Question

Give the systematic names for the formulas or the formulas for the names: (a) \(\mathrm{CoO}\); (b) mercury(I) chloride; (c) chromic oxide; (d) \(\mathrm{CuBr}_{2}\).

Short answer

(a) cobalt(II) oxide (b) \(\mathrm{Hg_2Cl_2}\) (c) \(\mathrm{Cr_2O_3}\) (d) copper(II) bromide

Step-by-step solution

- Name the compound \(\text{CoO}\)

The given compound is \(\mathrm{CoO}\). \(\text{Co}\) stands for cobalt, and the \(\text{O}\) is oxygen. Since cobalt has multiple oxidation states, determine the charge on \(\text{O}\) which is \(-2\). Therefore, cobalt must be \(+2\) here to balance it. The systematic name is cobalt(II) oxide.

- Write the formula for mercury(I) chloride

Mercury(I) chloride indicates that mercury is in the \(\text{+1}\) oxidation state. Since mercury(I) exists as \(\text{Hg}_2^{2+}\), each mercury ion has a charge of \(\text{+1}\). Chloride ion has a charge of \(\text{-1}\). Therefore, two chloride ions are needed to balance \(\text{Hg}_2^{2+}\). The formula is \(\text{Hg}_2Cl_2\).

- Name the compound chromic oxide

Chromic oxide is another name for chromium(III) oxide. Chromium is in the \(\text{+3}\) oxidation state and oxide is \(-2\). To balance the charges, the formula must be \(\text{Cr}_2O_3\).

- Name the compound \(\mathrm{CuBr_2}\)

The given compound is \(\text{CuBr}_2\). \(\text{Cu}\) stands for copper, and \(\text{Br}_2\) stands for two bromide ions. Each bromide ion is \(-1\), so the total negative charge is \(\text{-2}\). Therefore, copper must be \(\text{+2}\). The systematic name is copper(II) bromide.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, indicate the degree of oxidation of an atom in a chemical compound. They help in determining the charge of atoms, especially for elements that can exist in multiple oxidation states, like transition metals. For example, cobalt in \(\text{CoO}\) has an oxidation state of \(+2\) to balance oxygen's \(-2\) charge. Cobalt can have other oxidation states too, such as \(+3\), but here, it’s important we balance the charges correctly to establish cobalt's \(+2\). This concept is crucial for naming compounds systematically and ensuring we have the correct formula.

Polyatomic Ions

Polyatomic ions are ions that consist of more than one atom. They often contain oxygen and other elements. For instance, the ion \(\text{Hg}_2^{2+}\) in mercury(I) chloride is a polyatomic ion with a \(+2\) overall charge, meaning each mercury atom carries a partial \(+1\) charge. They play a vital role in the composition of many inorganic compounds. Understanding polyatomic ions and their charges help us in correctly writing chemical formulas. For example, in \(\text{Hg}_2Cl_2\), two chloride ions, each with a \(-1\) charge, balance the \(+2\) charge of the mercury(I) dimer.

Nomenclature in Inorganic Chemistry

Nomenclature in inorganic chemistry deals with naming inorganic compounds following systematic rules. This process helps to avoid confusion and provides specific information about the compound's composition. When naming a compound like \(\text{CuBr}_2\), where copper is paired with two bromide ions, we determine that copper's oxidation state must be \(+2\). Therefore, the name 'copper(II) bromide' specifies not only the elements but their respective oxidation states. This precision in naming ensures effective communication in the scientific community.

Chemical Formulas

Chemical formulas represent the types and numbers of atoms in a compound. They are fundamental in writing and interpreting chemical equations. For example, the formula \(\text{Cr}_2O_3\) tells us that chromic oxide consists of two chromium atoms and three oxygen atoms. Knowing these formulas allows us to understand the compound's properties and reactions. Writing the formula involves identifying the correct ratios based on the charges of the ions, ensuring the compound is electrically neutral. For instance, in \(\text{Cr}_2O_3\), chromium is \(+3\) and oxygen is \(-2\), balancing to form a neutral compound.

Transition Metals

Transition metals are elements found in the d-block of the periodic table. They are known for having multiple oxidation states and forming complex ions. This characteristic can sometimes make naming and determining formulas slightly more intricate. In the compound \(\text{CoO}\), cobalt is a transition metal with an oxidation state of \(+2\). Transition metals also often appear in various compounds and can form brightly colored solutions or solids. Identifying the specific oxidation state of a transition metal is key to correctly naming the compound and understanding its chemical behavior. For instance, \(\text{CuBr}_2\) involves copper in the \(+2\) oxidation state, highlighting the varied chemistry of transition metals.