What is electron affinity? | Chemistry | Extraclass.com

Summary

This video explains the concept of electron affinity, which is the energy change when a neutral atom gains an electron, forming a negative ion. It covers the first and second electron affinities, with examples like oxygen, and highlights factors that affect electron affinity, including nuclear charge, atomic size, electronic configuration, and shielding effects. The video also discusses periodic trends, showing that electron affinity generally increases across a period and decreases down a group, with notable exceptions such as nitrogen and fluorine. By understanding these concepts, viewers gain insight into how atoms interact with electrons and why some elements more readily accept electrons than others.

Takeaways

• 😀 Electron affinity is the energy change when a neutral atom in the gas phase gains an electron and releases energy.
• 😀 Higher electron affinity indicates a stronger tendency of an atom to accept electrons.
• 😀 When an atom gains an electron, it forms a negative ion, and energy is released (exothermic process).
• 😀 There are two types of electron affinity: first electron affinity (neutral atom) and second electron affinity (negative ion).
• 😀 Second electron affinity is positive because adding an electron to a negative ion requires energy.
• 😀 Electron affinity is influenced by factors such as nuclear charge, atomic size, shielding effect, and electronic configuration.
• 😀 Smaller atoms with higher nuclear charge have higher electron affinity due to stronger attraction on incoming electrons.
• 😀 Atoms with stable electronic configurations (full or half-filled orbitals) resist gaining electrons, resulting in lower electron affinity.
• 😀 Across a period in the periodic table, electron affinity generally increases from left to right, with some exceptions like carbon and nitrogen.
• 😀 Down a group in the periodic table, electron affinity generally decreases, though exceptions exist, such as chlorine having slightly higher EA than fluorine.
• 😀 Electron affinity is most relevant for elements in groups 16 and 17 and is considered the negative-ion equivalent of ionization energy.

Q & A

What is electron affinity?

Electron affinity is the change in energy that occurs when a neutral atom in the gas phase gains an electron, releasing energy in the process.

Why is electron affinity considered a measure of an atom's likelihood to gain an electron?

Because electron affinity indicates how easily a neutral atom can accept an electron. A higher electron affinity means the atom more readily gains an electron.

What happens to a neutral atom when it gains an electron?

When a neutral atom gains an electron, it becomes a negative ion, also called an anion.

What is the difference between first and second electron affinity?

First electron affinity is the energy released when an electron is added to a neutral atom. Second electron affinity is the energy released when an electron is added to a negative ion, and it is usually positive because adding an electron to an already negatively charged ion requires extra energy.

Why is the first electron affinity of oxygen negative while the second is positive?

The first electron affinity of oxygen is negative (−142 kJ/mol) because energy is released when a neutral atom gains an electron. The second electron affinity is positive (+844 kJ/mol) because adding an electron to a negatively charged ion requires energy input due to repulsion.

What factors affect electron affinity?

Electron affinity depends on nuclear charge, atomic size, shielding effect, and electronic configuration. Higher nuclear charge increases EA, larger atomic size decreases EA, stronger shielding decreases EA, and atoms with stable electron configurations resist gaining electrons.

How does nuclear charge influence electron affinity?

A higher nuclear charge means more protons in the nucleus, which exert a stronger attractive force on incoming electrons, resulting in higher electron affinity.

What is the general trend of electron affinity across a period and down a group in the periodic table?

Across a period (left to right), electron affinity generally increases due to higher nuclear charge and smaller atomic size. Down a group, electron affinity generally decreases because atomic size increases, reducing the attraction for incoming electrons.

What are the notable exceptions to the periodic trends of electron affinity?

In a period, carbon has a higher electron affinity than nitrogen due to nitrogen's stable half-filled valence shell. In a group, fluorine has slightly lower electron affinity than chlorine due to its very small size and high electron density.

Why do atoms with stable electronic configurations have lower electron affinity?

Atoms with fully filled or half-filled orbitals (like p⁶, d¹⁰, f¹⁴, or p³, d⁵, f⁷) are more stable and resist gaining additional electrons, making it more difficult to add an electron, resulting in lower electron affinity.

How is electron affinity related to ionization energy?

Electron affinity is conceptually the negative-ion equivalent of ionization energy. While ionization energy measures the energy required to remove electrons (forming positive ions), electron affinity measures the energy released when an atom gains electrons (forming negative ions).