Problem 17 - Chemistry in 30 days

Question

Which of the following will have maximum electron affinity ? (a) \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{5}\) (b) \(\mathrm{ls}^{2} 2 \mathrm{~s}^{2} 2 p^{6}\) (c) \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 p^{6} 3 \mathrm{~s}^{2} 3 \mathrm{p}^{5}\) (d) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6}\)

Step-by-Step Solution

Answer

Chlorine (Option c) has the maximum electron affinity.

Step 1: Understanding Electron Configuration

To solve this problem, we need to understand the electron configurations given in the options. They represent the distribution of electrons in an atom's shells and subshells.

Step 2: Analyzing Option A

The electron configuration (a) is given as \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{5}\), which corresponds to Fluorine (F). The atomic number for fluorine is 9.

Step 3: Analyzing Option B

The electron configuration (b) is \(1\mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 p^{6}\), which matches the configuration of Neon (Ne), a noble gas with an atomic number of 10.

Step 4: Analyzing Option C

The electron configuration (c) is \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 p^{6} 3 \mathrm{~s}^{2} 3 \mathrm{p}^{5}\), which corresponds to Chlorine (Cl). The atomic number for chlorine is 17.

Step 5: Analyzing Option D

The electron configuration (d) is \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6}\), which matches Argon (Ar), another noble gas with an atomic number of 18.

Step 6: Understanding Electron Affinity

Electron affinity measures how easily an atom can accept an additional electron, with nonmetals typically having higher affinities than metals or noble gases. Fluorine and chlorine are known for high electron affinities.

Step 7: Comparing Non-Noble Gases

Between Fluorine (option a) and Chlorine (option c), both are nonmetals with high electron affinities. However, Chlorine usually has a slightly higher electron affinity than Fluorine due to less electron-electron repulsion in the larger outer shell.

Key Concepts

Electron Configuration

Electron configuration is the arrangement of electrons in the orbitals of an atom. It helps us understand how the electrons occupy the different energy levels (or shells) in an atom. Each level can contain a specific number of electrons, distributed in subshells labeled as s, p, d, and f. An atom's configuration reveals not only its reactivity but also its magnetic properties.

• The s subshell can hold 2 electrons.
• The p subshell can hold 6 electrons.
• The d subshell can hold 10 electrons, while the f subshell holds 14 electrons.

For example, the electron configuration of Fluorine is given by \(\mathrm{1s^2\; 2s^2\; 2p^5}\), indicating it has electrons in both the first and second energy levels, with a nearly filled p subshell in the second level. Understanding electron configuration is crucial to foresee how elements behave in bonding and chemical reactions.

Nonmetals

Nonmetals are elements found on the right side of the periodic table, known for their high electronegativity and electron affinity. They tend to gain electrons during chemical reactions to achieve a full outer shell, mimicking the stable electron configuration of noble gases. This characteristic is why nonmetals often have higher electron affinities than metals. Some key features of nonmetals include:

• High electron affinities, making them eager to gain additional electrons.
• They are usually poor conductors of electricity and heat.
• Nonmetals can form both ionic and covalent bonds.

Chlorine and Fluorine, both considered in this context, are famous nonmetals due to their high electron affinities. This property allows them to effectively attract electrons from other elements during bonds, making them very reactive.

Noble Gases

Noble gases are a special group of elements found in Group 18 of the periodic table. They include helium (He), neon (Ne), argon (Ar), among others. One of their defining characteristics is a complete set of electrons in their outer shell, making them highly stable and largely unreactive.Noble gases have some distinct traits:

• They have full electron configurations, giving them no tendency to gain, lose, or share electrons.
• These gases are colorless, odorless, and tasteless.
• Due to their stability, they have very low chemical reactivity compared to nonmetals.

For instance, Neon and Argon from the exercise are noble gases, exhibiting full valence shells (\(\mathrm{2s^2\; 2p^6}\) for neon and \(\mathrm{3s^2\; 3p^6}\) for argon), which keep them from participating in chemical reactions readily. Their low electron affinity further emphasizes this stability.

Electron-Electron Repulsion

Electron-electron repulsion is a significant factor in understanding the electron affinities of different elements. It stems from the principle that like charges repel each other. In larger atoms, where additional electrons are added to already populated orbital spaces, repulsion among electrons increases. This phenomenon impacts the electron affinity of elements:

• In small atoms like Fluorine, added electrons face higher repulsions because the space in their p orbitals is more cramped following the atom's compact nature.
• Larger atoms like Chlorine have more space in their outer shell, reducing the repulsion among electrons when a new electron is added.
• This reduced repulsion is why Chlorine usually exhibits a higher electron affinity than Fluorine, despite having more electrons.

In essence, balancing electron-electron repulsion is crucial in determining how strongly an atom will attract additional electrons, affecting its electron affinity. It plays a key role in why elements with larger atomic radii might still show keen electron gain despite ostensibly higher shielding effects.