Problem 38 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

$$ \mathrm{SnCl}_{2} \text { is a non-linear molecule. } $$

Step-by-Step Solution

Answer

\(\mathrm{SnCl}_{2}\) is bent due to one lone pair on the Sn atom.

Step 1: Understand the Lewis Structure

First, let's understand the electronic structure of \(\mathrm{SnCl}_{2}\). Tin (Sn) usually has two valence electrons, while each chlorine (Cl) atom has seven valence electrons. \(\mathrm{SnCl}_{2}\) will involve the tin atom forming two single bonds with the chlorine atoms, resulting in a total of four shared electrons.

Step 2: Determine Electron Geometries

Now, consider the number of regions of electron density around the Sn atom. There are two bond pairs and one lone pair of electrons around Sn.

Step 3: Apply VSEPR Theory

According to VSEPR (Valence Shell Electron Pair Repulsion) theory, electron pairs will arrange themselves to minimize repulsion. The typical arrangement for one lone pair and two bond pairs around a central atom is trigonal planar; however, with one lone pair, the shape is bent (or angular).

Step 4: Conclude the Molecular Shape

Considering the VSEPR theory applied above, \(\mathrm{SnCl}_{2}\) has a bent shape due to the presence of a lone pair. This non-linear geometry results in the molecule not being a straight line.

Key Concepts

Lewis Structure

The Lewis Structure is a fundamental concept in chemistry that helps visualize the arrangement of atoms within a molecule. It provides insight into how atoms are connected and the distribution of electrons. For \( \mathrm{SnCl}_2 \), we start by identifying the valence electrons. Tin (Sn) typically contributes two valence electrons, while each chlorine (Cl) atom brings seven valence electrons. The construction of the Lewis Structure involves connecting the tin atom to each chlorine atom with a single bond.

In this case, tin shares its two electrons, forming a stable environment by bonding with the chlorines. This results in:

• Two single Sn--Cl bonds
• A total of four electrons being shared in these bonds

It's important to depict any lone pairs as well. Tin, after forming bonds with the chlorines, will also have a lone pair of electrons, which is crucial when determining the molecular geometry.

Molecular Geometry

Molecular Geometry refers to the three-dimensional arrangement of the atoms within a molecule. This arrangement is a critical aspect that dictates many properties, such as polarity and reactivity. In the case of \( \mathrm{SnCl}_2 \), the geometry is influenced by both the bonded pairs and the lone pair of electrons on the tin.

Applying the Valence Shell Electron Pair Repulsion (VSEPR) theory is essential for understanding molecular shapes. This theory states that electron pairs, both bonding and non-bonding, will spread out as far as possible to minimize repulsion. For \( \mathrm{SnCl}_2 \):

• Two Sn--Cl bonds exist
• One lone pair of electrons resides on the Sn atom

Despite having a potential for trigonal planar geometry, due to the lone pair, the shape turns bent or angular. The lone pair occupies more space and pushes the bonded atoms closer together, resulting in a non-linear molecular structure.

Electron Pairs

Electron Pairs play a significant role in determining the shape and properties of a molecule. They can be categorized as either bonding pairs or lone pairs. In \( \mathrm{SnCl}_2 \):

• The bonding pairs are responsible for holding the atoms together via chemical bonds.
• Lone pairs are pairs of valence electrons that do not participate in bonding but still reside on an atom.

In the structure of \( \mathrm{SnCl}_2 \), the tin atom is connected to two chlorine atoms, forming two bonding electron pairs. Additionally, there is a lone pair on tin. Lone pairs can exert a stronger repulsive force than bonded pairs.

This distinction is crucial for predicting molecular geometry as explained by VSEPR theory. The lone pair around the tin atom in \( \mathrm{SnCl}_2 \) makes the electron geometry trigonal planar, but due to the shape distortion caused by the lone pair, the molecular geometry is ultimately bent.