Problem 84 - Introductory Chemistry Atoms First

Question

Hydrogen peroxonitrite has the formula HNO_{s} with the atoms connected \(\mathrm{O}-\mathrm{N}-\mathrm{O}-\mathrm{O}-\mathrm{H}\). (a) Draw the dot diagram for this molecule. (b) Draw the three-dimensional shape of the molecule, showing the numeric value of all bond angles. (c) Describe the electron-group geometry and molecular shape around the \(\mathrm{N}\) and around each \(\mathrm{O}\) to the right of the \(\mathrm{N}\).

Step-by-Step Solution

Answer

The Lewis structure for hydrogen peroxonitrite is shown below: \(O= N (O-)-(O^- H) \) The three-dimensional shape of the molecule is as follows: - The N atom has trigonal planar electron-group geometry with bond angles of 120°. Its molecular shape is also trigonal planar. - The first O to the right of N has bent molecular shape and an electron-group geometry of trigonal planar with a bond angle of 120°. - The second O has linear molecular shape and an electron-group geometry of linear with a bond angle of 180°. In conclusion, hydrogen peroxonitrite has linear and bent molecular geometries, with bond angles of 120° and 180°.

Step 1: Drawing the Lewis structure

First, let's draw the Lewis structure for hydrogen peroxonitrite. Remember that the formula is HNO_{s} and the atoms are connected in the order O-N-O-O-H. In order to draw the Lewis structure, we need to follow these steps: 1. Count the total number of valence electrons in the molecule: - Oxygen has 6 valence electrons, and there are 3 oxygen atoms, so we have 3 x 6 = 18 electrons from oxygen. - Nitrogen has 5 valence electrons. - Hydrogen has 1 valence electron. - Adding these up, we get 18 + 5 + 1 = 24 valence electrons. 2. Arrange the atoms in the given order and connect them with single bonds. 3. Fill the octet for the external atoms (O and H) using remaining valence electrons. It's okay to have more than 8 electrons around central N. 4. Add any leftover valence electrons to the central atom (N). Following these steps should give you the correct Lewis structure.

Step 2: Draw the three-dimensional shape

Now, let's draw the three-dimensional shape of the molecule and determine the bond angles: 1. Determine the electron group geometry for each atom, which can be found using VSEPR (valence shell electron pair repulsion) theory. Keep in mind that we need to consider both the lone pairs of electrons and the bonded pairs around each atom. 2. Describe the molecular shape, excluding the lone pairs, for each atom. 3. Determine the numeric value of bond angles.

Step 3: Describe the electron-group geometry and molecular shape

Finally, we will describe the electron-group geometry and molecular shape around the nitrogen (N) and each oxygen (O) to the right of the nitrogen: 1. Considering the arrangement of the atoms and the electrons around each atom from the Lewis structure, determine the electron-group geometry for each specified atom. 2. Determine the molecular shape (excluding lone pairs) around each atom. When you've completed all these steps, you should have the following information: a) Lewis structure for hydrogen peroxonitrite b) Three-dimensional shape of the molecule, with numeric bond angles c) Electron-group geometry and molecular shape for nitrogen and each oxygen to the right of nitrogen.

Key Concepts

Lewis Dot Structure

The Lewis dot structure is a representation of a molecule that shows how atoms are bonded together, and the locations of any unbonded electron pairs. To create a Lewis dot structure for a molecule like hydrogen peroxonitrite (HNO_s), you count the total number of valence electrons for all atoms involved. With 24 valence electrons to work with, you then arrange the atoms as specified (O-N-O-O-H) and connect them with single bonds. After that, complete the octets for the outer atoms and distribute any remaining electrons to the central atom, in this case, nitrogen. The Lewis structure provides a foundation for understanding the molecule's shape and bonding.

For hydrogen peroxonitrite, the Lewis structure can help students see that oxygen and nitrogen atoms form a chain with a hydrogen atom at one end. This structure is crucial for predicting the molecule's geometry and behaviour.

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual atoms in molecules. It states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion between them. This theory is used after generating the Lewis dot structure and is foundational for sketching the molecular geometry. Since electron groups include both bond pairs and lone pairs, VSEPR theory helps predict the correct molecular shape based on the number and type of these electron groups.

In the exercise for hydrogen peroxonitrite, VSEPR theory guides us to establish the electron-group geometry for each atom and then derive the molecular shape. This theory assists students in transforming a flat Lewis structure into a three-dimensional shape by considering all electron pairs.

Molecular Geometry

Molecular geometry refers to how atoms in a molecule are arranged in three-dimensional space. This arrangement significantly influences the molecule's physical and chemical properties. By applying VSEPR theory to the Lewis dot structure of hydrogen peroxonitrite, one can predict the three-dimensional arrangement of atoms. The geometry around each atom is defined by the electron domains—regions where electrons are likely to be found, such as in bonds or lone pairs.

Identifying the molecular geometry involves looking at each atom's electron domains and predicting shapes like linear, trigonal planar, tetrahedral, or others. In hydrogen peroxonitrite's case, each oxygen and the nitrogen will have specific geometries dictated by how many electron domains surround them. This concept is crucial for understanding not just the visual aesthetic of molecules but also their reactivity and interactions with other molecules.

Bond Angles

Bond angles are the angles between adjacent bonds on a molecule and are determined by the molecule's geometry. They are critically important for understanding the spatial arrangement of a molecule. Derived from the molecular geometry, which VSEPR theory predicts, bond angles allow chemists to visualize how atoms are positioned relative to one another in three dimensions. Measuring these angles helps show the true shape of the molecule, as two molecules with the same molecular formulas can have dramatically different shapes due to variations in bond angles.

In our exercise with hydrogen peroxonitrite, once we have used the VSEPR theory to determine the geometries around the nitrogen and oxygen atoms, we can deduce the bond angles. These angles help illustrate the molecule's shape more accurately, allowing students to visualize how hydrogen peroxonitrite might interact with other molecules, which affects its chemical properties and potential reactions.