closely related concepts.

Electron affinity measures how much an atom attracts electrons.

Electronegativity is the tendency of an atom to attract electrons in a covalent bond.

Atoms with high electronegativity tend to hog electrons in covalent bonds.

Electronegativity is more specific than electron affinity.

Electronegativity can be understood through the example of a water molecule.

In a water molecule, oxygen is more electronegative than hydrogen.

The difference in electronegativity between oxygen and hydrogen leads to polar covalent bonds in water.

Electronegativity is crucial for understanding chemical reactions and molecular formation.

Electronegativity trends can be predicted by considering ionization energy.

Electronegativity increases from left to right across a period in the periodic table.

Electronegativity decreases as you move down a group in the periodic table.

The most electronegative elements are found at the top right of the periodic table.

The least electronegative elements are found at the bottom left of the periodic table.

Noble gases are not very reactive due to their complete electron shells.

Electronegativity helps predict the likelihood of reactions in organic chemistry.

The trend in electronegativity across the periodic table is from bottom left to top right.

Transcripts

Voiceover: What I want to talk about in this video

are the notions of Electronegativity,

electro, negati, negativity,

and a closely, and a closely related

idea of Electron Affinity, electron affinity.

And they're so closely related that in general,

if something has a high electronegativity,

they have a high electron affinity,

but what does this mean?

Well, electron affinity is how much does that atom

attract electrons, how much does it like electrons?

Does it want, does it maybe want more electrons?

Electronegativity is a little bit more specific.

It's when that atom is part of a covalent bond,

when it is sharing electrons with another atom,

how likely is it or how badly does it want

to hog the electrons in that covalent bond?

Now what do I mean by hogging electrons?

So let me make, let me write this down.

So how badly wants to hog,

and this is an informal definition clearly,

hog electrons, keep the electrons,

to spend more of their time closer to them

then to the other party in the covalent bond.

And this is how, how much they like electrons,

or how much affinity they have towards electrons.

So how much they want electrons.

And you can see that these are very,

these are very related notions.

This is within the context of a covalent bond,

how much electron affinity is there?

Well this, you can think of it as a slightly broader notion,

but these two trends go absolutely in line with each other.

And to think about, to just think about

electronegativity makes it a little bit more tangible.

Let's think about one of the most famous

sets of covalent bonds,

and that's what you see in a water molecule.

Water, as you probably know, is H two O,

you have an oxygen atom,

and you have two hydrogens.

Each of the hydrogen's have one valence electron,

and the oxygen has, we see here, at it's outermost shell,

it has one, two, three, four, five, six valence electrons.

One, two, three, four, five, six valence electrons.

And so you can imagine, hydrogen would be happy

if it was able to somehow pretend like it had another

electron then it would have an electron configuration

a stable, first shell that only requires two electrons,

the rest of them require eight,

hydrogen would feel, hey I'm stable like helium

if it could get another electron.

And oxygen would feel, hey I'm stable like neon

if I could get two more electrons.

And so what happens is they share each other's electrons.

This, this electron can be shared in conjunction

with this electron for this hydrogen.

So that hydrogen can kind of feel like it's using

both and it gets more stable,

it stabilizes the outer shell,

or it stabilizes the hydrogen.

And likewise, that electron could be,

can be shared with the hydrogen,

and the hydrogen can kind of feel more like helium.

And then this oxygen can feel like

it's a quid pro quo,

it's getting something in exchange for something else.

It's getting the electron, an electron,

it's sharing an electron from each of these hydrogens,

and so it can feel like it's, that it stabilizes it,

similar to a, similar to a neon.

But when you have these covalent bonds,

only in the case where they are equally

electronegative would you have a case

where maybe they're sharing,

and even there what happens

in the rest of the molecule might matter,

but when you have something like this,

where you have oxygen and hydrogen,

they don't have the same electronegativity.

Oxygen likes to hog electrons more than hydrogen does.

And so these electrons are not gonna spend

an even amount of time.

Here I did it kind of just drawing these,

you know, these valence electrons as these dots.

But as we know, the electrons are in this

kind of blur around, around the,

around the actual nuclei,

around the atoms that make up the atoms.

And so, in this type of a covalent bond,

the electrons, the two electrons that this bond represents,

are going to spend more time around the oxygen

then they are going to spend around the hydrogen.

And these, these two electrons are gonna spend

more time around the oxygen,

then are going to spend around the hydrogen.

And we know that because oxygen is more electronegative,

and we'll talk about the trends in a second.

This is a really important idea in chemistry,

and especially later on as you study organic chemistry.

Because, because we know that

oxygen is more electronegative,

and the electrons spend more time

around oxygen then around hydrogen,

it creates a partial negative charge on this side,

and partial positive charges on this side right over here,

which is why water has many of the properties that it does,

and we go into much more in depth in that in other videos.

And also when you study organic chemistry,

a lot of the likely reactions that are

going to happen can be predicted,

or a lot of the likely molecules that form

can be predicted based on elecronegativity.

And especially when you start going

into oxidation numbers and things like that,

electronegativity will tell you a lot.

So now that we know what electronegativity is,

let's think a little bit about what is,

as we go through, as we start,

as we go through, as we go through a period,

as say as we start in group one,

and we go to group, and as we go all the way

all the way to, let's say the halogens,

all the way up to the yellow column right over here,

what do you think is going to be

the trend for electronegativity?

And once again, one way to think about it

is to think about the extremes.

Think about sodium, and think about chlorine,

and I encourage you to pause

the video and think about that.

Assuming you've had a go at it,

and it's in some ways the same idea,

or it's a similar idea as ionization energy.

Something like sodium has only one electron

in it's outer most shell.

It'd be hard for it to complete that shell,

and so to get to a stable state it's much easier

for it to give away that one electron that it has,

so it can get to a stable configuration like neon.

So this one really wants to give away an electron.

And we saw in the video on ionization energy,

that's why this has a low ionization energy,

it doesn't take much energy, in a gaseous state,

to remove an electron from sodium.

But chlorine is the opposite.

It's only one away from completing it's shell.

The last thing it wants to do is give away electron,

it wants an electron really, really, really, really badly

so it can get to a configuration of argon,

so it can complete its third shell.

So the logic here is that sodium wouldn't mind

giving away an electron,

while chlorine really would love an electron.

So chlorine is more likely to hog electrons,

while sodium is very unlikely to hog electrons.

So this trend right here,

when you go from the left to the right,

your electronegativity, let me write this,

your getting more electronegative.

More electro, electronegative, as you,

as you go to the right.

Now what do you think the trend is going to be

as you go down, as you go down in a group?

What do you think the trend is going to be as you go down?

Well I'll give you a hint.

Think about, think about atomic radii, and given that,

pause the video and think about

what do you think the trend is?

Are we gonna get more or less electronegative

as we move down?

So once again I'm assuming you've given a go at it,

so as we know, from the video on atomic radii,

our atom is getting larger, and larger, and larger,

as we add more and more and more shells.

And so cesium has one electron in it's outer most shell,

in the sixth shell,

while, say, lithium has one electron.

Everything here, all the group one elements,

have one electron in it's outer most shell,

but that fifty fifth electron,

that one electron in the outer most shell in cesium,

is a lot further away then the outer most electron

in lithium or in hydrogen.

And so because of that, it's, well one,

there's more interference between that electron and the

nucleus from all the other electrons in between them,

and also it's just further away,

so it's easier to kind of grab it off.

So cesium is very likely to give up,

it's very likely to give up electrons.

It's much more likely to give up electrons than hydrogen.

So, as you go down a given group,

you're becoming less, less electronegative, electronegative.

So what, what are, based on this,

what are going to be the most electronegative

of all the atoms?

Well they're going to be the ones

that are in the top and the right of the periodic table,

they're going to be these right over here.

These are going to be the most electronegative,

Sometimes we don't think as much about the noble gases

because they aren't, they aren't really that reactive,

they don't even form covalent bond,

because they're just happy.

While these characters up here,

they sometimes will form covalent bonds,

and when they do, they really like to hog those electrons.

Now what are the least electronegative,

sometimes called very electropositive?

Well these things down here in the bottom left.

These, over here, they have only,

you know in the case of cesium,

they have one electron to give away

that would take them to a stable state like, like xenon,

or in the case of these group two elements

they might have to give away two,

but it's much easier to give away two

then to gain a whole bunch of them.

And they're big, they're big atoms.

So those outer most electrons are getting

less attracted to the positive nucleus.

So the trend in the periodic table

as you go from the bottom left,

to the top right,

you're getting more, more electro, electronegative.