Question

Assign charges to the oxygen-containing anions in the following compounds: (a) \(\mathrm{Li}_{2} \mathrm{O}\) (b) \(\mathrm{K}_{2} \mathrm{O}_{2}\) (c) \(\mathrm{CsO}_{2}\)

Short answer

(a) -2, (b) -1, (c) -0.5 per oxygen atom.

Step-by-step solution

Assign Charges Based on Common Oxidation States

Identify the typical oxidation states of the elements involved. Lithium (Li), potassium (K), and cesium (Cs) are alkali metals with a common oxidation state of +1. Oxygen has several common oxidation states, -2 being most common, but can also be -1 or -0.5 depending on the compound.

Determine Charge for Li2O

In the compound \(\mathrm{Li}_{2} \mathrm{O} \), lithium has a charge of +1. There are 2 lithium atoms, contributing a total charge of +2. Therefore, to balance the charges, oxygen must have a charge of -2.

Determine Charge for K2O2

In \(\mathrm{K}_{2} \mathrm{O}_{2} \), two potassium atoms each with a charge of +1 contribute a total of +2. To balance this, the two oxygen atoms together must have a charge of -2. This means each oxygen atom has a charge of -1, indicating a peroxide anion.

Determine Charge for CsO2

In \( \mathrm{CsO}_{2} \), the cesium atom has a charge of +1. The compound must be neutral overall, so the total charge from two oxygen atoms is -1. This indicates each oxygen has a charge of -0.5, signifying it is a superoxide anion.

Key concepts

Anion Charges

In chemistry, anions are negatively charged ions. They gain electrons to achieve this negative charge, opposite to cations that lose electrons and become positive. Understanding anion charges is essential to determine the composition and reactivity of different compounds.

Anion charges are dictated by the oxidation state of the element. If you examine oxygen, its most common oxidation state is -2. When oxygen gains two electrons, it typically forms an oxide anion (O)\[-2\]. However, in certain compounds like peroxides and superoxides, oxygen can have oxidation states of -1 or -0.5 respectively.

Being able to assign the correct charge to anions helps in predicting the kind of reactions a compound will undergo. It also directs how to balance chemical equations. Remember, the sum of the charges in a stable compound must be zero, and knowing the anion charges is a crucial step in achieving this balance.

Balancing Charges

Balancing charges in a compound is like maintaining a scale where both sides need to be equal. The goal is to have the total positive charge equaled by the total negative charge. For example, in \(\mathrm{Li}_2\mathrm{O}\), two lithium ions each contribute a +1 charge, summing to +2 overall. Oxygen, with an oxidation state of -2 balances this perfectly.

Let's look at another scenario. In \(\mathrm{K}_2\mathrm{O}_2\) (potassium peroxide), two \(\text{K}^+\) ions provide +2, while each oxygen contributes -1, for a total negative charge of -2 from the peroxide anion (O\(-\)). This maintains the neutrality of the compound.

In balancing charges, consider:

• Each alkali metal typically offers a +1 charge.
• The total of positive and negative charges must be zero for the compound to be stable.

Balancing is a fundamental principle that helps chemists confirm the correctness of chemical formulas and the feasibility of reactions.

Alkali Metals

Alkali metals are elements found in Group 1 of the periodic table. This group includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). They are characterized by having a single electron in their outermost shell, which they readily lose to achieve a stable electronic configuration, resulting in a +1 charge.

Due to their single valence electron, alkali metals are highly reactive, especially with nonmetals like oxygen. For instance, in compounds such as \(\mathrm{Li}_2\mathrm{O}\) and \(\mathrm{K}_2\mathrm{O}_2\), the alkali metal's +1 charge plays a key role in determining the structure and properties of the compound.

Some important points about alkali metals include:

• They are very reactive and must be stored without any moisture.
• Reactions involving alkali metals are usually exothermic.
• They form ionic compounds with nonmetals.

Understanding the behavior of alkali metals can help in predicting how they interact in different chemical processes.

Oxygen Oxidation States

Oxygen is a versatile element with several possible oxidation states, leading to diverse chemical behavior. The typical oxidation state of oxygen is -2, which is found in most compounds like water (H\_2\O) and oxides.

However, oxygen can exhibit other oxidation states in different types of compounds:

• Peroxides: Here, oxygen has an oxidation state of -1. Examples are hydrogen peroxide (\(\mathrm{H}_2\mathrm{O}_2\)) and potassium peroxide (\(\mathrm{K}_2\mathrm{O}_2\)).
• Superoxides: In these rare compounds, oxygen has an oxidation state of -0.5. This occurs in compounds such as cesium superoxide (\(\mathrm{CsO}_2\)).
  
  

Understanding oxygen's oxidation states is crucial because it helps to predict the type of oxygen species present in a compound, which consequently affects the compound's reactivity and stability. Knowing these states aids in balancing equations and understanding redox reactions in depth.