Problem 34 - Chemistry Matter and Change

Question

State the order in which the ions associated with a compound composed of potassium and bromine would be written in the chemical formula and the compound name.

Step-by-Step Solution

Answer

The ions of a compound composed of potassium and bromine should be written in the chemical formula as \(KBr\), with the potassium ion (K+) first and the bromine ion (Br-) second. The compound name is potassium bromide, naming the cation first followed by the anion with an -ide suffix.

Step 1: Identify the elements and their charges

Potassium is an alkali metal in Group 1 of the periodic table and has a +1 charge (K+). Bromine is a halogen in Group 17 of the periodic table and has a -1 charge (Br-).

Step 2: Construct the chemical formula

For an ionic compound to be electrically neutral, the positive and negative charges must be equal. In this case, the potassium ion (K+) and bromine ion (Br-) simply combine 1:1 to form the compound potassium bromide, with its chemical formula being KBr.

Step 3: Write the compound name

The compound name consists of the name of the cation (positively charged ion) followed by the name of the anion (negatively charged ion) with an -ide suffix. In this case, the cation is potassium (K+), and the anion is bromide (Br-). Thus, the compound name is potassium bromide.

Step 4: Final answer

The ions associated with the compound composed of potassium and bromine should be written in the chemical formula as KBr, and the compound name is potassium bromide.

Key Concepts

Ionic Compounds

Ionic compounds are a class of chemical compounds formed by the electrostatic attraction between positively and negatively charged ions. These ions are atoms or molecules that have gained or lost electrons, resulting in a net positive or negative charge.
When forming ionic compounds, metals typically lose electrons to become positively charged cations, while non-metals gain electrons to become negatively charged anions.

• Metals, located on the left side of the periodic table, form cations.
• Non-metals, found on the right side, form anions.

In an ionic bond, the total positive charge must equal the total negative charge to achieve electrical neutrality. This leads to the simple integer ratios often seen in ionic compounds, like the 1:1 ratio in potassium bromide (KBr), where a potassium ion bonds with a bromide ion.

Potassium Bromide

Potassium bromide, with the chemical formula KBr, is a classic example of an ionic compound. In this compound, potassium (K) acts as the cation, and bromine (Br) serves as the anion.
Potassium, an alkali metal, readily loses one electron to form a positively charged ion (K⁺). Bromine, a halogen, gains one electron to form a negatively charged ion (Br^-).

• The +1 charge of potassium perfectly complements the -1 charge of bromine.
• These opposite charges attract each other, resulting in the formation of a stable ionic compound.

The chemical formula KBr reflects the stoichiometry of the compound, indicating a 1:1 ratio of potassium to bromine, while the name "potassium bromide" clearly identifies the cation and anion involved.

Periodic Table

The periodic table is a fundamental tool in chemistry that organizes chemical elements based on their properties. It helps predict how elements will interact, providing insight into the formation of ionic compounds.
Potassium is located in Group 1, known as the alkali metals, which are characterized by their single electron in the outer shell. This makes them very reactive and predisposed to forming +1 cations. Bromine is in Group 17, known as the halogens, which have seven electrons in their outer shell, making them highly reactive as well and likely to form -1 anions.

• Elements in the same group share similar chemical behaviors.
• The periodic table's layout predicts the type and number of ions formed by each element.

Understanding the periodic table is crucial for writing chemical formulas and names of compounds like potassium bromide (KBr) because it elucidates the ion charges and pairing possibilities.