Question

The electronic configurations of some elements are given below. The element with highest electron affinity is: (a) \(1 s^{2}, 2 s^{2}, 2 p^{3}\) (b) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{4}\) (c) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{5}\) (d) \(1 \mathrm{~s}^{2}, 2 \mathrm{~s}^{2}, 2 \mathrm{p}^{2}\)

Short answer

Option (c) with configuration \(1s^2, 2s^2, 2p^5\) has the highest electron affinity.

Step-by-step solution

Understanding Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gaseous state to form a negative ion. Generally, elements with higher electron affinity are more likely to attract and gain an additional electron.

Recognize the Elements by Their Configuration

Identify each element from its electron configuration: (a) \(1s^2, 2s^2, 2p^3\) corresponds to Nitrogen (N), (b) \(1s^2, 2s^2, 2p^4\) corresponds to Oxygen (O), (c) \(1s^2, 2s^2, 2p^5\) corresponds to Fluorine (F), (d) \(1s^2, 2s^2, 2p^2\) corresponds to Carbon (C).

Compare Electron Affinities

Among the given configurations, Fluorine (\(1s^2, 2s^2, 2p^5\)) has the highest electron affinity because it is one electron short of having a complete outer shell, which makes it very eager to gain an electron.

Conclusion using Trends

Electron affinity typically increases across a period (left to right across a row in the periodic table) as the elements become more eager to complete their electron shell. Fluorine, being the right-most in the 2nd period among the provided options, will have the highest electron affinity.

Key concepts

Electronic Configuration

Electronic configuration is a way of expressing how electrons are distributed among the various atomic orbitals of an atom. This arrangement is important because it determines how an atom interacts with others chemically. Electrons fill orbitals in a specific order, starting with the lowest energy level. This is guided by the Aufbau principle, which details the sequence in which electron orbitals are filled:

• Electrons fill orbitals in the order of increasing energy: 1s, 2s, 2p, 3s, and so on.
• Each orbital can hold a maximum of two electrons, which must have opposite spins (Pauli exclusion principle).
• Electrons will singly occupy orbitals of the same energy before pairing up in any given orbital (Hund's rule).

For instance, the electronic configuration for Fluorine (\(1s^2, 2s^2, 2p^5\)) shows that it has a total of nine electrons. The configuration tells us that Fluorine has its first energy level completely filled, and it requires only one more electron to fill its second energy level's p orbital.

Periodic Trends

Periodic trends are patterns that emerge within the periodic table as you move across periods or down groups. These trends help us understand the behavior of different elements. One key trend is electron affinity, which generally increases across a period from left to right. This is due to the increase in nuclear charge, meaning more protons attract the electrons in the outer shell more strongly. Another important trend is the decrease in atomic size across a period, causing the electrons to be held more tightly. As you move down a group, electron affinity typically decreases because the added electron is entering an orbital farther away from the nucleus and thus less tightly bound. These trends highlight why elements on the far right such as Fluorine tend to have high electron affinities—they eagerly attract and gain electrons to achieve stable electronic configurations.

Fluorine

Fluorine is a highly reactive non-metal and belongs to the halogens group in the periodic table. With an electronic configuration of \(1s^2, 2s^2, 2p^5\), Fluorine is just one electron short of having a complete outer electron shell.Due to this near-complete level, Fluorine exhibits a strong desire to gain an extra electron, accounting for its highest electron affinity among the elements in the second period. This characteristic makes Fluorine extremely reactive and capable of forming stable bonds by accepting electrons from other elements.The high electron affinity of Fluorine is also explained by its high electronegativity, the ability of an atom to attract electrons within a bond. Its small atomic radius allows Fluorine to exert a strong attractive force on electrons, making it one of the most electronegative elements in the periodic table. This makes Fluorine highly effective in forming ionic and covalent bonds, completing its valence shell and achieving stability.