Problem 187 - A Complete Resource Book in Chemistry for JEE Main

Question

Due to the presence of an unpaired electron, free radicals are (a) chemically reactive (b) chemically inactive (c) anions (d) cations

Step-by-Step Solution

Answer

(a) chemically reactive

Step 1: Understanding Free Radicals

Free radicals are atoms or molecules that have an unpaired electron in their outermost shell. The presence of this unpaired electron gives these species certain chemical properties.

Step 2: Identifying Chemical Reactivity

Due to the unpaired electron, free radicals tend to seek out other electrons to pair with, which makes them highly reactive chemically. This is because they aim to achieve a stable electronic configuration by either donating, gaining, or sharing an electron.

Step 3: Analyzing the Options

We need to determine which option describes a property associated with free radicals. Option (a) suggests they are 'chemically reactive,' which aligns with their behavior due to the unpaired electron.

Step 4: Ruling Out Other Options

Options (b), (c), and (d) describe other conditions: 'chemically inactive,' 'anions' (negatively charged ions), 'cations' (positively charged ions). These do not accurately describe the nature of free radicals, which are primarily characterized by their reactivity.

Key Concepts

Unpaired Electrons

Free radicals are fascinating entities in the world of chemistry. Atoms or molecules with unpaired electrons in their outermost shell are termed free radicals. This singular electron is quite the anomaly because, under stable conditions, electrons prefer to exist in pairs. The lack of a pairing partner makes this electron highly unstable and, thus, leads to intriguing chemical behaviors.
These unpaired electrons, in their quest for stability, often drive free radicals to participate in chemical reactions. They look to either pair up with another electron, fill or empty their outer shell, or share electrons through covalent bonds. This need to "complete a pair" is the driving force behind their activity in chemical processes. It's like having an incomplete puzzle — eager to find that missing piece to become whole.

• The electron's attempt to find a pair often results in high reactivity.
• This characteristic is the cornerstone of the radical's chemical behavior.

Chemical Reactivity

The term 'reactive' is often used to describe substances or compounds that engage easily in chemical reactions. Free radicals are the epitome of chemical reactivity because their solitary electron is continually in search for another to pair with. This search makes them rather "desperate" for chemical interactions, often without much discrimination.
Interestingly, this high reactivity can be both beneficial and detrimental. For instance, in human biology, reactive oxygen species (a type of free radical) play roles in cell signaling and fighting pathogens. However, excessive free radicals can lead to oxidative stress, which is harmful to cells. Nature carefully balances the production and neutralization of these radicals to harness their reactivity for useful biological functions.

• Free radicals consistently seek stability, which makes them reactive.
• They can either gain, lose, or share electrons to form new compounds.

Stable Electronic Configuration

Every atom, molecule, or ion aspires to reach a state of lowest energy, which is often achieved by having a stable electronic configuration. This means having a full set of electrons in the outermost shell, similar to the noble gases, which are inherently inert due to their complete electron shells. Free radicals disrupt this balance by having an unpaired electron.
To achieve this coveted stability, free radicals will undergo chemical changes. They may form new bonds with other atoms or molecules, "stealing" or "donating" electrons, or aligning with another radical or ion. Their journey to stability usually involves tumultuous chemical adventures, but ultimately, it's all in pursuit of that harmonious state of a filled shell.

• Stability is the driving desire of every atom or molecule.
• Reactivity of radicals stems from the pursuit of a stable electron configuration.