Question

The electron affinity of \(\mathrm{Be}\) is similar to (a) He (b) B (c) \(\mathrm{Li}\) (d) \(\mathrm{Na}\)

Short answer

(c) \(\mathrm{Li}\)

Step-by-step solution

Understanding Electron Affinity

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state. Atoms with higher electron affinity release more energy when they gain an electron.

Identify Trends in the Periodic Table

In general, electron affinity increases across a period from left to right and decreases down a group. However, there are exceptions due to electron configurations.

Consider Beryllium's Electron Configuration

Beryllium (Be) has an electron configuration of \(1s^2 2s^2\). It has a full 2s orbital, making it less likely to gain an additional electron. Atoms with filled or half-filled sublevels often have lower electron affinities due to their stability.

Analyze the Options

(a) Helium (He): Noble gases typically have very low or negative electron affinities because they have a complete outer shell. (b) Boron (B): Has a higher electron affinity than Be because it needs one more electron to complete the p orbital. (c) Lithium (Li): Has a lower electron affinity than B but similar to Be because it only has one electron in its outer s orbital. (d) Sodium (Na): Has a lower electron affinity as it tries to fill the next s orbital.

Compare Electron Affinities

Be has low electron affinity similar to Li because both have only electrons in the s orbitals and face similar energy releases due to electron configurations. Thus, Be's electron affinity is more comparable to Li's.

Key concepts

Beryllium Electron Configuration

Beryllium, represented as Be on the periodic table, is the fourth element and has the atomic number 4. In simple terms, its electron configuration describes how its electrons are distributed in its atomic orbitals. Beryllium's electron configuration is written as \(1s^2 2s^2\). This tells us two key things:

• The first two electrons fill the \(1s\) orbital.
• The next two electrons fill the \(2s\) orbital, making it full.

Understanding this configuration is important because it helps explain why beryllium has a low electron affinity. Since its outer \(2s\) orbital is completely filled, there is less attraction for an additional electron. The filled \(2s\) orbital makes beryllium's energy state stable, meaning it doesn't easily change or release energy by gaining another electron.

Periodic Table Trends

When we talk about periodic table trends, we refer to patterns seen within the periodic table that help predict and explain the behavior of elements. One such trend is electron affinity, which generally increases across a period from left to right and decreases down a column or group. However, beryllium is an exception to this rule.

• As you move right across a period, elements typically tend to gain electrons to fill their outer shells, increasing electron affinity. But, beryllium with its stable \(2s^2\) configuration doesn’t follow this pattern.
• Going down a group, elements tend to have larger atoms with electrons farther from the nucleus, leading to lower electron affinity due to reduced attraction.

In beryllium’s case, its electron affinity is both low and similar to lithium, which has a partially filled \(2s\) orbital but like Be, finds stability with a filled \(1s\) and partially stable \(2s\) configuration.

Electron Configuration Stability

Electron configuration stability is a concept that explains why certain elements are less likely to gain or lose electrons. This stability is often due to having filled or half-filled outer electron shells. A filled \(s\) or \(p\) orbital contributes to an element's resistance to gaining new electrons.

• For beryllium, the \(1s^2 2s^2\) configuration means it has a completely filled \(2s\) orbital. The filled orbital is stable and does not readily attract additional electrons.
• In contrast, elements with unfilled outer orbitals tend to have higher electron affinities as they strive to complete their electron shells.

This stability helps explain why beryllium's electron affinity is low. The energy benefit of gaining an additional electron does not outweigh the stability of having a filled outer shell. This is a critical reason why its electron affinity is more similar to that of lithium, another element with a low electron affinity.