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OAE Chemistry Sample Test

1 of 5

The molecule NH₃ is an example of which type of molecular geometrical structure?

Correct Answer:

trigonal pyramidal.
the correct geometrical structure of the nh3 (ammonia) molecule is trigonal pyramidal.

the structure of a molecule is determined based on the arrangement of the electron pairs around the central atom. in nh3, the central atom is nitrogen (n), which has five valence electrons. three of these electrons form bonds with three hydrogen atoms, and the remaining two electrons form a lone pair. the presence of this lone pair and the three bonding pairs of electrons influences the molecular geometry, making it different from a perfect tetrahedral shape.

in a perfect tetrahedral geometry, the bond angles between the atoms are about 109.5 degrees. however, in nh3, the lone pair exerts a greater repulsive force on the bonding electron pairs than the bonding pairs exert on each other. this repulsion between the lone pair and the bonding pairs slightly distorts the geometry, reducing the bond angles to slightly less than 109.5 degrees.

this distortion due to the lone pair results in a trigonal pyramidal geometry. in a trigonal pyramidal shape, three atoms are positioned at the corners of a pyramid with a triangular base, and the central atom is above the base at the apex of the pyramid. the lone pair occupies the space above the nitrogen, pushing the three hydrogen atoms downwards.

this explanation underscores why nh3 cannot be described as octahedral, t-shaped, or trigonal planar: - octahedral would require six atoms or groups of electrons around the central atom arranged at 90 degrees to each other. - t-shaped is typically observed in molecules with three bonding pairs and two lone pairs in a different arrangement. - trigonal planar involves three atoms bonded to the central atom in a flat plane with 120-degree bond angles, with no lone pairs affecting the geometry. thus, the unique arrangement of electron pairs in nh3 definitively classifies it as having a trigonal pyramidal molecular geometry.