Question

Write formulas for the following cations: (a) potassium (h) calcium (b) ammonium (i) lead(II) (c) copper(I) (j) zinc (d) titanium(IV) (k) silver (e) nickel(III) (l) hydrogen (f) cesium (m) tin(II) (g) mercury(II) (n) iron(III)

Short answer

Formulas for the cations are: (a) K\textsuperscript{+}, (b) NH\textsubscript{4}\textsuperscript{+}, (c) Cu\textsuperscript{+}, (d) Ti\textsuperscript{4+}, (e) Ni\textsuperscript{3+}, (f) Cs\textsuperscript{+}, (g) Hg\textsuperscript{2+}, (h) Ca\textsuperscript{2+}, (i) Pb\textsuperscript{2+}, (j) Zn\textsuperscript{2+}, (k) Ag\textsuperscript{+}, (l) H\textsuperscript{+}, (m) Sn\textsuperscript{2+}, (n) Fe\textsuperscript{3+}.

Step-by-step solution

Identify the charge of each cation based on its name

For main group elements, the cation has a positive charge equal to the group number. For transition metals, the Roman numeral indicates the charge. For polyatomic cations, memorize or look up the charge.

Write the formula for each cation

Write the chemical symbol of the element followed by the charge as a superscript. If there is no charge specified for main group elements, assume a +1 charge.

Verify the correctness

Double-check that the charges written as superscripts match the common oxidation states for the elements or the specified charge in the Roman numeral.

Key concepts

Polyatomic Cations

In chemistry, polyatomic cations are charged species (ions) composed of two or more atoms covalently bonded, or of a metal complex that can be considered to behave as a single unit in the context of acid and base chemistry or in the formation of salts. Unlike monatomic cations (like those of sodium or potassium, which consist of only one atom), polyatomic cations include several atoms.

One common example is the ammonium ion (( NH_4^+ )), which is a nitrogen atom covalently bonded to four hydrogen atoms and carries an overall positive charge. When writing the formula for any cation, it’s essential to include not only the composition of the ion but also the overall charge, with the charge written as a superscript after the atomic or molecular formula.

For students, recognizing and memorizing polyatomic cations is crucial as they often appear in various chemical compounds. In the original exercise provided, ammonium (( NH_4^+ )) is a polyatomic cation, and it's important to be comfortable identifying this structure and charge to excel in chemistry.

Oxidation States

The oxidation state, often known as the oxidation number, is a concept that provides a deep insight into the electronic structure of a compound. It is a way of describing the degree of oxidation (the loss of electrons) of an atom in a chemical compound. Oxidation states are typically represented by integers, which can be positive, negative, or zero.

In the original exercise, identifying the oxidation state is the key to writing the correct formula for each cation. The oxidation state is given directly in some cases by the Roman numeral in a metal's name, for example, lead(II) ( Pb^{2+} ) or mercury(II) ( Hg^{2+} ). The oxidation state of a main group element—as seen with potassium (( K^+ )) or cesium (( Cs^+ ))—is equal to the charge of the ion, corresponding to the group number of the element on the periodic table.

Understanding and correctly identifying oxidation states is imperative in the composition of chemical formulas and in understanding redox reactions, electrochemistry, and coordination complexes.

Chemical Nomenclature

The system of chemical nomenclature is the structured set of rules for naming chemical substances. It's the linguistic bridge that allows for clear communication in the world of science, particularly chemistry. For students to master chemical nomenclature, they must familiarize themselves with the various rules that apply to different types of compounds.

For cations, the name often includes a representation of the oxidation state, especially for transition metal cations that can have multiple possible oxidation states. For example, 'iron(III)' refers to an iron ion with an oxidation state of +3 (( Fe^{3+} )). In other cases, such as for main group elements or ions with a unique possible oxidation state, the name is simply the name of the element followed by 'ion.'

In the given exercise, correct application of chemical nomenclature is critical for identifying the right charge to formulate each cation. Understanding and practicing the rules of chemical nomenclature allows students to both name compounds from their formulas and to write chemical formulas based on the name of the compounds.