Using the VSEPR theory, predict the molecular structure of each of the following polyatomic ions

Using the VSEPR theory, predict the molecular structure of...

Key Concepts

Molecular Geometry

Molecular geometry describes the actual three-dimensional layout of atoms in a molecule, which is derived from the electron domain geometry after accounting for the positions of the atoms only (excluding lone pairs). The presence of lone pairs can modify the idealized angles and cause deviations from perfect geometries, leading to shapes such as bent, seesaw, or trigonal pyramidal.

Lone Pair Repulsion

Lone pair repulsion is a key concept in VSEPR theory, emphasizing that non-bonding electron pairs exert a stronger repulsive force than bonding pairs. This increased repulsion affects bond angles and can lead to distortions in the molecular geometry compared to the idealized shapes predicted solely by considering bonding pairs.

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) theory is a model used to predict the three-dimensional arrangement of atoms in a molecule by considering the repulsive interactions between electron pairs in the valence shell of the central atom. The basic premise is that electron pairs, both in bonds and as lone pairs, will spread out as much as possible around the central atom to minimize repulsions, thereby determining the molecule's geometry.

Electron Domain Geometry

Electron domain geometry refers to the overall spatial arrangement of all electron groups (bonding pairs and lone pairs) around a central atom. By counting these groups, one can determine an idealized geometry—such as linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral—that forms the basis from which the actual molecular shape is derived.

Transcript

00:01 In this question, we are determining the structure of polyatomic ions by using vesper theory.

00:07 First, we are looking at the dihydrogen phosphate ion, and our first step is to be counting the number of available valence electrons.

00:16 So we have two hydrogens, each which have one valence electron, a phosphate with five valence electrons, four oxygens with six valence electrons each, and an overall charge of negative one indicates that we have one.

00:30 Extra electron because each electron has a charge of negative 1.

00:34 We add this together and we get 32.

00:37 Phosphate is our central atom.

00:39 We have four oxygens branching off.

00:43 We then attach our two hydrogens to our oxygens.

00:49 Now we count the number of electrons that have already been implemented.

00:54 So each of our bonds here has two electrons.

00:57 We have one, two, three, four, five, six bonds.

01:03 So that's 12 electrons, meaning we have 20 more to distribute.

01:08 So we start with our oxygens, 6, 12, 16, 20.

01:18 Our hydrogens won't get any electrons because they only have room for two valence electrons in their shells and their first valence shells and those have already been fulfilled with the bond.

01:29 Now we have four bonding pairs around our central atom of phosphate, and according to vesper, that is a tetrahedral.

01:43 Next, we are looking at the perchlorate ion.

01:45 Here we have seven valence electrons from chlorine, six valence electrons from our four oxygens, and an added charge of an added electron for the negative one charge.

01:57 This gets us to 32...

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