What is the expected bond angle in a molecule with a tetrahedral geometry, such as CH4?

• A. 90°
• B. 109.5°
• C. 120°
• D. 104.5°

Answer: (B)

Verified step by step guidance

1. Identify the molecular geometry of the molecule. For CH4, the central carbon atom is bonded to four hydrogen atoms with no lone pairs, which corresponds to a tetrahedral geometry.
2. Recall that the tetrahedral geometry arises from the repulsion between four electron pairs arranged as far apart as possible around the central atom, according to VSEPR (Valence Shell Electron Pair Repulsion) theory.
3. Understand that the ideal bond angle in a perfect tetrahedral arrangement is the angle between any two bonds pointing from the central atom to the corners of a tetrahedron.
4. Use the known ideal bond angle for a tetrahedral molecule, which is approximately \$109.5^{\circ}$, as this angle minimizes electron pair repulsions in three-dimensional space.
5. Compare this ideal bond angle to other common molecular geometries: 90° for octahedral, 120° for trigonal planar, and 104.5° for bent (like in water), confirming that \$109.5^{\circ}$ is the correct expected bond angle for tetrahedral molecules like CH4.