Problem 58 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is a correct set? (a) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{sp}^{3}\), angular (b) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{sp}^{2}\), linear (c) \(\mathrm{NH}_{4}^{+}, \mathrm{dsp}^{2}\), square planar (d) \(\mathrm{CH}_{4}, \mathrm{dsp}^{2}\), tetrahedral

Step-by-Step Solution

Answer

Correct set: _2O, sp^3, angular] (option a).

Step 1: Analyze Option (a)

Option (a) states _2O, sp^3, angular]. Water ([_2O] has two hydrogen atoms and two lone pairs around the oxygen atom. The geometry of water is bent or angular because of the two lone pairs. The hybridization of the oxygen atom in water is p^3] to accommodate the lone pairs and bonds. So, option (a) is correct.

Step 2: Analyze Option (b)

Option (b) states _2O, sp^2, linear]. Water is not linear; it is angular. Moreover, water has p^3] hybridization, not p^2]. Therefore, this option is incorrect.

Step 3: Analyze Option (c)

Option (c) states H_4^+, dsp^2, square planar]. The ammonium ion (H_4^+]) is tetrahedral in shape, not square planar. Its hybridization is p^3], not sp^2]. Thus, this option is incorrect.

Step 4: Analyze Option (d)

Option (d) states H_4, dsp^2, tetrahedral]. Methane (H_4]) is indeed tetrahedral due to four identical hydrogen atoms surrounding a carbon. However, its hybridization is p^3], not sp^2]. Therefore, this option is incorrect.

Step 5: Conclusion

Based on the hybridization and molecular geometry, option (a) _2O, sp^3, angular] is the only correct set.

Key Concepts

Molecular Geometry

Molecular geometry is all about the 3D arrangement of atoms within a molecule. It significantly impacts the molecule's properties and reactions. Consider water, a classic example. It has two hydrogen atoms and one oxygen, but what's striking is its bent shape. This angular shape is not random. It happens because of the arrangement of electron pairs around the central oxygen atom.

Why is this shape important? Here’s why:

• Polarity: The bent shape of water leads to a polar molecule, giving water its unique properties like high surface tension and boiling point.
• Reactivity: The shape affects how water interacts with other molecules, impacting reactions in chemistry and biology.

The shape of molecules like methane (\(CH_4\)) and ammonium ion \(NH_4^+\) are different. Methane, a tetrahedral molecule, allows even distribution of atoms around the central carbon, making it symmetric and non-polar.

VSEPR Theory

VSEPR theory, short for Valence Shell Electron Pair Repulsion theory, is a foundational concept for predicting molecular geometry. It helps chemists to understand why molecules have the shape they do.

The basic idea is simple:

• Electron Pair Repulsion: Electrons in the valence shell arrange themselves to minimize repulsion. This means bonds and lone pairs spread out as much as possible.
• Determining Shape: The number of electron groups (bonds and lone pairs) around a central atom dictates the geometry. For instance, water has two bonds and two lone pairs, resulting in a bent shape.

This theory explains the tetrahedral shape of methane and why water isn't linear, even though both involve a central atom surrounded by other atoms. Each geometry, like linear, bent, tetrahedral, or square planar, arises to lessen the electron pair repulsion.

Chemical Bonding

Chemical bonding is the force holding atoms together in molecules. It's crucial for explaining how diverse compounds form and behave. There are several types of chemical bonds:

• Covalent Bonds: This involves sharing electron pairs between atoms, as in water (\(H_2O\)) and methane (\(CH_4\)).
• Ionic Bonds: These occur through the transfer of electrons, leading to attraction between positively and negatively charged ions.
• Metallic Bonds: Found in metals where electrons are free to move, giving metals their conductivity.

In water and methane, covalent bonding is key. The geometry of these molecules is directly linked to how these bonds form. The direction and strength of bonds affect a molecule's physical and chemical properties, such as boiling points and reactivity. Understanding these bonds provides insight into molecular stability and interactions.