Question

Which of the following are correct formulas for ionic compounds? For those that are not, give the correct formula. (a) \(\mathrm{AlCl}_{2}\) (b) \(\mathrm{KF}_{2}\) (c) \(\mathrm{Ga}_{2} \mathrm{O}_{3}\) (d) MgS

Short answer

(a) \(\mathrm{AlCl}_3\), (b) \(\mathrm{KF}\), (c) \(\mathrm{Ga}_2\mathrm{O}_3\), (d) \(\mathrm{MgS}\).

Step-by-step solution

Identify Cation and Anion Charges

For each compound, identify the charges of the cation and anion. Aluminum (\( \mathrm{Al} \)) has a charge of \(+3\), Chlorine (\( \mathrm{Cl} \)) has a charge of \(-1\). Potassium (\( \mathrm{K} \)) has a charge of \(+1\), Fluorine (\( \mathrm{F} \)) has a charge of \(-1\). Gallium (\( \mathrm{Ga} \)) has a charge of \(+3\), Oxygen (\( \mathrm{O} \)) has a charge of \(-2\). Magnesium (\( \mathrm{Mg} \)) has a charge of \(+2\), Sulfur (\( \mathrm{S} \)) has a charge of \(-2\).

Check for Charge Neutrality

Verify that the formulas result in charge neutrality. - (a) \(\mathrm{AlCl}_2\): \(3 \times (+1) + 2 \times (-1) = +1\) so not neutral.- (b) \(\mathrm{KF}_2\): \(1 \times (+1) + 2 \times (-1) = -1\) so not neutral.- (c) \(\mathrm{Ga}_2\mathrm{O}_3\): \(2 \times (+3) + 3 \times (-2) = 0\) so neutral.- (d) \(\mathrm{MgS}\): \(1 \times (+2) + 1 \times (-2) = 0\) so neutral.

Determine Correct Formulas

For compounds that are not neutral, find the correct ratio to balance charges.- (a) For \(\mathrm{AlCl}_2\), correct formula is \(\mathrm{AlCl}_3\) because \(1 \times (+3) + 3 \times (-1) = 0\).- (b) For \(\mathrm{KF}_2\), correct formula is \(\mathrm{KF}\) because \(1 \times (+1) + 1 \times (-1) = 0\).

Compile Result

Based on the calculations:- (a) Incorrect, should be \(\mathrm{AlCl}_3\).- (b) Incorrect, should be \(\mathrm{KF}\).- (c) Correct.- (d) Correct.

Key concepts

Chemical Formulas

When we talk about chemical formulas, we are describing the way that elements are combined in compounds. Each formula conveys important details, such as how many of each type of atom are present in the compound.

These formulas are built using symbols from the periodic table and subscripts to indicate the number of atoms. For example, in the formula \(\mathrm{H}_2\mathrm{O}\), there are two hydrogen atoms and one oxygen atom. For ionic compounds, this formula needs to reflect the balance of different ions that come together to form the compound.

The key is to accurately represent the way atoms bond together, which usually involves a balance of charges for ionic compounds, as you'll see in the next sections.

Charge Neutrality

Charge neutrality is an essential concept in chemistry, particularly when dealing with ionic compounds. A compound is charge-neutral when the total positive charge from the cations (positively charged ions) equals the total negative charge from the anions (negatively charged ions).

Why is charge neutrality important? Well, it ensures that the compound is stable and complete. If the charges aren't balanced, as seen in incorrect formulas like \(\mathrm{AlCl}_2\), the compound wouldn't exist in reality as described.

To achieve neutrality, you often need to adjust the subscripts in a chemical formula. This means figuring out the right number of each ion needed to balance out the charges. For example, if you have a \(+3\) cation and \(-1\) anions, you will need three anions to balance one cation.

• This balance is essential for writing correct chemical formulas.
• It reflects the real-world stability of ionic compounds.

Cation and Anion Charges

In ionic compounds, the charges of cations and anions are crucial. They determine how the ions will combine to form a stable compound. Understanding these charges is key to writing correct chemical formulas.

Cations are positively charged ions, typically metals like aluminum (\(\mathrm{Al}^{3+}\)) or magnesium (\(\mathrm{Mg}^{2+}\)). Anions carry a negative charge and are usually non-metals, such as chlorine (\(\mathrm{Cl}^{-}\)) or oxygen (\(\mathrm{O}^{2-}\)).

• Cations are formed when an atom loses one or more electrons.
• Anions are formed when an atom gains one or more electrons.

By knowing the charge on each ion, you can determine how many of each are needed to form a neutral ionic compound. This counting is what leads to the sometimes complex-seeming formulas.

Balancing Chemical Equations

Balancing chemical equations goes hand in hand with writing chemical formulas, particularly for ionic compounds. This process ensures that the number of atoms for each element is the same on both sides of a chemical equation, conserving mass. It's not just about getting the right numbers, but also ensuring that the chemistry works, reflecting charge neutrality and correct stoichiometry.

Let's consider balancing equations as setting the stage for a chemical reaction. If we start with the incorrect formulas, the planned reaction won't proceed as expected. When dealing with ionic formulas, understanding the charges can help you figure out the right ratios.

• Balancing involves adjusting coefficients, never changing the formulas of the chemical compounds themselves.
• It ensures both mass and charge conservation in a reaction.

Writing and balancing chemical equations require careful attention to detail but following the rules of chemistry makes it straightforward.