Question

Give the formula and name for each ionic compound formed between the two listed ions. a) \(\mathrm{K}^{+}\) and \(\mathrm{S}^{2-}\) b) \(\mathrm{Ag}^{+}\) and \(\mathrm{Br}^{-}\) c) \(\mathrm{Sr}^{2+}\) and \(\mathrm{N}^{3-}\)

Short answer

a) \\mathrm{K_{2}S\\}, potassium sulfide; b) \\mathrm{AgBr\\}, silver bromide; c) \\mathrm{Sr_{3}N_{2}\\}, strontium nitride.

Step-by-step solution

Identifying Charges for Potassium Sulfide

Potassium ion is \(\mathrm{K}^{+}\), with a charge of +1, and sulfide ion is \(\mathrm{S}^{2-}\), with a charge of -2. We need two potassium ions to balance the charge of one sulfide ion.

Writing Chemical Formula for Potassium Sulfide

To balance the charges, use two potassium ions for each sulfide ion, resulting in the formula \(\mathrm{K_{2}S}\). The name of this compound is potassium sulfide.

Identifying Charges for Silver Bromide

Silver ion is \(\mathrm{Ag}^{+}\), with a charge of +1, and bromide ion is \(\mathrm{Br}^{-}\), with a charge of -1. The charges are already balanced.

Writing Chemical Formula for Silver Bromide

Since both ions have a single charge that balances each other, the chemical formula is simply \(\mathrm{AgBr}\). This compound is named silver bromide.

Identifying Charges for Strontium Nitride

Strontium ion is \(\mathrm{Sr}^{2+}\), with a charge of +2, and nitride ion is \(\mathrm{N}^{3-}\), with a charge of -3. To balance these charges, use cross-multiplication.

Writing Chemical Formula for Strontium Nitride

Cross-multiplication results in needing three strontium ions to balance two nitride ions, giving the formula \(\mathrm{Sr_{3}N_{2}}\). This compound is called strontium nitride.

Key concepts

Chemical Formulas

Understanding chemical formulas is crucial as it helps in identifying what elements are present in a compound and how many atoms of each element there are. Chemical formulas of ionic compounds are specifically structured to represent the ratio of ions without showing their actual charges. In an ionic compound, elements are represented by their chemical symbols followed by subscripts indicating the number of atoms when more than one is present.

For instance, in potassium sulfide \( \mathrm{K_2S} \), there are two potassium (\( \mathrm{K} \)) ions for every one sulfide (\( \mathrm{S} \)) ion, suggesting a simple yet informative compound representation. Here, the removal of the charges ensures that the formula remains neutral overall. Similarly, in silver bromide \( \mathrm{AgBr} \), both ions have equal and opposite charges, so the formula represents one atom of each element forming the compound. In strontium nitride \( \mathrm{Sr_3N_2} \), three strontium ions are needed to balance the charge of two nitride ions.

Chemical formulas reflect the empirical ratio of ions in a compound, ensuring neutrality without indicating molecular compositions as seen in molecular compounds. This neat representation aids in quick understanding and acknowledgment of the compound's elemental constitution.

Balancing Charges

Balancing charges is an essential principle when writing formulas for ionic compounds. Ionic balances ensure that compounds remain neutral, meaning that the positive and negative charges from the ions must cancel each other out. Imagine having a balance scale; you place positive ions on one side and negative ions on the other. The scale must be balanced for the compound to be stable.

Here's how to approach the process:

• Identify the charges of each ion involved. For example, potassium \( \mathrm{K}^{+} \) has a +1 charge, while sulfide \( \mathrm{S}^{2-} \) has a -2 charge.
• Use multiples of each ion to ensure that the sums of the charges are zero.
• The formula is built by adding the number of each type of ion needed to balance the charges.

For potassium sulfide \( \mathrm{K_2S} \), two \( \mathrm{K}^+ \) ions (totalling +2) are needed to balance one sulfur ion \( \mathrm{S}^{2-} \) with -2.
In the case of strontium and nitride, the charges \( \mathrm{Sr}^{2+} \) and \( \mathrm{N}^{3-} \) are balanced through cross-multiplication, giving the chemical formula \( \mathrm{Sr_{3}N_{2}} \). This balance keeps the ionic compound neutral, which is fundamental to the stability of chemical structures.

Ionic Bonding

Ionic bonding is the force that holds ions together in an ionic compound. This type of bonding occurs when electrons are transferred from one atom to another, typically a metal to a non-metal. The transfer creates ions – atoms with a net electric charge due to the loss or gain of electrons. The resultant attraction between positively and negatively charged ions forms an ionic bond.

Here's the detailed process:

• The metal atom loses one or more electrons, resulting in a positively charged ion (cation). For example, \( \mathrm{K} \) (potassium) loses one electron, becoming \( \mathrm{K}^+ \).
• The non-metal atom gains these electrons, resulting in a negatively charged ion (anion). So, sulphur \( \mathrm{S} \) gains two electrons, becoming \( \mathrm{S}^{2-} \).

These oppositely charged ions attract each other strongly, resulting in the formation of a stable ionic compound such as \( \mathrm{K_2S} \). The characteristic of ionic compounds is that they form a crystal lattice structure when in solid form, where ions are held in place by this electrostatic attraction.
Ionic bonding is significant because it explains the high melting and boiling points of ionic compounds, as well as their ability to conduct electricity when molten or dissolved in water. Understanding ionic bonds helps explain many physical properties and reactions in chemistry.