QQuestionAdvanced Placement
QuestionAdvanced Placement
Discuss the difference between tetrahedral, pyramidal, and trigonal planar molecular geometries.
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Step 1**Tetrahedral Molecular Geometry**
In tetrahedral molecular geometry, there are four bonds or electron pairs around the central atom, forming a shape that resembles a tetrahedron (a pyramid with a triangular base). The bond angles are approximately 109.5 degrees. This geometry is common in compounds where the central atom has four single bonds, such as methane (CH4). For example, consider a molecule of methane (CH4). The carbon atom is in the center, bonded to four hydrogen atoms. If you were to draw lines connecting each hydrogen atom, you would form a tetrahedron.
Step 2**Pyramidal Molecular Geometry**
Pyramidal molecular geometry is similar to tetrahedral, but with one lone pair of electrons on the central atom instead of a bond. This geometry typically occurs when the central atom has three bonds and one lone pair, such as in ammonia (NH3). For instance, in an ammonia molecule (NH3), the nitrogen atom is in the center, bonded to three hydrogen atoms and has one lone pair of electrons. The bond angle is reduced from the ideal tetrahedral angle due to the repulsion between the lone pair and the bonding pairs, resulting in approximately 107 degrees.
Final Answer
Trigonal planar molecular geometry features a central atom with three bonds or electron pairs in a flat, trigonal arrangement. Each angle between the bonds is 120 degrees. This geometry is common in compounds where the central atom has three single bonds, like boron trifluoride (BF3). Take, for example, boron trifluoride (BF3). The boron atom is in the center, bonded to three fluorine atoms. If you were to draw lines connecting each fluorine atom, you would form an equilateral triangle, indicating the trigonal planar geometry. In summary, the main differences between these geometries are the number of bonds/electron pairs and the bond angles. Tetrahedral geometry has four bonds/electron pairs with approximately 109.5 -degree angles, pyramidal geometry has three bonds and one lone pair with approximately 107 -degree angles, and trigonal planar geometry has three bonds with 120 -degree angles.
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