Problem 134 - Chemistry An Atoms First Approach

Question

The designations \(1 \mathrm{A}\) through \(8 \mathrm{A}\) used for certain families of the periodic table are helpful for predicting the charges on ions in binary ionic compounds. In these compounds, the metals generally take on a positive charge equal to the family number, while the nonmetals take on a negative charge equal to the family number minus \(8 .\) Thus the compound between sodium and chlorine contains \(\mathrm{Na}^{+}\) ions and \(\mathrm{Cl}^{-}\) ions and has the formula NaCl. Predict the formula and the name of the binary compound formed from the following pairs of elements. a. Ca and N b. \(K\) and 0 c. \(\mathrm{Rb}\) and \(\mathrm{F}\) d. \(\mathrm{Mg}\) and \(\mathrm{S}\) e. Ba and I f. Al and Se g. Cs and \(P\) h. In and Br

Step-by-Step Solution

Answer

The binary ionic compounds formed from the given pairs of elements are: a. Calcium nitride (Ca\(_3\)N\(_2\)) b. Potassium oxide (K\(_2\)O) c. Rubidium fluoride (RbF) d. Magnesium sulfide (MgS) e. Barium iodide (BaI\(_2\)) f. Aluminum selenide (Al\(_2\)Se\(_3\)) g. Cesium phosphide (Cs\(_3\)P) h. Indium bromide (InBr\(_3\))

Step 1: Identify the charges of the elements

Ca is in family 2A, so it will have a charge of +2. N is in family 5A, so it will have a charge of -3 (5-8 = -3).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 3 Ca ions and 2 N ions. The formula will be Ca\(_3\)N\(_2\)

Step 3: Name the compound

The compound will be named Calcium nitride. b. K and O

Step 1: Identify the charges of the elements

K is in family 1A, so it will have a charge of +1. O is in family 6A, so it will have a charge of -2 (6-8 = -2).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 2 K ions and 1 O ion. The formula will be K\(_2\)O

Step 3: Name the compound

The compound will be named Potassium oxide. c. Rb and F

Step 1: Identify the charges of the elements

Rb is in family 1A, so it will have a charge of +1. F is in family 7A, so it will have a charge of -1 (7-8 = -1).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 1 Rb ion and 1 F ion. The formula will be RbF.

Step 3: Name the compound

The compound will be named Rubidium fluoride. d. Mg and S

Step 1: Identify the charges of the elements

Mg is in family 2A, so it will have a charge of +2. S is in family 6A, so it will have a charge of -2 (6-8 = -2).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 1 Mg ion and 1 S ion. The formula will be MgS.

Step 3: Name the compound

The compound will be named Magnesium sulfide. e. Ba and I

Step 1: Identify the charges of the elements

Ba is in family 2A, so it will have a charge of +2. I is in family 7A, so it will have a charge of -1 (7-8 = -1).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 1 Ba ion and 2 I ions. The formula will be BaI\(_2\).

Step 3

The compound will be named Barium iodide. f. Al and Se

Step 1: Identify the charges of the elements

Al is in family 3A, so it will have a charge of +3. Se is in family 6A, so it will have a charge of -2 (6-8 = -2).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 2 Al ions and 3 Se ions. The formula will be Al\(_2\)Se\(_3\).

Step 3

The compound will be named Aluminum selenide. g. Cs and P

Step 1: Identify the charges of the elements

Cs is in family 1A, so it will have a charge of +1. P is in family 5A, so it will have a charge of -3 (5-8 = -3).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 3 Cs ions and 1 P ion. The formula will be Cs\(_3\)P.

Step 3

The compound will be named Cesium phosphide. h. In and Br

Step 1: Identify the charges of the elements

In is in family 3A, so it will have a charge of +3. Br is in family 7A, so it will have a charge of -1 (7-8 = -1).

Step 2: Create the formula for the compound

To create the compound, we need to balance the charges by having 1 In ion and 3 Br ions. The formula will be InBr\(_3\).

Step 3

The compound will be named Indium bromide.

Key Concepts

Understanding Binary Ionic Compounds

A binary ionic compound is formed by the combination of two different elements, typically one metal and one nonmetal. These compounds consist of ions that have opposite charges, which attract each other to form a neutral compound.

The metal atoms lose electrons to form cations, positively charged ions, while the nonmetal atoms gain electrons to become anions, negatively charged ions. For instance, sodium (Na), from family 1A in the periodic table, loses one electron to form a Na⁺ ion, and chlorine (Cl), from family 7A, gains an electron to become Cl^- ion. When combined, they create the binary ionic compound sodium chloride (NaCl).

It's vital for students to understand that the compound overall must be electrically neutral. That means the total positive charge from the metal cations must balance out the total negative charge from the nonmetal anions. This principle guides us in determining the correct formula for a binary ionic compound.

Predicting Ion Charges from the Periodic Table

The periodic table is like a roadmap for understanding the charges ions are likely to have. Elements are organized into groups or families, and each group has a common charge trend for its ions. Generally, elements in group 1A will lose one electron and form ions with a +1 charge, and as we move to group 2A, they form ions with a +2 charge, and so forth.

On the other hand, nonmetals, typically starting from group 5A, tend to gain electrons to achieve a full outer shell. For example, nitrogen (N) from group 5A will gain three electrons to form N^3- and oxygen (O) from group 6A will gain two electrons to become O^2-.

Tips for Predicting Charges:

• Check the element's group number if it's a metal for positive charges.
• For nonmetals, subtract the group number from 8 to determine their negative charge.
• Remember that transition metals can have multiple charges and are not as predictable as group 1A to 3A elements.

These guidelines help students predict charges correctly and balance them when forming binary ionic compounds.

The Art of Chemical Formula Naming

Naming chemical formulas correctly is crucial for clear communication in science. The name of a binary ionic compound includes the name of the metal (cation) first, followed by the name of the nonmetal (anion) with its ending changed to 'ide'.

To master the naming, you'll often need to recognize the charges on the ions involved to ensure that you are using the correct ratio in the name. For example, Magnesium Sulfide implies a compound of Mg²⁺ and S^2- ions, correctly combined in a 1:1 ratio to maintain charge neutrality as MgS.

Key Naming Rules:

• When the metal has more than one possible charge, a Roman numeral in parentheses indicates its charge.
• Monoatomic anions end in 'ide' — hence, chlorine becomes chloride in NaCl.
• For polyatomic ions, use the name of the ion directly as it appears on common ion lists (e.g., nitrate for NO₃^-).

With practice, remembering these rules and applying them systematically will become second nature for students learning chemical nomenclature.