Afinitas Elektron dan Penyimpangan Energi Afinitas Elektron

Summary

This video discusses electron affinity, which refers to the energy change when an electron is added to an atom or ion in its gaseous state. The video explains the difference between negative and positive electron affinity values, indicating whether energy is released (exothermic) or absorbed (endothermic) during electron capture. It highlights trends across groups in the periodic table, focusing on Group 7A elements, and also addresses anomalies in electron affinity for noble gases, alkaline earth metals, and nitrogen. The video concludes with a review of these concepts, aiming to clarify how electron affinity varies based on atomic structure and position in the periodic table.

Takeaways

• 😀 Electron affinity refers to the energy change when an electron is added to an atom or ion in the gas phase.
• 😀 Generally, atoms release energy when the first electron is added, and this process is usually exothermic (negative electron affinity).
• 😀 A positive electron affinity means energy is required to add an electron, indicating an endothermic process.
• 😀 The electron affinity of chlorine is an example where it releases 349 kJ/mol of energy when it gains an electron to form Cl-.
• 😀 The first electron affinity is generally negative, but the second electron affinity is always positive, indicating that adding another electron requires energy.
• 😀 The second electron affinity of oxygen, for instance, requires 843 kJ/mol of energy to form O2-.
• 😀 Electron affinity varies across groups: for Group 7A elements (halogens), electron affinity is more negative (releases more energy).
• 😀 Group 1A elements (alkali metals) show increasing positive electron affinity as you move down the group.
• 😀 The electron affinity of noble gases is positive because their stable electron configurations resist adding extra electrons.
• 😀 Elements like nitrogen, beryllium, and magnesium also have positive electron affinities due to electron-electron repulsion when adding an electron to already filled orbitals.

Q & A

What is electron affinity?

Electron affinity is the energy change that occurs when an electron is added to a neutral atom or ion in the gas phase. It can either release energy (negative value) or require energy (positive value) depending on the atom's ability to attract the electron.

What does a negative electron affinity indicate?

A negative electron affinity indicates that the atom releases energy when it gains an electron, meaning the process is exothermic.

What does a positive electron affinity indicate?

A positive electron affinity indicates that the atom requires energy to accept an electron, meaning the process is endothermic.

Why do halogens like chlorine have high negative electron affinities?

Halogens have high negative electron affinities because they are one electron short of achieving a stable noble gas configuration. When they gain an electron, they release energy as they complete their outer shell.

How does electron affinity vary across groups in the periodic table?

In general, as you move from left to right across a period, electron affinity becomes more negative, meaning atoms are more likely to release energy when gaining an electron. In groups like alkali metals (Group 1A), the trend is less consistent.

Why does oxygen have a positive electron affinity for its second electron?

The second electron added to oxygen experiences electrostatic repulsion from the already existing electrons in the atom. This repulsion makes it energetically unfavorable, requiring energy to force the second electron into the atom.

What is the general trend for electron affinity as you move down a group?

As you move down a group in the periodic table, electron affinity tends to become less negative, meaning it becomes less exothermic or more endothermic, as the atom’s size increases and its ability to attract electrons decreases.

Why do noble gases have positive electron affinities?

Noble gases have positive electron affinities because their electron configurations are already stable. Adding an electron would force it into a higher energy orbital, which is energetically unfavorable and requires energy.

How does the electron affinity of nitrogen differ from other elements in its group?

Nitrogen has a positive electron affinity because the addition of an electron forces it into an already half-filled 2p orbital, resulting in electron-electron repulsion. This repulsion makes it energetically unfavorable to add the electron.

What causes the exceptions in electron affinity, such as for noble gases and nitrogen?

Exceptions in electron affinity arise due to electron-electron repulsion in cases like nitrogen, where adding an electron forces it into an already half-filled orbital. For noble gases, the stable electron configuration makes it energetically unfavorable to add an electron.