Question

Which element in the following pairs is likely to gain an electron more easily? (a) \(\mathrm{H}\) or \(\mathrm{He}\) (b) \(\mathrm{S}\) or \(\mathrm{Si}\) (c) \(\mathrm{Cr}\) or \(\mathrm{Mn}\)

Short answer

(a) H, (b) S, (c) Mn

Step-by-step solution

Understanding the Concept

An element's ability to gain an electron is closely related to its 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. The higher the electron affinity, the more likely an element is to gain an electron. Generally, nonmetals have higher electron affinities than metals, and within the same period, electron affinity increases from left to right.

Comparing Hydrogen and Helium

Hydrogen ( abla ext{H} abla) is a nonmetal with one electron, while helium ( abla ext{He} abla) is a noble gas with a full valence shell. Hydrogen, with just one electron, can easily gain an electron to form a stable abla ext{H}^- abla ion. Helium is already stable with a complete outer shell (two electrons) and does not tend to gain more electrons. Therefore, hydrogen is more likely to gain an electron than helium.

Comparing Sulfur and Silicon

Sulfur ( abla ext{S} abla) and silicon ( abla ext{Si} abla) are both in the same period, but sulfur is a nonmetal, while silicon is a metalloid. Nonmetals generally have a higher tendency to gain electrons compared to metalloids and metals. Hence, sulfur, having higher electron affinity as a nonmetal, is more likely to gain an electron compared to silicon.

Comparing Chromium and Manganese

Chromium ( abla ext{Cr} abla) and manganese ( abla ext{Mn} abla) are both transition metals. Transition metals do not have a significant tendency to gain electrons as compared to nonmetals. However, of these two, manganese has a slightly higher electron affinity than chromium, which makes it marginally more likely to gain an electron.

Key concepts

Nonmetals

Nonmetals are elements that are typically found on the right side of the periodic table, excluding noble gases. These elements have high electron affinities, meaning they easily gain electrons to form negative ions.
Nonmetals like oxygen, nitrogen, and sulfur possess this characteristic. Their high electron affinity is due to their strong need to fill their outer electron shells and achieve stability, as described by the octet rule.

• Nonmetals have higher ionization energies.
• They act as good oxidizing agents.
• In chemical reactions, they tend to acquire electrons rather than lose them.

Because of these properties, nonmetals usually form negative ions. The tendency of nonmetals to gain electrons makes them highly important in various chemical processes, including combustion and respiration.

Transition Metals

Transition metals are located in the center of the periodic table. They are characterized by partially filled d or f electron subshells. Unlike nonmetals, transition metals generally exhibit lower tendencies to gain additional electrons. Their electron configuration allows them to form various oxidation states, facilitating different types of chemical bonding.
The moderate electron affinity of transition metals enables them to form compounds where they may donate, accept, or share electrons, often acting as catalysts. Manganese and chromium are examples of such elements with multiple oxidation numbers.

• Transition metals often create alloys due to their versatile electron configurations.
• They display magnetic and conductive properties, making them valuable in technology and industry.
• Their tendency to form colored compounds is used in inks and paints.

Thus, even though they don’t gain electrons as readily as nonmetals, the unique electronic structure of transition metals is crucial for diverse chemical applications.

Electron Gain Tendency

The electron gain tendency refers to how likely an atom is to accept an additional electron. This tendency is influenced by several factors, including the element’s electron affinity, atomic size, and its position on the periodic table.
Elements with high electron affinities are more likely to gain electrons. The general trends are:

• Nonmetals, especially halogens, have high electron gain tendencies.
• Electron affinity increases across a period and decreases down a group.
• Noble gases have low electron gain tendencies due to their complete valence shells.

Such tendencies affect reactivity, with elements more likely to gain electrons participating readily in reactions to form negative ions.
Understanding electron gain tendencies helps predict an element's behavior in chemical reactions and is essential in designing industrial chemical processes, such as the production of semiconductors and pharmaceuticals.