A Level Chemistry Revision "Ionisation Energy across a Period"

Summary

This video from Three Science explores the variation of first ionization energy across a period in the periodic table. It explains that ionization energy generally increases with atomic number due to greater nuclear charge and decreased atomic radius. Exceptions occur with boron and oxygen, where subshell electron configurations and electron-electron repulsion in the 2p subshell lead to lower ionization energies. The video also briefly touches on similar patterns in period 3, providing a clear understanding of this fundamental concept in chemistry.

Takeaways

• 🔬 The first ionization energy generally increases as you move across a period in the periodic table due to the increasing nuclear charge and decreasing atomic radius.
• 📈 A plot of the first ionization energy against atomic number shows a trend of increase, with exceptions in period two for nitrogen and oxygen.
• 💡 The overall increase in ionization energy is attributed to the stronger attraction between the nucleus and the electrons as you move across a period.
• 🌐 The atomic radius decreases across a period, which also contributes to the increased ionization energy.
• 🚫 Electrons are removed from the same electron shell (the second shell in period two), meaning the shielding effect is similar for each element.
• 🚀 Exceptions to the increasing trend are seen with boron and oxygen in period two, which have lower first ionization energies due to their electron configurations.
• 🌀 The 2p sub-shell has a higher energy than the 2s sub-shell, which explains why boron has a lower first ionization energy than beryllium.
• 🔄 Electron repulsion within the 2p sub-shell of oxygen results in a lower first ionization energy compared to nitrogen, where electrons occupy separate orbitals.
• 📊 A similar pattern of ionization energy increase with exceptions is observed in period three, involving the third energy level.
• 🛑 The first ionization energy decreases when moving from magnesium to aluminum and from phosphorus to sulfur in period three, due to electron configurations and orbital energies.
• 📚 Understanding the variations in first ionization energy across periods is crucial for grasping the chemical properties and reactivity of elements.

Q & A

What does the video aim to teach viewers about ionization energy?

The video aims to teach viewers how the first ionization energy varies across a period in the periodic table of elements.

How does the first ionization energy generally change as we move across a period?

The first ionization energy generally increases as we move across a period due to the increase in nuclear charge and the decrease in atomic radius.

What causes the atomic radius to decrease across a period?

The atomic radius decreases across a period because of the increasing nuclear charge which pulls the electrons closer to the nucleus.

Why does the first ionization energy of boron differ from the expected pattern?

The first ionization energy of boron is lower than expected because the outer electron is in the 2p sub-shell, which has a higher energy and thus requires less energy to remove compared to the 2s sub-shell of beryllium.

What is the electron configuration difference between nitrogen and oxygen that affects their ionization energies?

In nitrogen, each electron in the 2p sub-shell is in a separate orbital, whereas in oxygen, one of the 2p orbitals contains a pair of electrons. The repulsion between these paired electrons in oxygen makes it easier to remove one electron, resulting in a lower first ionization energy compared to nitrogen.

What is the shielding effect mentioned in the script, and how does it relate to ionization energy?

The shielding effect refers to the decrease in the effective nuclear charge experienced by the outer electrons due to the presence of inner electrons. It affects ionization energy as it influences how strongly the outer electrons are attracted to the nucleus.

Why does the first ionization energy decrease when going from magnesium to aluminum in period 3?

The decrease in first ionization energy from magnesium to aluminum in period 3 is due to the electron configuration and the energy levels of the 3p sub-shell, similar to the pattern observed in period 2 with boron and beryllium.

What is the significance of the first ionization energy in understanding the reactivity of elements?

The first ionization energy is significant in understanding the reactivity of elements because it indicates the energy required to remove an electron. Elements with higher ionization energies are generally less reactive, while those with lower ionization energies are more reactive.

How does the video script explain the exceptions to the increasing trend of ionization energy across a period?

The script explains the exceptions by examining the electron configurations and sub-shells involved, particularly focusing on the energy levels of the sub-shells and the effects of electron-electron repulsion in certain elements like nitrogen and oxygen.

What is the Bohr model mentioned in the script, and how does it relate to ionization energy?

The Bohr model is a simplified model of the atom where electrons orbit the nucleus in distinct energy levels or shells. It relates to ionization energy as it helps explain why certain elements have lower ionization energies due to the higher energy of their outer electrons in certain sub-shells.