Introduction

Nitrogen is one of the most common elements on Earth, and it is one of many nonmetals. It has an atomic number of seven, meaning a nitrogen atom has seven protons (and seven electrons). Nitrogen is a gas at room temperature. In certain scenarios, it can be very dangerous, but it has some fascinating chemical properties we will explore in this article. The article is a good review of many broader topics in chemistry, but here they are applied to chemicals with nitrogen. We will not go into much depth of how those concepts work, but will focus on what they help us to understand about nitrogen.

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Valence Shell Electrons

The outer orbital of a nitrogen atom, the \(p^2\) orbital, can carry up to six electrons, just like all other \(p\) orbitals. However, a nitrogen atom will only have three of these slots filled. When reacting with other chemicals, it will often try to take electrons from other atoms/ions to get a full octet. Therefore, the \(N^{3-}\) ion (called the nitride ion) is the most common ion formed from a single nitrogen atom.

However, depending on the surroundings, the nitrogen atom may interact with another atom that is less stable without three or even five additional electrons that nitrogen has. So, although it is much rarer than a nitrogen atom gaining three electrons and becoming \(N^{3-}\), it can also lose three or five electrons to form one of two cations: \(N^{3+}\) or \(N^{5+}\). Chances are, if you are a student, your teacher will only expect you to know that the \(N^{3-}\) ion exists, but trying to explain why the other two nitrogen ions can form is a good review of how orbitals work.

Example 1:If \(Ca_xN_y\) is an ionic compound, what are the most likely values of \(x\) and \(y\)?

Solution:Calcium does not generally form any ions besides \(+2\) cations. Since this is an ionic compound, the nitrogen must be the \(-3\) ion to give the compound a neutral charge. It takes three calcium cations to balance the charge of two nitride anions, so the chemical formula is \(Ca_3N_2\). In this compound, called calcium nitride, \(x = 3\) and \(y = 2\).

Nitrogen as a Diatmoic Element

Nitrogen is one of a few elements that exists in a diatomic form. That is, its natural elemental form is two atoms bonded together. The Lewis Structure for elemental nitrogen, \(N_2\), is below:

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This molecule shows some very important patterns concerning nitrogen in chemical bonding: in perfectly stable molecules, every nitrogen atom will have three bonding pairs of electrons and one lone pair. Nitrogen behaves in this way in order to claim a full outer valence shell of electrons. With two electrons it keeps for itself and six that it shares with another atom, that makes eight electrons total. Thus this form of nitrogen is more stable than a single atom of nitrogen, which only has five valence electrons and must react with another chemical to become stable.

In either case, however, the oxidation number of the nitrogen atom is \(0\).

Nitrogen Oxyanions

Nitrogen also has a family of oxyanions. The two in this group are the nitrate ion, \(NO_3^{-}\), and the nitrite ion, \(NO_2^{-}\). Either of these can form acids or ionic compounds, much like nitride ions.

Example 2a:Calcium Nitrate has a chemical formula of \(Ca(NO_3)_2\). Similarly, Calcium Nitrite has a chemical formula of \(Ca(NO_2)_2\).

Example 2b:Either oxyanion of nitrogen can covalently bond with one hydrogen cation to form an acid.

Formation of nitric acid:

$$H^{+} + NO_3^{-} \rightarrow HNO_3$$

Formation of nitrous acid:

$$H^{+} + NO_2^{-} \rightarrow HNO_2$$

Other Chemicals with Nitrogen

There are a couple major chemicals with nitrogen that have not already been mentioned.

The first is azide, \(N_3^{-}\):

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Some of the nitrogen atoms have negative formal charges and some have positive formal charges. However, the total charge of the molecule is negative.

Example 3a:Being an anion, azide sometimes joins up with cations to form ionic compounds. One example is sodium azide, \(NaN_3\).

Example 3b:Azide anions can also combine with hydrogen cations to form \(HN_3\), known as azidic acid:

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There are also three other related anions that contain carbon and nitrogen: cyanide (\(CN^{-}\)), cyanate (\(CNO^{-}\)), and thiocyanate (\(CNS^{-}\)). The Lewis Structure for cyanide is shown below.

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All three of these can form ionic compounds and acids as well. Moving down the group of the periodic table containing oxygen and sulfur, we can say, in theory, that if \(CNSe^{-}\) and \(CNTe^{-}\) exist, they would essentially have the same valence-shell electron orientation as cyanate and thiocyanate. In other words, there Lewis Structures are almost identical. However, the existence of these two latter chemicals is unknown. The takeaway from this discussion is that we can use the structure of the periodic table and the knowledge of some existing chemicals to predict others that, in theory, may exist.

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Thanks to the app linked here for providing Lewis Structure images:http://www.wolframalpha.com/widgets/view.jsp?id=689aa5a01c216d8b16ed0250cebdc702.