Question

Why do we call \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) barium nitrate but call \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) iron(II) nitrate?

Short answer

The difference in naming arises due to the existence of multiple oxidation states in the elements involved. For a compound like \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\), Barium has only one common oxidation state (+2), so we simply use its name combined with Nitrate. However, for a compound like \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), Iron has multiple oxidation states. To differentiate between these states, we use Roman numerals indicating the oxidation state, in this case +2, resulting in the name iron(II) nitrate.

Step-by-step solution

Understand the nomenclature for compounds with elements having only one oxidation state:

In a compound like \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\), Barium is an alkaline earth metal that has only one common oxidation state, which is +2. Since there's no ambiguity in the type of Barium compound, we just use the name of Barium (element) + Nitrate (polyatomic anion). Therefore, the name is barium nitrate.

Understand the nomenclature for compounds with elements having multiple oxidation states:

In a compound like \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), Iron is a transition metal that can have different oxidation states, such as +2 and +3. To differentiate between the different states, we use Roman numerals, which are placed in parentheses immediately after the element's name. The numeral indicates the positive oxidation state of the element.

Determine the oxidation state of element and name the compound:

In \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), we can use the nitrate ion to determine the oxidation state of Iron. The nitrate anion NO\(_{3}^{-}\) has a charge of -1. Since there are two nitrate ions in the compound, the negative charge will be -2. Therefore, the oxidation state of Iron must be +2 to balance the charges. So, we will call this compound iron(II) nitrate.

Key concepts

Oxidation States

Understanding oxidation states is crucial when studying chemical reactions and naming compounds. An oxidation state, also known as an oxidation number, represents the degree of oxidation (loss of electrons) of an atom in a chemical compound. It is a theoretical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. The oxidation state can be an integer or a fraction.

For simple ions, the oxidation state is equal to the charge of the ion. For example, sodium ions (a ^+) have an oxidation state of +1, while chloride ions (cl^-) have an oxidation state of -1. However, things get more complicated with covalent substances and polyatomic ions. In such cases, the oxidation states of atoms are often determined by following a set of rules, where the sum of oxidation states of all atoms in a molecule or compound must equal the charge of the molecule or ion.

These rules include: assigning an oxidation state of +1 to hydrogen (except when hydrogen forms compounds with metals where it is -1), -2 for oxygen (with exceptions), and using known oxidation states for metals wherever possible. When an element can have more than one possible oxidation state, as is the case with many transition metals like iron (Fe), the correct oxidation state is indicated in the compound name with Roman numerals.

Transition Metals

Transition metals are the elements found in the center of the periodic table, specifically in groups 3 through 12. They are unique for their ability to exhibit a wide range of oxidation states, which is due to the unfilled d-electron subshells in their electron configurations. This characteristic can lead to complex chemical behavior, especially with regard to their compounds and interactions with other elements.

Iron (Fe), for example, commonly has two prevalent oxidation states, +2 and +3, thus leading to iron(II) and iron(III) compounds. Unlike alkaline earth metals, such as barium (Ba), which typically exhibit only one oxidation state, the versatility of the transition metals requires a more detailed naming convention to reflect their specific chemical properties.

The presence of different oxidation states leads to a wide array of possible compounds and is responsible for the colorful nature of many transition metal compounds. In nomenclature, the oxidation state of a transition metal in a chemical compound is specified using Roman numerals in parentheses after the metal name.

Polyatomic Ions

Polyatomic ions consist of two or more atoms covalently bonded together that carry a net charge. Because they contain multiple atoms, they can have complex structures and chemistry. Polyatomic ions play crucial roles in the chemistry of solutions and the formation of crystalline salts.

For instance, nitrate (NO_3^-) is a polyatomic ion consisting of one nitrogen atom and three oxygen atoms, carrying a -1 charge. When naming compounds with polyatomic ions, the ion's name is used as-is, regardless of the oxidation state of the metal it is bonded to. This contrasts with individual elements like transition metals, whose names are specified with oxidation states to prevent ambiguity.

Understanding polyatomic ions is also essential for balancing chemical equations and predicting the solubility of compounds. As they are charged species, polyatomic ions attract and bond with ions of opposite charge, forming stable ionic compounds such as barium nitrate (Ba(NO_3)_2) where the positive charge of barium (+2) balances the negative charge of two nitrate ions (-1 each).