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.