Is ammonia a tetrahedral molecule?

As a subject matter expert in the field of chemistry, I specialize in understanding the molecular structures and bonding patterns of various compounds. Let's delve into the specifics of ammonia and its molecular geometry. Ammonia, with the chemical formula NH3, is a compound consisting of one nitrogen atom bonded to three hydrogen atoms. To determine the shape of a molecule, we often refer to the Valence Shell Electron Pair Repulsion (VSEPR) theory, which predicts the three-dimensional shape of molecules based on the repulsion between electron pairs in the valence shell of the central atom. For ammonia, the nitrogen atom has five valence electrons. Three of these electrons form sigma (σ) bonds with the three hydrogen atoms, and the remaining two electrons form a lone pair. This gives us a total of four electron pairs around the nitrogen atom in the valence shell. According to VSEPR theory, these electron pairs will arrange themselves to minimize repulsion, which results in a tetrahedral electron pair geometry. However, when considering the molecular geometry, which refers to the arrangement of atoms in a molecule, we only consider the positions of the atoms, not the lone pairs. Since there are three hydrogen atoms bonded to the nitrogen, the molecular geometry of ammonia is trigonal pyramidal, not tetrahedral. The bond angles in a trigonal pyramidal molecule are approximately 107.5 degrees, which is slightly less than the ideal tetrahedral angle of 109.5 degrees. The statement provided regarding the fourth hydrogen bonding to the ammonia molecule as a hydrogen ion (proton) is referring to the formation of an ammonium ion (NH4+). When ammonia reacts with an acid, it can accept a proton to form the ammonium ion. In the case of the ammonium ion, the nitrogen atom is indeed bonded to four hydrogen atoms, and the electron pair geometry is tetrahedral. However, the molecular geometry remains trigonal pyramidal due to the presence of the lone pair, which still exerts a repulsive force on the bonding pairs, pushing them to a trigonal pyramidal arrangement. It's important to note that the presence of hydrogen bonding, such as in solutions of household ammonia or window cleaner, does not change the molecular geometry of the ammonia molecule itself. Hydrogen bonding is an intermolecular force that can influence the properties of a substance, such as its boiling point or solubility, but it does not alter the intramolecular bonding arrangement within individual molecules. In summary, while the electron pair geometry around the nitrogen atom in ammonia is tetrahedral due to the presence of three bonding pairs and one lone pair of electrons, the molecular geometry of ammonia is trigonal pyramidal. The formation of an ammonium ion does result in a tetrahedral molecular geometry, but this is a different species from ammonia.

The fourth hydrogen bonds to the ammonia molecule as a hydrogen ion (no electrons) bonding to the lone pair on the nitrogen. This shows tetrahedral geometry for both the electron pair geometry and the molecular geometry. Ammonium ions are found in solutions of household ammonia or window cleaner.