Question

Consider the nitryl cation, \(\mathrm{NO}_{2}^{+} .\) (a) Write one or more appropriate Lewis structures for this ion. (b) Are resonance structures needed to describe the structure? (c) With what familiar molecule is it isoelectronic?

Short answer

(a) The Lewis structures for the nitryl cation (NO2+) are O=N-O and O-N=O. (b) Resonance structures are needed to describe the structure of the nitryl cation, as a single Lewis structure cannot represent all possible electron configurations for this ion. (c) The nitryl cation (NO2+) is isoelectronic with the carbon dioxide molecule (CO2), as both have a total of 16 valence electrons.

Step-by-step solution

Find Total Number of Valence Electrons

To construct the Lewis Structure of NO2+ ion, we need to calculate the total number of valence electrons. Nitrogen has 5 valence electrons, and each Oxygen atom has 6 valence electrons. Since the ion has a +1 charge, we will subtract 1 electron. 5 (from Nitrogen) + 6 * 2 (from two Oxygen atoms) - 1 (for +1 charge) = 16 valence electrons

Draw the Lewis Structure

Next, we will arrange the atoms and use the 16 valence electrons to form bonds and distribute the remaining electrons as lone pairs. Place Nitrogen as the central atom and connect it to the two Oxygen atoms using single bonds. Now we have used 4 electrons for bonding. Remaining valence electrons: 16 - 4 = 12 Place 3 lone pairs (6 electrons) on one Oxygen atom, and 2 lone pairs (4 electrons) on the other Oxygen atom. Then, use the remaining 2 electrons to form a double bond between Nitrogen and one of the Oxygen atoms. O=N-O The resulting Lewis structure should have 3 single bonds and 1 double bond, satisfying the octet rule for Nitrogen and both Oxygen atoms.

Determine Whether Resonance Structures Are Needed

Resonance structures are required when a single Lewis structure cannot represent all possible electron configurations or when a single structure does not completely describe the actual molecule. In this case, the Lewis structure we drew with a double bond to one Oxygen and a single bond to the other Oxygen can also have the double bond to the other Oxygen atom. O-N=O So, resonance structures are indeed needed to describe the structure of the nitryl cation.

Identify the Isoelectronic Familiar Molecule

Isoelectronic species have the same total number of valence electrons and the same electron configuration. In our nitryl cation, we have 16 valence electrons. CO2 (carbon dioxide) has 4 valence electrons from Carbon and 2 * 6 valence electrons from the two Oxygen atoms, making a total of 16 valence electrons, just like our nitryl cation. Therefore, the nitryl cation (NO2+) is isoelectronic with the carbon dioxide molecule (CO2).

Key concepts

Valence Electrons

Valence electrons are the electrons situated in the outermost shell of an atom. These electrons are crucial because they are the ones participating in chemical bonding. When forming a Lewis structure, like that of the nitryl cation (O_2^+), it's essential to calculate the total number of valence electrons to determine how atoms will bond and whether they'll share electrons to form stable molecules or ions.

For the nitryl cation, we start by adding the valence electrons of nitrogen (which has 5) to those of oxygen (each has 6, so that's 12 for two oxygens), giving us 17 electrons. However, because we are dealing with a positively charged ion, we subtract one electron, arriving at 16 valence electrons that we can distribute in the Lewis structure.

Understanding valence electrons is key in predicting molecular geometries, bond strengths, and the physical and chemical properties of molecules. They are the building blocks of structures and enable us to grasp the principles behind molecular stability and reactivity.

Resonance Structures

Resonance structures are a set of two or more Lewis structures that collectively describe the real, intermediate bonding nature of a molecule where bond distribution can't be represented by a single, definitive Lewis Structure. With nitrogen dioxide cation (O_2^+), resonance structures are indeed necessary.

After drawing the initial Lewis structure, we notice that the arrangement of electrons allows both oxygen atoms to potentially share a double bond with nitrogen. Because a single Lewis structure can't represent this variability, we draw resonance structures by shifting a pair of bonding electrons between nitrogen and each oxygen atom. These alternative structures underscore the notion that electrons are delocalized – they're not fixed in place, but rather, have several possible positions they could occupy.

The benefit of using resonance is that it gives a more accurate depiction of where electrons might be found in a molecule, thus painting a more realistic picture of molecular structure. Resonance structures do not exist independently of each other, but rather, the true structure is a hybrid of the resonant forms.

Isoelectronic Species

Isoelectronic species are atoms, ions, or molecules that have the same number of valence electrons and therefore a similar electronic configuration. This results in similar chemical and physical properties among isoelectronic species, despite possibly having different elements.

In our example, the nitryl cation (O_2^+) and carbon dioxide (CO2) are isoelectronic. Both have a total of 16 valence electrons. This resemblance can guide predictions about the molecular shape and bond angles of the cation because isoelectronic species often share molecular geometries.

Being isoelectronic to carbon dioxide means that the O_2^+ ion has a linear structure, just like CO2. This concept is an excellent illustration of how understanding one molecule can extend insights to another, showcasing the elegance and patterns within chemical structures. Isoelectronic species can be foundational in understanding various aspects of chemical reactions and material behaviors.