Question

What is the oxidation state of nitrogen in the following compounds? (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{N}_{2} \mathrm{H}_{4}\) (c) \(\mathrm{N}_{2} \mathrm{O}\) (d) \(\mathrm{NO}_{2}\)

Short answer

(a) -3, (b) -2, (c) +1, (d) +4

Step-by-step solution

Identify the total oxidation state of the molecule

Determine that for neutral molecules, the sum of the oxidation states of all the atoms is zero. For ions, it might instead equal the charge of the ion.

Assign known oxidation states

Assign oxidation states to other elements in the compound according to known rules: Hydrogen is usually +1, and Oxygen is usually -2.

Solve for nitrogen in NH3

In \( ext{NH}_3\), assign +1 to hydrogen. Since there are three hydrogens, the total contribution is +3. Therefore, the oxidation state of nitrogen is calculated as +X (nitrogen) + 3(+1) = 0 \rightarrow X = -3.

Solve for nitrogen in N2H4

In \( ext{N}_2 ext{H}_4\), hydrogen contributes +1 per atom. For the four hydrogens, the total is +4. Let X be the oxidation state of nitrogen: 2X + 4(+1) = 0 \rightarrow 2X = -4 \rightarrow X = -2. So, each nitrogen has an oxidation state of -2.

Solve for nitrogen in N2O

In \( ext{N}_2 ext{O}\), oxygen typically has an oxidation state of -2. To balance the compound to zero, let the oxidation state of each nitrogen be represented as X: 2X + (-2) = 0 \rightarrow 2X = +2 \rightarrow X = +1. Thus, each nitrogen has an oxidation state of +1.

Solve for nitrogen in NO2

In \( ext{NO}_2\), oxygen's oxidation state is -2, contributing a total of -4. Let X be the oxidation state of nitrogen: X + 2(-2) = 0 \rightarrow X - 4 = 0 \rightarrow X = +4.

Key concepts

Nitrogen Compounds

Nitrogen compounds are chemical substances that contain nitrogen atoms. Nitrogen is an element that can combine with many other elements to form a variety of compounds. Some of these are naturally occurring while others are synthetic. Here are some examples of nitrogen compounds:

• Ammonia (\(\mathrm{NH}_{3}\)).
• Hydrazine (\(\mathrm{N}_{2} \mathrm{H}_{4}\)).
• Nitrous Oxide (\(\mathrm{N}_{2} \mathrm{O}\)).
• Nitrogen Dioxide (\(\mathrm{NO}_{2}\)).

These compounds have varying properties based on the elements they bond with and the structure of their molecules. For example, ammonia is a colorless gas with a pungent smell, whereas nitrogen dioxide is a reddish-brown gas with a sharp, biting odor. Understanding the chemistry of these compounds often involves calculating the oxidation states of nitrogen in each molecule. This helps to determine how electrons are distributed among atoms in the compound, which in turn affects their chemical behavior.

Chemical Bonds

Chemical bonds are the attractive forces that hold atoms together in molecules and compounds. In the context of nitrogen compounds, these bonds are essential for maintaining the structure and stability of the compound. There are three primary types of chemical bonds:

• Ionic bonds: Formed between metals and non-metals, where electrons are transferred from one atom to another, resulting in ions.
• Covalent bonds: Involves the sharing of electron pairs between atoms. For example, in ammonia (\(\mathrm{NH}_{3}\)), nitrogen shares electrons with hydrogen through covalent bonds.
• Metallic bonds: Consists of a lattice of positively charged ions and delocalized electrons, typical of metallic elements.

No metallic bonds are present in nitrogen compounds like the ones we are discussing. Instead, covalent bonds primarily maintain the compounds, affecting properties such as solubility, melting points, and reactivity. Understanding these bonds is essential for predicting how nitrogen compounds interact with other substances in chemical reactions.

Oxidation Numbers

Oxidation numbers, also known as oxidation states, are a way of keeping track of how many electrons an element has gained, lost, or shared when forming compounds. This concept is crucial in understanding the reactivity and functionality of different compounds.For nitrogen-containing compounds, calculating the oxidation numbers helps you determine the overall charge distribution:

• In \(\mathrm{NH}_{3}\), nitrogen's oxidation state is \(-3\), as determined by assigning \(+1\) to each hydrogen.
• In \(\mathrm{N}_{2} \mathrm{H}_{4}\), each nitrogen has an oxidation state of \(-2\).
• In \(\mathrm{N}_{2} \mathrm{O}\), nitrogen exhibits an oxidation state of \(+1\).
• Finally, in \(\mathrm{NO}_{2}\), nitrogen's oxidation state is \(+4\).

Assigning oxidation numbers helps interpret how electrons are distributed in a compound, aids in balancing chemical equations, and informs about the potential redox behavior of the compound. When determining these numbers, remember there are rules: like hydrogen generally being \(+1\) and oxygen typically \(-2\), unless in peroxides or bonded to fluorine. This allows chemists to predict reactions and the possible creation of new compounds.