Problem 16 - Chemistry: The Central Science

Question

Describe the bond angles to be found in each of the following molecular structures: (a) trigonal planar, (b) tetrahedral, (c) octahedral, (d) linear.

Step-by-Step Solution

Answer

(a) In a trigonal planar structure, the bond angle is \(120\,degrees\) as three electron pairs are evenly distributed in a plane. (b) A tetrahedral structure has a bond angle of approximately \(109.5\,degrees\). (c) For an octahedral structure, the bond angle is \(90\,degrees\). (d) In a linear structure, the bond angle is \(180\,degrees\).

Step 1: (a) Trigonal Planar Bond Angle

In a trigonal planar molecular structure, there are three electron pairs around the central atom. These electron pairs are spread out evenly in a plane. The bond angle for a trigonal planar structure is 120 degrees, as there are 360 degrees in a circle and the three electron pairs are evenly distributed around the central atom. So, the bond angle is \(360\,degrees \div 3 = 120\,degrees\).

Step 2: (b) Tetrahedral Bond Angle

In a tetrahedral molecular structure, four electron pairs are arranged around the central atom. The bond angle for a tetrahedral structure can be calculated using the inverse cosine function: \(\cos^{-1}(\frac{-1}{3}) \approx 109.5\, degrees\). Hence, the bond angle for a tetrahedral structure is approximately 109.5 degrees.

Step 3: (c) Octahedral Bond Angle

In an octahedral molecular structure, there are six electron pairs arranged around the central atom. In this structure, the electron pairs are located at the vertices of an octahedron and are arranged such that there are two sets of three collinear electron pairs. The bond angle for an octahedral structure is 90 degrees since the electron pairs are positioned perpendicular to each other.

Step 4: (d) Linear Bond Angle

In a linear molecular structure, the central atom is surrounded by two electron pairs. The bond angle in a linear structure is 180 degrees, as both electron pairs are directly opposite each other around the central atom along a straight line.