A Level Chemistry Revision "Ionisation Energy across a Period"

Freesciencelessons

3 May 202003:36

Summary

TLDRThis 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.

Outlines

00:00

🔬 Ionization Energy Trends Across a Period

This paragraph introduces the concept of ionization energy and its variation across a period in the periodic table. The script explains that the first ionization energy generally increases as you move from left to right across a period due to the increasing nuclear charge and decreasing atomic radius, which enhances the attraction between the nucleus and the electrons. However, there are exceptions in period two, specifically between boron and oxygen, and nitrogen and oxygen, which will be discussed in subsequent sections.

📉 Exceptions to the Ionization Energy Increase

This section delves into the exceptions to the general increase in first ionization energy across a period. It discusses the electron configurations of period 2 elements, highlighting the difference in energy levels between the 2s and 2p sub-shells. The lower ionization energy of boron compared to beryllium is attributed to the 2p sub-shell's higher energy, requiring less energy to remove an electron. The decrease in ionization energy from nitrogen to oxygen is explained by the electron-electron repulsion in the 2p orbitals of oxygen, where a pair of electrons occupies one orbital, making it easier to remove one electron.

Mindmap

Keywords

💡Ionization Energy

Ionization energy refers to the energy required to remove an electron from an atom or molecule. In the context of the video, it is the focus of the discussion on how this energy changes across a period in the periodic table. The video explains that ionization energy generally increases across a period due to the increasing nuclear charge and decreasing atomic radius, which makes the outer electrons more attracted to the nucleus.

💡Period

A period in the periodic table refers to a horizontal row of elements. The video script discusses how the first ionization energy varies across a period, highlighting the general trend of increasing ionization energy and the exceptions to this trend, such as the decrease from nitrogen to oxygen in period two.

💡Atomic Number

The atomic number is the number of protons in the nucleus of an atom, which determines the element's identity. The video uses atomic number to plot the first ionization energy, showing the relationship between the number of protons and the energy required to remove an electron.

💡Nuclear Charge

Nuclear charge is the total positive charge of an atom's nucleus, which is determined by the number of protons. The video explains that as one moves across a period, the nuclear charge increases, leading to a stronger attraction between the nucleus and the electrons, which in turn increases the ionization energy.

💡Atomic Radius

Atomic radius is the distance from the nucleus to the outermost electron(s) of an atom. The video script mentions that atomic radius decreases across a period, contributing to the increased ionization energy as the outer electrons are pulled closer to the nucleus.

💡Electron Shell

An electron shell is a region in an atom where electrons are located. The video discusses how the first ionization energy is affected by electrons in the same electron shell, specifically the second electron shell in the case of period two elements.

💡Shielding Effect

The shielding effect is the reduction of the nuclear charge's attraction on outer electrons due to the presence of inner electron shells. The video script explains that the shielding effect is similar for each element within a period, as the electrons being removed are from the same shell.

💡Subshells

Subshells are subdivisions of electron shells, designated by letters (s, p, d, f). The video highlights the role of subshells in explaining exceptions to the trend of increasing ionization energy, such as the lower ionization energy of boron compared to beryllium due to the 2p subshell having a higher energy than the 2s subshell.

💡Orbitals

Orbitals are regions within subshells where electrons are most likely to be found. The video uses the example of oxygen to explain how electrons in the same orbital of the 2p subshell repel each other, which affects the ionization energy and leads to a decrease in ionization energy from nitrogen to oxygen.

💡Electron Configuration

Electron configuration describes the distribution of electrons in an atom's subshells. The video script uses electron configurations to explain the variations in ionization energy across a period, particularly focusing on the differences in subshells and orbitals occupied by the valence electrons.

Highlights

The first ionization energy generally increases as we move across a period due to increasing nuclear charge and decreasing atomic radius.

In period two, the first ionization energy decreases when going from nitrogen to oxygen, which is an exception to the general trend.

The increased nuclear charge and decreased atomic radius cause outer electrons to be more attracted to the nucleus, leading to an increase in ionization energy.

All elements in the discussion remove an electron from the same electron shell, which is the second shell in this case.

The shielding effect due to the inner electron shell is similar for each element, influencing ionization energy.

Boron and oxygen do not follow the pattern of increasing first ionization energy and require a deeper look into subshells.

The 2p sub-shell has a higher energy than the 2s subshell, which affects the ionization energy of boron compared to beryllium.

Oxygen's first ionization energy is less than nitrogen's due to electron repulsion in the 2p sub-shell.

In period 3, similar exceptions to the increasing ionization energy trend are observed with magnesium to aluminum and phosphorus to sulfur.

The third energy level in period 3 is considered for ionization energy analysis, differing from the second energy level in period 2.

Electron configurations play a crucial role in understanding variations in first ionization energy across periods.

The video explains the concept of electron shielding and its impact on ionization energy.

The Bohr model is referenced to explain why certain elements have lower first ionization energies.

The video provides a detailed analysis of the electron configurations of period 2 elements.

The significance of electron repulsion in orbitals is highlighted as a reason for variations in ionization energy.

The video concludes with a summary of how first ionization energy varies across a period, reinforcing the learned concepts.

The educational content is structured to progressively build understanding of ionization energy trends and exceptions.

Visual aids such as graphs and electron configuration diagrams are utilized to enhance comprehension.