Problem 38 - Chemistry The Molecular Nature of Matter

Question

The other major air pollutant is \(\mathrm{NO}_{2}\). What are the oxidation numbers of the atoms in \(\mathrm{NO}_{2} ?\)

Step-by-Step Solution

Answer

The oxidation number of nitrogen in \(\mathrm{NO}_{2}\) is +4, and the oxidation number of each oxygen is -2.

Step 1: Understanding the concept of oxidation numbers

Oxidation numbers represent the charge an atom would have if electrons were completely transferred. They can be useful in understanding the degree of oxidation or reduction of an atom in a compound. In a molecule, the sum of all oxidation numbers must equal the overall charge of the molecule.

Step 2: Assign oxidation numbers based on known values

For the compound \(\mathrm{NO}_{2}\), we know that oxygen generally has an oxidation number of -2. Since there are two oxygen atoms, their total oxidation number is -4.

Step 3: Calculate the oxidation number of nitrogen

The compound \(\mathrm{NO}_{2}\) is neutral, so the sum of the oxidation numbers must be zero. We can set up an equation where the oxidation number of nitrogen (let's call it 'x') plus the total oxidation number of oxygen (-4) equals zero: \[ x + (-4) = 0 \]Solve for x to find the oxidation number of nitrogen.

Step 4: Solve for the oxidation number of nitrogen

By adding 4 to each side of the equation from Step 3, we get \[ x = +4 \]The oxidation number of nitrogen in \(\mathrm{NO}_{2}\) is +4.

Key Concepts

Chemical Oxidation States

Understanding chemical oxidation states is essential when studying chemistry, especially when dealing with redox reactions. An oxidation state, also known as an oxidation number, is a theoretical charge on an atom. It's a bookkeeping method that helps chemiles track electron movement in chemical reactions. When atoms form chemical bonds, they can either lose, gain, or share electrons. The oxidation state is a way of expressing the degree of loss or gain of electrons.

In the provided example involving nitrogen dioxide (o{NO_2}), the oxidation state of oxygen is typically -2 as oxygen usually gains two electrons. To find the oxidation number of nitrogen, we use a simple algebraic method considering that the molecule is neutral. Hence, the sum of oxidation numbers of all atoms in o{NO_2} should equal zero. This concept is not just a mere arithmetic exercise; it enhances the understanding of how atoms stabilize themselves through various bond formations, a core part of understanding chemical reactions.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are processes where electron transfer occurs between two chemical species. The element that loses electrons undergoes oxidation, and the element that gains electrons undergoes reduction. These reactions are fundamental to numerous biological processes, energy production, and even the formation of many substances.

A deep understanding of redox reactions hinges on comprehension of oxidation states. By determining the changes in oxidation numbers, one can identify which elements are being oxidized and reduced in the reaction process. For instance, in a hypothetical scenario where o{NO_2} is involved in a redox reaction, the oxidation state of +4 for nitrogen can help predict the possible reactions it can undergo, like being reduced to a lower oxidation state.

Chemical Bonding

Chemical bonding pertains to the force that holds atoms together in molecules. Atoms bond to achieve a more stable electron configuration. There are mainly three types of bonds: ionic, covalent, and metallic. Ionic bonding happens when there is a complete transfer of electrons from one atom to another, leaving behind a positively charged cation and a negatively charged anion. For example, although o{NO_2} does not form ionic bonds as it is a non-metal molecule, understanding ionic character is crucial when examining what oxidation numbers suggest about electron distribution in other contexts.

The oxidation numbers in the context of chemical bonding can signify if the electrons are equally shared (covalent bonding) or if there's an electron transfer (ionic bonding). In o{NO_2}, the bonds between nitrogen and oxygen have covalent character with some degree of ionic character due to the difference in electronegativity, clarifying that oxidation states can also offer insights into bond nature.

Molecular Compounds

Molecular compounds are composed of two or more nonmetals with atoms bonded covalently. These compounds, such as o{NO_2}, exhibit specific properties such as low melting points, and low boiling points, and are often poor conductors of electricity. Oxidation numbers in molecular compounds are particularly useful to denote the hypothetical charges that atoms would have if all bonds were ionic. The calculation of oxidation states, as demonstrated with the nitrogen dioxide molecule, can reveal important information about the structure and reactivity of the molecule.

Recognizing that nitrogen has an oxidation state of +4 allows us to predict possible chemical reactions involving o{NO_2}, such as reactions with water to form acid rain. It also shows us that in molecular compounds, while atoms share electrons, the sharing is not necessarily equal—one atom often exerts more electronegativity over the shared electrons, as can be implied from their oxidation state.