Problem 92 - A Complete Resource Book in Chemistry for JEE Main

Question

In \(\mathrm{X}-\mathrm{H}-\mathrm{Y}\), where both \(\mathrm{X}\) and \(\mathrm{Y}\) are electronegative elements (a) electron density of \(\mathrm{X}\) will increase and the electron density on \(\mathrm{H}\) will decrease (b) on both species electron density will increase (c) on both species electron density will decrease (d) on \(\mathrm{X}\) the electron density will decrease and on \(\mathrm{H}\) it will increases

Step-by-Step Solution

Answer

(a) Electron density on X will increase; on H will decrease.

Step 1: Understanding electronegativity

Electronegativity is the tendency of an atom to attract electrons towards itself. In a bond between two different atoms, the more electronegative atom will attract more electron density.

Step 2: Analyzing the X-H-Y bond structure

In the given structure, X and Y are electronegative elements bonded to H. The electron density will tend to move towards the more electronegative elements (X and Y) from H, as electronegative atoms attract electrons.

Step 3: Electron distribution in X-H-Y

Due to the electronegativity of X and Y, electrons are pulled closer to these atoms. This means the electron density on X and Y will increase, while the electron density on H will decrease since electrons are being drawn away from it.

Step 4: Evaluating the options

Based on the analysis, the correct description is that the electron density on X will increase and the electron density on H will decrease. This matches with option (a).

Key Concepts

Electron Density

Electronegativity plays a crucial role in determining electron density within a molecule. At its core, electron density refers to the probability of finding an electron in a particular space around an atom. In chemical bonding, electron density is not spread uniformly. Instead, it gets redistributed based on the electronegativity of the atoms involved.

When atoms such as X and Y, which are both electronegative, exist in a bond with hydrogen (H), they attract electron density towards themselves. This phenomenon causes electron density to shift. Thus, in the X-H-Y bond scenario, the electron density will increase around X and Y because these atoms are pulling the electrons closer. On the other hand, the electron density around H will decrease as it loses its electrons to the more electronegative X and Y.

Bond Structure

The structure of a bond dictates how electrons are distributed between the atoms involved. A basic understanding is crucial to predict the outcome of electron density distribution. In the X-H-Y molecular structure, X and Y are bonded to H, and all atoms have varying degrees of electronegativity.

This particular bond structure highlights the concept that electrons are not static but rather move towards regions with higher electronegativity. The X-H-Y bond structure demonstrates that X and Y, being electronegative, create a scenario where electron sharing is unequal. This unequal sharing leads to an uneven distribution of electron density. Such structures are quite common in chemistry, especially in organic chemistry, where polar bonds often arise due to differences in electronegativity among atoms making up a molecule.

Attract Electrons

Electronegative atoms have a strong tendency to attract electrons. This happens because these atoms have a greater number of protons, creating a positive charge that can attract negative electrons more effectively.

• In the X-H-Y bond formation, both X and Y are drawn to electrons because of their high electronegativity. They exert a force on the shared electrons with H, pulling them closer.
• This attracting force results in an increase in electron density around these atoms and a decrease in the electron density around hydrogen.
• The difference in the attraction strength of electrons between atoms sets the stage for polar covalent bonds, where one atom gains a slight negative charge while the other becomes slightly positive.

This attraction is a fundamental property of atoms and is crucial for understanding how molecules behave and react.