Question

Name the compounds in parts a-d and write the formulas for the compounds in parts e-h. a. \(\mathrm{NaBr}\) b. \(\mathrm{Rb}_{2} \mathrm{O}\) c. CaS d. \(\mathrm{AlI}_{3}\) e. strontium fluoride f. aluminum selenide g. potassium nitride h. magnesium phosphide

Short answer

The compounds in parts a-d are named as follows: a. Sodium bromide b. Rubidium oxide c. Calcium sulfide d. Aluminum iodide The formulas for the compounds in parts e-h are: e. SrF2 (strontium fluoride) f. Al2Se3 (aluminum selenide) g. K3N (potassium nitride) h. Mg3P2 (magnesium phosphide)

Step-by-step solution

Identify elements and their oxidation states

For the given compounds, we'll identify the elements involved in each compound, and their standard oxidation states. The oxidation state is the charge on the ion when it forms a compound. a. NaBr Na (Sodium) has an oxidation state of +1. Br (Bromine) has an oxidation state of -1. b. Rb2O Rb (Rubidium) has an oxidation state of +1. O (Oxygen) has an oxidation state of -2. c. CaS Ca (Calcium) has an oxidation state of +2. S (Sulfur) has an oxidation state of -2. d. AlI3 Al (Aluminum) has an oxidation state of +3. I (Iodine) has an oxidation state of -1.

Name the compounds a-d

Now that we know the elements and their oxidation states, we can name the compounds as follows: a. Sodium bromide b. Rubidium oxide c. Calcium sulfide d. Aluminum iodide

Write the formulas for the compounds e-h

Now we'll identify the elements and their oxidation states for the given compounds and write their formulas based on those values: e. Strontium fluoride Sr (Strontium) has an oxidation state of +2. F (Fluoride) has an oxidation state of -1. So, the formula is SrF2. f. Aluminum selenide Al (Aluminum) has an oxidation state of +3. Se (Selenium) has an oxidation state of -2. So, the formula is Al2Se3. g. Potassium nitride K (Potassium) has an oxidation state of +1. N (Nitrogen) has an oxidation state of -3. So, the formula is K3N. h. Magnesium phosphide Mg (Magnesium) has an oxidation state of +2. P (Phosphorus) has an oxidation state of -3. So, the formula is Mg3P2.

Key concepts

Naming Ionic Compounds

The naming of ionic compounds is a fundamental aspect of chemical nomenclature. It involves identifying the positive and negative ions within a compound and applying specific rules to create its name. For monatomic ions, the cation (positive ion) retains the element's name, while the anion (negative ion) is named by taking the element's root and adding the suffix -ide.

For example, in the compound \( \mathrm{NaBr} \), sodium (Na) is the cation and bromine (Br) is the anion. Following the naming rules, the compound is called sodium bromide. In compounds like \( \mathrm{Rb}_{2}\mathrm{O} \), we name it rubidium oxide because rubidium takes the cation role and oxygen becomes oxide as the anion.

Transition Metals and Variable Oxidation States

When dealing with transition metals that can have multiple oxidation states, a Roman numeral is used in parentheses to indicate the cation's oxidation state. However, for the compounds in our exercise, we don't encounter this scenario because all the metals involved have only one common oxidation state in their respective compounds.

Oxidation States

Oxidation states, also known as oxidation numbers, represent the hypothetical charges that atoms would have if the compound was composed of ions. These numbers are essential for naming compounds and writing formulas because they help determine the ratio of ions in the compound.

In each ionic compound, the sum of the oxidation states must equal zero because the compounds are electrically neutral. For example, in \( \mathrm{CaS} \), calcium has a +2 oxidation state and sulfur a -2. The equal but opposite charges cancel out, resulting in a neutral compound. Similarly, for \( \mathrm{AlI}_{3} \), the aluminum cation has a +3 oxidation state and each iodine anion has a -1 state, requiring three iodine ions to balance the charge of one aluminum ion.

Utilizing the Periodic Table

To determine an element's common oxidation state, one can often refer to the periodic table as a guide. Group 1 elements typically have a +1 oxidation state, while Group 2 elements have a +2. Transition metals may vary, and Group 17 elements (halogens) commonly have a -1 oxidation state, except when bonded with oxygen or other halogens.

Chemical Formulas

Chemical formulas encapsulate the elemental composition of a substance, providing the types of atoms present and their relative proportions. For ionic compounds, the formula is dictated by the need for charge balance between the positively charged cations and the negatively charged anions.

In the chemical formula for strontium fluoride, \( \mathrm{SrF}_{2} \), the subscript '2' indicates that two fluoride ions, each with a -1 charge, combine with one strontium ion with a +2 charge to maintain overall neutrality. The formula for aluminum selenide, \( \mathrm{Al}_{2}\mathrm{Se}_{3} \), reveals a ratio of two aluminum ions to three selenium ions, balancing the +3 and -2 charges, respectively.

Empirical and Molecular Formulas

It's crucial to differentiate between empirical and molecular formulas. The empirical formula represents the simplest whole-number ratio of elements in the compound, while the molecular formula shows the actual number of atoms in a molecule. For ionic compounds, which don't contain discrete molecules, the chemical formula is typically the empirical formula, representing the smallest ratio of ions in the crystal lattice structure.