In: Chemistry
Among the four statements given, the second and the third are right. Below is an explanation about why the statements are right or wrong.
•Molecular geometry and electron geometry are always the same for any given molecule.
Answer : False. Only in the absence of lone pair electrons on central atom, the molecular geometry and electron geometry are the same. For example, consider ammonia. The total number of electrons in the outer shell is 8 (5 from nitrogen, 3 from 3 hydrogens). Hence there are 4 pairs of electron and the electron geometry is tetrahedral. Since one of the pair is a lone pair on the nitrogen atom, the shape of the molecule changes to pyramidal. Hence, molecular geometry is not always the same as electron geometry.
•The molecular geometry describes the geometric arrangement of the actual atoms in a molecule.
Answer : True. Molecular geometry determined by the VSEPR theory gives the geometric arrangement in a molecule considering the presence of lone pair and bond pair electrons and the interaction between them.
•There are more possible molecular geometries than there are electron geometries.
Answer : True. For example, in a tetrahedral electronic arrangement, the molecular geometry can be tetrahedral (in the absence of lone pair on central atom), pyramidal (presence of 1 lone pair on central atom) or linear (presence of two lone pairs on central atom). Therefore there are more possible molecular geometries than electron geometries.
•The molecular geometry can be determined without looking at the lone pairs on the central atom.
Answer : False. Lone pairs on central atom play an important role in deciding the geometry. They have to be considered. In the absence of lone pair, both the molecular and electronic geometry will be the same.