Question

These species have been detected in interstellar space: (a) \(\mathrm{CH},\) (b) \(\mathrm{OH},\) (c) \(\mathrm{C}_{2},\) (d) \(\mathrm{HNC}\), (e) HCO. Draw Lewis structures of these species and indicate whether they are diamagnetic or paramagnetic.

Short answer

The Lewis Structures are: CH has a single bond between Carbon and Hydrogen, OH has a single bond between Oxygen and Hydrogen, C2 has a triple bond between the two Carbon atoms, HNC has a single bond between Hydrogen and Nitrogen and a triple bond between Nitrogen and Carbon, HCO has a single bond between Hydrogen and Carbon and a double bond between Carbon and Oxygen. CH and C2 are paramagnetic, OH, HNC and HCO are diamagnetic.

Step-by-step solution

Draw Lewis Structures

The Lewis structures of the molecules are drawn as follows: \(a) \mathrm{CH}\) ({Carbon with 3 lone pair electrons and a Single bond with Hydrogen which has one lone pair), \(b) \mathrm{OH}\) (oxygen atom linked to hydrogen atom by a single bond with 6 electrons in the outer shell of oxygen), \(c) \mathrm{C}_{2}\) (Both Carbon atoms are linked by triple bond with each carbon having two lone electrons.), \(d) \mathrm{HNC}\) (Nitrogen linked to Hydrogen by a single bond and to Carbon by a triple bond, Nitrogen has a lone pair of electrons.), \(e) \mathrm{HCO}\) (Carbon atom at the center, linked to Hydrogen by a single bond and to Oxygen by a double bond, there are three lone pairs on Oxygen).

Determine Magnetic properties

Now, looking at the structures, observing their electron configurations: \(a) \mathrm{CH}\) has unpaired electrons (in carbon), indicating it is paramagnetic, \(b) \mathrm{OH}\) has all paired electrons, thus it is diamagnetic, \(c) \mathrm{C}_{2}\) has unpaired electrons (in each carbon), indicating it is paramagnetic, \(d) \mathrm{HNC}\) has all paired electrons, thus it is diamagnetic, \(e) \mathrm{HCO}\) has all paired electrons, thus it is diamagnetic.

Key concepts

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. These structures are pivotal in understanding the arrangement of electrons around an atom which, in turn, can predict the chemical properties and behavior of a substance.

To draw a Lewis structure, one must know the total number of valence electrons in the molecule. Then, these electrons are arranged to fill the outer shells of each atom, often resulting in pairs. Atoms will share electrons to fulfill the octet rule, or having eight electrons in their valence shell, which is a key principle in chemistry for most main group elements. Hydrogen, being an exception, follows the duet rule, where it seeks to have two electrons in its valence shell.

The Lewis structures in this exercise, for the listed interstellar species, serve as a basis to determine the magnetic properties of these molecules which is key to understanding their behavior in the presence of an external magnetic field.

Paramagnetic Substances

Paramagnetic substances are materials that have at least one unpaired electron in their electron configuration. This unpaired electron creates a magnetic moment, which can interact with magnetic fields. As a result, paramagnetic substances are attracted by external magnetic fields.

When a paramagnetic substance is placed in a magnetic field, the unpaired electrons align with the field, and the substance shows a net attraction. The presence of unpaired electrons can be determined using Lewis structures, where unpaired dots represent the unpaired electrons. The substance CH from the exercise, with its unpaired electron, is an example of a paramagnetic substance, as is C2 because each carbon has an unpaired electron.

Diamagnetic Substances

Diamagnetic substances, on the other hand, are those that do not contain any unpaired electrons. All the electrons in these materials are paired up and, hence, do not create a magnetic moment. This causes diamagnetic substances to slightly repel magnetic fields.

In the presence of a magnetic field, the electron orbits shift slightly due to an induced magnetic field which opposes the external field. However, since the electrons are all paired, the overall effect is weak and doesn't result in an attraction to the magnetic field. Examples from the exercise include OH, HNC, and HCO, all of which have all of their electrons paired as shown in their Lewis structures.

Molecular Electron Configuration

The molecular electron configuration describes the distribution of electrons in a molecule which is not only important to understand Lewis structures but also the magnetic properties. It gives a visual depiction of both the bonding and non-bonding electrons, illustrating how electrons are shared between atoms or exist as lone pairs.

Knowledge of molecular electron configurations helps predict molecular geometry, potential reaction mechanisms, and physical properties such as magnetism. As we saw in the species from the exercise, knowing whether electrons are paired or unpaired within molecular orbitals can tell us if the molecule will be paramagnetic or diamagnetic, which has practical implications in fields like spectroscopy and material science.

Grasping the concepts of Lewis structures and molecular electron configuration is essential for students to accurately predict the magnetic behavior of substances and understand their chemical properties.