Question

A nitrite ion, \(\mathrm{NO}_{2}^{-},\) can bond to an oxygen atom to form the nitrate ion. Draw the electron dot formula for \(\mathbf{N O}_{3}^{-}\) and label a coordinate covalent bond.

Short answer

NO₃⁻ has a coordinate covalent bond from an oxygen to nitrogen. Total 24 valence electrons.

Step-by-step solution

Determine the total number of valence electrons

For the nitrate ion \( \text{NO}_3^- \): nitrogen (N) has 5 valence electrons, each oxygen (O) has 6 valence electrons, and there is an extra electron due to the negative charge. Sum them up:- Nitrogen: 5 electrons- 3 Oxygens: 3 \times 6 = 18 electrons- Extra electron (from charge): 1 electronTotal = 5 + 18 + 1 = 24 valence electrons.

Draw skeleton structure

Place nitrogen (N) in the center because it is less electronegative than oxygen. Connect each oxygen atom to the nitrogen with a single bond. This utilizes 3 pairs of electrons or 6 electrons total (1 pair per bond).

Distribute remaining electrons

After the bonds in the skeleton structure, divide the remaining electrons to complete the octet around the oxygen atoms first. We've used 6 electrons, leaving us with 18 electrons to distribute. Add 6 electrons (3 pairs) to each of the outer oxygen atoms to complete their octets.

Check the octet and adjust for charge

After giving each oxygen an octet, the nitrogen doesn't have a full octet. One oxygen shares a lone pair to form a coordinate covalent bond, making a double bond with nitrogen. Now check: - N has 8 electrons around it. - Two O's with single bonds each "see" 8 electrons. - One O with a double bond also "sees" 8 electrons.

Label the coordinate covalent bond

The oxygen that donated a pair of electrons to form a double bond with nitrogen is involved in a coordinate covalent bond. Label this bond with an arrow pointing from the oxygen (''\( \overset{..}{O} \to \) N'') towards nitrogen showing the origin of the electrons.

Verify electron count and charge

Ensure that all valence electrons (24 in total) are accounted for in the structure, and the overall charge of the ion is -1 due to the extra lone pair electron that fills out the structure.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how atoms bond with each other. In the case of the nitrate ion \(\mathrm{NO}_3^-\), understanding the number of valence electrons helps us build its structure.
Nitrogen (N) has 5 valence electrons, and each oxygen (O) atom brings 6 valence electrons to the table. When forming the nitrate ion, we account for not only the electrons from the atoms themselves but also an additional electron due to the overall negative charge of the ion.
So, we have:

• 5 electrons from nitrogen,
• 6 electrons for each of the 3 oxygen atoms (totaling 18),
• Plus 1 extra electron from the negative charge.

This brings us to a total of 24 valence electrons that we need to distribute throughout the nitrate structure to satisfy octet rules.

Coordinate Covalent Bond

A coordinate covalent bond, also known as a dative bond, occurs when one atom donates a pair of electrons to another atom that lacks a complete set. In the nitrate ion \(\mathrm{NO}_3^-\), the nitrogen center atom does not have a complete octet once each oxygen is given its usual share.
To resolve this electron deficit, one oxygen atom shares its lone pair of electrons with nitrogen, forming a double bond. When this happens, both electrons in the bond originate from only one atom—the oxygen—showing the nature of a coordinate covalent bond.
This bond is usually represented by an arrow (") pointing from the donor atom (oxygen) to the acceptor atom (nitrogen), signaling the direction of electron donation. It's an important concept because while it forms the same kind of covalent bond seen in typical shared pairs, it indicates that one atom initially provided all the electrons involved in the bond.

Electron Dot Formula

An electron dot formula, also known as a Lewis structure, is a handy visualization tool showing the arrangement of electrons around atoms within a molecule. For the nitrate ion (\(\mathrm{NO}_3^-\)), this involves placing nitrogen (N) in the center with oxygen atoms forming bonds around it.
We start by sketching the skeleton structure with nitrogen at the center bonded to three oxygen atoms. Given we determined there are 24 valence electrons, we use 6 electrons to form single bonds between N and each O (2 electrons per bond).
After this setup, we distribute the remaining electrons to accomplish octet configurations for all atoms. Ensuring the outer oxygen atoms complete their octet first, we subsequently address the central nitrogen's need.

• Assign 6 electrons (3 pairs) to each oxygen atom to complete their octet.
• Note that nitrogen might still lack electrons to complete its octet.
• Form a double bond using one of the lone pairs from an oxygen atom to create a coordinate covalent bond.

The final electron dot formula not only helps us neatly visualize the molecule but also allows verification of the total count of valence electrons and the molecular charge.