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

Free radicals are chemically reactive (Option a).

Step 1: Understand What Free Radicals Are

Free radicals are atoms, molecules, or ions that have an unpaired electron in their outer shell. This makes them highly unstable and reactive because they often seek to pair with other electrons to gain stability.

Step 2: Analyze Reactivity Due to Unpaired Electron

The unpaired electron in a free radical is what makes them chemically reactive. This unpaired state causes the free radical to react readily with other chemical species to complete its electron pair, often creating a chain reaction.

Step 3: Evaluate Options

Look at the given options and identify which one correlates with the nature of free radicals. Options include: (a) chemically reactive, (b) chemically inactive, (c) anions, (d) cations. Based on our understanding of free radicals having unpaired electrons and seeking reactions, the best fit is option (a) chemically reactive.

Key Concepts

Unpaired Electrons

Free radicals are unique entities in chemistry, characterized primarily by their unpaired electrons. An electron is stable when it is paired with another in an atomic or molecular orbit. However, in free radicals, one or more of these electrons remain unpaired.
This unpaired state is significant for several reasons. It often results from bond breakage or other chemical processes where a molecule or atom is left with an extra electron lacking a pair. Without a partner to pair with, these unpaired electrons can cause the free radical to search actively for other atoms or molecules to stabilize itself. This search for stability gives free radicals their notable reactivity.
In essence, the unpaired electron is the hallmark of free radicals, making them distinct from stable molecules and compounds, which are typically closed systems with paired electrons.

Chemical Reactivity

The chemical reactivity of free radicals is primarily driven by their unpaired electrons. Unlike stable atoms or molecules that have paired electrons in a balanced arrangement, free radicals are like open-ended puzzles. They have a missing piece, and nature abhors a vacuum.
Because of this unpaired electron, free radicals are highly reactive. They eagerly interact with other molecules to find an electron to pair with. When they succeed, they form new covalent bonds, often resulting in significant chemical changes.

• Free radicals can initiate chain reactions, leading to a cascade of events in biochemical processes.
• They play a crucial role in combustion, polymerization, and even in some metabolic and pathological processes in the body.

Due to their aggressiveness, free radicals are sometimes termed as the 'unruly elements' in chemistry. Their reactivity is both a boon and a bane, leading to important chemical transformations as well as potential damage if uncontrolled.

Stability in Chemistry

In the vast world of chemistry, stability is synonymous with low reactivity. Stable molecules have balanced electron distributions with paired electrons filling their orbital shells.
For free radicals, achieving stability is their ultimate goal. Their unpaired electron results in instability, making them highly reactive in an attempt to achieve a more stable, lower-energy state.
There are several ways a free radical can stabilize:

• Reacting with a neighboring molecule to form a new chemical bond.
• Pairing up its electron with another unpaired electron in a different free radical, thereby neutralizing both species.

This drive for stability is why free radicals are short-lived in most environments. They are like sprinters in a race towards equilibrium, constantly seeking opportunities to stabilize by accepting or donating an electron.
Understanding these concepts is essential for grasping how free radicals influence both chemical and biological processes.