Question

Which of the following is correct pair? (a) \(\mathrm{NH}_{3}\), linear (b) \(\mathrm{BF}_{3}\), octahedral (c) \(\mathrm{BeCl}_{2}\), liner (d) \(\mathrm{CO}_{2}\), tetrahedral

Short answer

The correct pair is (c) \(\mathrm{BeCl}_{2}\), linear.

Step-by-step solution

Identify the Molecular Geometry of Each Option

We need to determine the molecular geometry of each compound. \(\mathrm{NH}_{3}\) (ammonia) has a trigonal pyramidal shape. \(\mathrm{BF}_{3}\) (boron trifluoride) is trigonal planar. \(\mathrm{BeCl}_{2}\) (beryllium chloride) is linear. \(\mathrm{CO}_{2}\) (carbon dioxide) is also linear.

Examine the Options for Correctness

Compare each molecular geometry to the descriptions: (a) \(\mathrm{NH}_{3}\) is incorrectly labeled as linear (it is trigonal pyramidal). (b) \(\mathrm{BF}_{3}\) is incorrectly labeled as octahedral (it is trigonal planar). (c) \(\mathrm{BeCl}_{2}\), which is described as linear, is correct. (d) \(\mathrm{CO}_{2}\) described as tetrahedral is incorrect (it is linear).

Select the Correct Pair

The only pair with a correct descriptor is (c) \(\mathrm{BeCl}_{2}\), which is linear. Therefore, \(\mathrm{BeCl}_{2}\) - linear is the correct pair.

Key concepts

VSEPR Theory

VSEPR Theory stands for Valence Shell Electron Pair Repulsion Theory. It helps explain the shape of molecules. At its core, the theory suggests that electron pairs around a central atom will arrange themselves to be as far apart as possible. This minimizes repulsion and stabilizes the molecule's structure.
For example, in a molecule like \(\mathrm{BeCl}_{2}\), there are only two bonding pairs and no lone pairs around the beryllium atom. According to VSEPR Theory, these pairs will orient themselves 180 degrees apart, resulting in a linear shape.

• Lone pairs tend to take up more space than bonding pairs, so they influence molecular shape more strongly.
• This theory can predict geometries but doesn’t handle the absolute positions of atoms.

Overall, VSEPR Theory is essential for understanding why molecules have their specific shapes, which can affect how they interact chemically.

Chemical Bonding

Chemical bonding is the process that holds atoms together in molecules. It involves interactions between the valence electrons of atoms.
There are different types of bonds based on the nature of electron interaction:

• Ionic Bonds: Electrons are transferred from one atom to another, typically between metals and non-metals, forming charged ions.
• Covalent Bonds: Electrons are shared between atoms. This type is common in organic compounds, like \(\mathrm{NH}_{3}\) where nitrogen shares electrons with hydrogen atoms.
• Metallic Bonds: Electrons are shared in a 'sea' among many atoms, typical in metals.

For instance, \(\mathrm{BF}_{3}\) features covalent bonding between boron and fluorine atoms, resulting in a stable trigonal planar shape.

Geometry Determination

Molecular geometry determination is vital in predicting and understanding the properties of compounds. It involves analyzing the arrangement of atoms around a central atom in a molecule.
This process generally includes:

• Counting bonding pairs and lone pairs on the central atom.
• Applying VSEPR Theory to predict the molecule's shape.
• Verifying with experimental data when possible.

In \(\mathrm{CO}_{2}\), carbon forms a double bond with each oxygen, with no lone pairs on the central carbon atom. This results in a linear molecular geometry.
Understanding geometry aids in predicting physical properties like boiling points and solubility, and chemical behaviors like reactivity and polarity. It’s a foundational aspect of chemistry that connects structure with function.