First and second ionization energy | Atomic structure and properties | AP Chemistry | Khan Academy

Summary

This educational video explores the concept of ionization energy, focusing on the first and second ionization energies of lithium. It explains how lithium, with an atomic number of 3, forms a neutral atom with three electrons, and the energy required to remove these electrons sequentially. The first ionization energy is approximately 520 kJ/mol, while the significantly higher second ionization energy is about 7,298 kJ/mol. The video delves into factors such as nuclear charge, electron shielding, and distance from the nucleus to explain the large difference between the two ionization energies, illustrating why lithium tends to form a +1 cation rather than a +2.

Takeaways

• 🔬 The video compares the first and second ionization energies using lithium as an example.
• 🚀 Lithium has an atomic number of 3, with three protons and three electrons in a neutral atom, configured as 1s² 2s¹.
• ⚡ The first ionization energy of lithium is approximately 520 kilojoules per mole, which removes the outermost electron.
• 💥 After the first ionization, lithium becomes a lithium ion (Li⁺) with an electron configuration of 1s².
• 🔋 The second ionization energy is significantly higher, at about 7,298 kilojoules per mole, removing the next electron.
• ⚛ The second ionization results in a lithium ion with a +2 charge (Li²⁺) and an electron configuration of 1s¹.
• 🌐 The large difference between the first and second ionization energies is attributed to three factors: nuclear charge, electron shielding, and distance from the nucleus.
• 💡 Nuclear charge remains the same for both ionizations, but effective nuclear charge changes due to fewer electrons to shield the nucleus.
• 🛡 Electron shielding reduces the attractive force experienced by the outer electron, but this effect is lessened after the first ionization.
• 📏 The distance of the electron from the nucleus plays a role, with closer electrons experiencing a stronger attractive force and requiring more energy to remove.
• 🧲 The second electron is harder to remove due to less shielding and feeling a stronger effective nuclear charge.
• 🌟 The significant jump in ionization energy between the first and second can indicate the preference for an element to form a specific ion, in this case, Li⁺ over Li²⁺.

Q & A

What is the atomic number of lithium?

Lithium has an atomic number of 3, which means it has three protons in its nucleus.

How many electrons are there in a neutral atom of lithium?

In a neutral atom of lithium, the number of electrons equals the number of protons, so there are three electrons.

What is the electron configuration of lithium?

The electron configuration of lithium is 1s² 2s¹, indicating two electrons in the 1s orbital and one in the 2s orbital.

What is the first ionization energy of lithium, and what does it represent?

The first ionization energy of lithium is approximately 520 kilojoules per mole, which is the energy required to remove the outermost electron from a neutral lithium atom.

What is the resulting ion when the first electron is removed from lithium?

After the first electron is removed, lithium becomes a lithium plus 1 cation, with an electron configuration of 1s².

What is the second ionization energy of lithium, and how does it compare to the first?

The second ionization energy of lithium is approximately 7,298 kilojoules per mole, which is significantly higher than the first ionization energy of 520 kilojoules per mole.

Why is the second ionization energy of lithium much higher than the first?

The second ionization energy is higher because, after the first electron is removed, the remaining electron feels a greater effective nuclear charge due to less electron shielding, and it is also closer to the nucleus, requiring more energy to be removed.

What is the electron configuration of lithium after the second electron is removed?

After the second electron is removed, lithium has a 1s¹ electron configuration, forming a lithium plus 2 cation.

What is effective nuclear charge, and how does it differ between a neutral lithium atom and a lithium plus 1 cation?

Effective nuclear charge is the net positive charge experienced by an electron, taking into account electron shielding. In a neutral lithium atom, the effective nuclear charge for the outer electron is approximately +1.3, while in a lithium plus 1 cation, the single remaining electron experiences the full nuclear charge of +3 due to less shielding.

What role does electron shielding play in ionization energy?

Electron shielding reduces the effective nuclear charge experienced by outer electrons, making it easier to remove them. When an electron is removed from lithium, the remaining electron experiences less shielding and thus a greater attractive force from the nucleus, increasing the ionization energy required to remove it.

How does the distance of an electron from the nucleus affect its ionization energy?

The closer an electron is to the nucleus, the stronger the attractive force it experiences, and thus more energy is required to remove it. This is why the second ionization energy, involving the removal of an electron from the 1s orbital, is much higher than the first.

Why does lithium tend to form a +1 cation rather than a +2 cation?

Lithium tends to form a +1 cation because it requires significantly less energy to remove one electron (520 kJ/mol) than to remove two electrons (7,298 kJ/mol), which would be necessary to form a +2 cation.

Outlines

00:00

🔬 Ionization Energy Comparison: Lithium's First and Second

This paragraph introduces the concept of comparing the first and second ionization energies using lithium as an example. It explains that lithium, with an atomic number of 3, has three electrons matching the number of protons in its nucleus. The electron configuration of a neutral lithium atom is detailed as 1s² 2s¹. The process of ionization is described, where the first ionization energy required to remove the outermost electron is approximately 520 kilojoules per mole, resulting in a lithium ion with a +1 charge and an electron configuration of 1s². The second ionization energy, which is significantly higher at 7,298 kilojoules per mole, is also introduced, leading to a lithium ion with a +2 charge and an electron configuration of 1s¹.

05:01

🔍 Factors Influencing Ionization Energy: Shielding and Distance

The second paragraph delves into the factors that cause the large difference between the first and second ionization energies, focusing on electron shielding and the distance of electrons from the nucleus. It explains that electron shielding, or screening, reduces the effective nuclear charge felt by outer electrons due to the repulsion between inner and outer electrons. The effective nuclear charge for lithium's outermost electron is calculated, showing it feels a significantly reduced charge compared to the actual nuclear charge. The paragraph then contrasts the shielding effect in neutral lithium versus the lithium +1 cation, highlighting the increased attraction and thus higher energy required to remove the second electron. Additionally, the distance of the electrons from the nucleus is discussed, with the inner electron feeling a stronger attractive force due to its proximity, necessitating more energy for removal. This understanding helps explain why lithium tends to form a +1 cation rather than a +2 cation, as the energy required to remove the second electron is substantially higher.

Keywords

💡Ionization Energy

Ionization energy is the energy required to remove an electron from an atom or ion. In the video, it is the central theme, as the script discusses the first and second ionization energies of lithium, explaining that the first ionization energy is the energy needed to remove the outermost electron, while the second ionization energy is significantly higher due to the increased effective nuclear charge and decreased electron shielding.

💡Lithium

Lithium is used as an example in the video to illustrate the concept of ionization energy. It is an alkali metal with an atomic number of 3, meaning it has 3 protons and, in its neutral state, 3 electrons. The script describes lithium's electron configuration and how it forms a +1 cation after losing one electron and a +2 cation after losing two electrons.

💡Electron Configuration

Electron configuration refers to the arrangement of electrons in an atom's orbitals. The video script specifies lithium's electron configuration as 1s2 2s1, indicating two electrons in the 1s orbital and one in the 2s orbital. This configuration is essential for understanding the process of ionization and the changes that occur when electrons are removed.

💡Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by an electron in a shell after accounting for the shielding effect of other electrons. The script explains that for lithium, the effective nuclear charge for the outermost electron is approximately +1, after considering the shielding by the two 1s electrons, which influences the ionization energy.

💡Electron Shielding

Electron shielding, also known as electron screening, is the phenomenon where inner-shell electrons reduce the attractive force exerted by the nucleus on outer-shell electrons. The script uses the concept to explain why the second ionization energy of lithium is much higher than the first, as the second electron experiences less shielding and thus a stronger nuclear attraction.

💡Cation

A cation is an ion with a positive charge, typically formed when an atom loses one or more electrons. The video script describes how lithium becomes a lithium +1 cation after losing one electron and a lithium +2 cation after losing two electrons, which is directly related to the concept of ionization energy.

💡Nuclear Charge

Nuclear charge refers to the total positive charge of an atomic nucleus, which is equal to the number of protons. The script mentions that lithium has a nuclear charge of +3, which is a fundamental factor in determining the atom's ionization energy.

💡First Ionization Energy

First ionization energy is the energy required to remove the most loosely bound electron from a neutral atom. The script states that for lithium, this energy is approximately 520 kilojoules per mole, which is the energy needed to form a lithium +1 cation.

💡Second Ionization Energy

Second ionization energy is the energy required to remove an electron from a cation, specifically from the lithium +1 ion in the script's context. The video explains that this energy is significantly higher, approximately 7,298 kilojoules per mole, due to the lack of electron shielding and the increased effective nuclear charge.

💡Distance from Nucleus

The distance of an electron from the nucleus affects the strength of the electrostatic force between them. The script uses this concept to explain why the second electron is harder to remove from lithium than the first, as the remaining electron in the lithium +1 cation is closer to the nucleus and thus experiences a stronger attractive force.

💡Coulomb's Law

Coulomb's Law describes the electrostatic force between two charged particles, which is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. The script implicitly refers to this law when explaining the increased attractive force experienced by the electron in the lithium +1 cation due to its closer proximity to the nucleus.

Highlights

Introduction of comparing first and second ionization energies using lithium as an example.

Lithium's atomic number is 3, with a neutral atom configuration of 1s2 2s1.

First ionization energy of lithium is approximately 520 kilojoules per mole.

Formation of lithium plus 1 cation upon removal of the outermost electron.

Second ionization energy of lithium is significantly higher at 7,298 kilojoules per mole.

Electron configuration of lithium plus 1 cation is 1s2, losing the 2s orbital electron.

Electron configuration of lithium plus 2 cation is 1s1 after the second ionization.

Significant difference between first and second ionization energies explained.

Importance of nuclear charge in ionization energy, constant in both ionization processes.

Role of electron shielding in reducing the effective nuclear charge felt by outer electrons.

Calculation of effective nuclear charge by subtracting shielding electrons from protons.

Decreased electron shielding in lithium plus 1 cation increases the attraction to the nucleus.

Greater attractive force on the second electron due to less shielding, requiring more energy to remove.

Distance of electrons from the nucleus as a factor in ionization energy, closer electrons are harder to remove.

Coulomb's law applied to explain the increased attractive force on closer electrons.

Practical implications of ionization energy differences in predicting the formation of ions.

Lithium tends to form a plus 1 cation due to the energy required for further ionization.

Transcripts

In the previous videos we've talked about only

the first ionization energy.

In this video, we're going to compare

the first and the second ionization energies,

and we're going to use lithium as our example.

So in the previous video, we already

know that lithium has an atomic number of 3,

so there are three protons in the nucleus.

In a neutral atom of lithium, the number of electrons

equals the number of protons, and so we

know there are three electrons in lithium here.

The electron configuration is 1s2 2s1.

So we have two electrons in the 1s orbital

so we can go ahead and put those two

electrons in the 1s orbital like that.

And then we have one more electron,

and that electron's going to go into the 2s orbital like this.

And so that would be a very simple picture

of the neutral lithium atom.

If we apply enough energy, we can actually

pull away this outer electron here.

So we can pull away that electron,

and we call this the first ionization energy.

And to pull away that electron takes

approximately 520 kilojoules per mole.

And so once we've pulled that electron away,

we no longer have a neutral lithium atom, right?

We would have a lithium ion because we would still

have three positive charges in the nucleus,

but we have only two negative charges now.

We only have two electrons because we pulled one away.

So 3 minus 2 gives us plus 1.

So this is the lithium plus 1 cation.

And the electron configuration would just

be 1s2 because we lost the electron in the 2s orbital.

And so we could keep going.

We could apply some more energy and pull away another electron.

So let's say that we pull away this electron this time.

OK, so we're taking a second electron away,

and so we wouldn't call this ionization energy 1.

We would therefore call this ionization energy 2

because this is to take away the second electron.

And this value turns out to be approximately 7,298 kilojoules

per mole.

And so if we take away that second electron, once again

we still have three positive charges in the nucleus,

but we have only one negative charge now.

There's only one electron so this is no longer

the lithium plus 1 cation.

This is the lithium plus 2 cation because 3 minus 1

is plus 2.

So this is lithium plus 2 here, and the electron configuration

would be only one electron in a 1s orbital, so 1s1.

So we can see that there is a big difference

between the first ionization energy

and the second ionization energy, so 520 versus 7,298.

So let's see if we can explain the reasoning

for this extremely large difference in ionization

energies.

And we're going to use the three factors that we've

talked about in the previous videos.

So the first factor we discussed was nuclear charge,

which refers to the number of protons in the nucleus.

So if we look at the neutral lithium atom,

three positive charges in the nucleus.

That positive charge is what's going

to attract this electron in magenta here.

And if we look at the lithium plus 1

cation, similar situation.

We still have three protons in the nucleus,

and so that positive charge is what's

going to be attracting this electron as well.

And so because of the same number of protons,

we have to think more about effective nuclear charge, as

opposed to how many protons there are in the nucleus.

And before we do that, we have to consider

the effect of electron shielding.

So let's talk about electron shielding next.

So electron shielding, also called electron screening,

so electron shielding slash screening.

So when we think about electron shielding,

we're thinking about the inner orbital electrons here.

So going back to the neutral lithium atom,

these two inner shell electrons right here

are going to repel this outer shell electron.

So this one is going to repel this one as well.

And so we can think about it as they screen the electron

in magenta from feeling the full force of the positive 3 charge

in the nucleus because electrons repel other electrons.

And so the way to calculate the effect of nuclear charge--

so we've done this in the previous videos

as well-- the simple way of calculating

effective nuclear charge is take the number of protons,

so plus 3, and from that you subtract

the number of shielding electrons.

So in this case, it would be these two electrons

in the 1s orbital.

So 3 minus 2 gives us an effective nuclear charge

of plus 1.

And so the electron in magenta isn't

feeling a nuclear charge of plus 3.

It's really only feeling an effective nuclear charge close

to positive 1 because the actual value is approximately 1.3

when you do the more complicated calculations.

And so the effect of electron shielding

is to decrease the overall nuclear charge

that this electron magenta feels.

And so when we move over here to this electron,

so I'm talking about this electron in magenta

for the lithium plus 1 cation, it's

not the same situation, right?

There's not much electron shielding.

This electron over here might repel it a little bit,

but there are no inner shell electrons

repelling this electron in magenta.

And because of that, the electron in magenta

is going to feel this positive 3 charge, much

more of the full positive 3 charge of the nucleus.

And so therefore, there's going to be

a much greater attractive force holding

this electron in magenta to this nucleus.

And therefore, you have to apply more energy

to pull that electron away.

So the effect of electron shielding

tells you the second electron is much harder

to remove than the first, and so we

see a large increase in ionization energy

from the first ionization energy to the second ionization

energy.

The last factor that we discussed was distance,

so the distance of those electrons in magenta

from the nucleus.

So on the left, once again going back to the neutral lithium

atom, this electron is in the second energy level.

So it's further away than this electron.

This electron is in the first energy level, in the 1s2,

so this distance here is smaller than the distance on the left.

And so since the distance is smaller,

this electron in magenta feels more

of an attractive force from the nucleus.

Once again, that's Coulomb's law.

And so therefore, there's an increased attractive force.

Therefore, you take more energy to pull that electron away.

So it takes much more energy to pull the second electron

away than the first, and so that's

why we see an increase in ionization energy.

So distance says the fact that this electron is closer

means it takes more energy to pull it away,

and that's another reason why this number

for the second ionization energy is

so much larger than the first.

So it takes a heck of lot more energy

to pull away your second electron.

And that explains why we see lithium forming a plus 1

cation, because it doesn't take anywhere near as much energy

to pull away one electron as it does to take away two

to form a lithium 2 plus.

And so this is one way to tell what kind of an ion will form.

Look at the ionization energies, and when you see a huge jump,

that clues you in as to which ions are easier to form.