Oxides, Peroxides, and Superoxides - Online Tutor, Practice Problems & Exam Prep

Oxides, peroxides, and superoxides are binary compounds of oxygen with metals, categorized by their oxygen count and charge. Oxides (O₂⁻) form with group 1A and 2A metals, while peroxides (O₂²⁻) and superoxides (O₂⁻) are formed primarily by specific group 1A metals. Memory aids help recall which metals form which compounds: "peroxides are bananas" for barium and sodium, and "smart kangaroo reads comics" for potassium, rubidium, and cesium. Understanding these relationships is crucial for predicting compound formation.

Oxide, Peroxide, and Superoxide Formulas

Now oxides, peroxides and superoxides are binary compounds of oxygen with metals. Now here we're going to say that group 1A and 2A metals combined directly with oxygen to form these three types of compounds. So let's take a closer look at oxides, peroxides and superoxides.

The memory tool that we can use here is that oxides, peroxides and superoxides are 1221. So what exactly do we mean by that? Well, first of all, oxides, peroxide, superoxides, OPS. Remember, remember it in that order. And remember it's alphabetical as well. We're going to say here that the one here tells us the number of oxygen, so we have one oxygen and the second number gives us the charge. So two here would be two minus. And we know what's minus because all of these are anions.

So coming back down here, the first number gives us the number of oxygens, the second number gives us the charge. Let's move over to peroxides. Peroxides. Its first number is this 2 now, so there's two oxygens. The second number gives us its charge 2 minus, so peroxides are O2⁻2. Superoxides. The first number gives us the number of oxygens, which is 2 oxygens. The second number gives us its charge -1. So superoxide is O2⁻.

So these are the formulas for our oxides, peroxides and superoxides. Remember OPS written in alphabetical order. First number represents the number of oxygen, second number represents the charge for each of them. If you can remember that, you remember the structures of each one of these anions.

Oxides, Peroxides, And Superoxides Example

Here it says write a formula for sodium peroxide. Well, we know sodium is in Group 1A, so it's plus one in charge. But peroxide? What does peroxide look like? Well, OPS oxides, peroxides, superoxides. And we know that it has a number of 1221 peroxide which is P.

Here, remember the first number tells us the number of oxygens which is 2 and the second number tells us the charge 2 minus. So this is the formula for peroxide. The numbers in the charges are different so they don't cancel out the crisscross. One comes here, 2 comes here. So sodium peroxide would be Na2O2.

This would be our final answer.

Classify each of the following compounds as an oxide, peroxide, or superoxide.

i) Li₂O          _____________________

ii) RbO₂       _____________________

iii) BaO₂      _____________________

iv) SrO        _____________________

• A. i) superoxide
  ii) oxide
  iii) peroxide
  iv) superoxide
• B. i) superoxide
  ii) peroxide
  iii) oxide
  iv) superoxide
• C. i) peroxide
  ii) superoxide
  iii) oxide
  iv) peroxide
• D. i) oxide
  ii) peroxide
  iii) superoxide
  iv) oxide
• E. i) oxide
  ii) superoxide
  iii) peroxide
  iv) oxide

Type of Binary Compound

Now that we know what oxide peroxides and superoxides are, it's important to understand which group 18 elements, which group 28 elements create oxides, peroxides or superoxides. So we're going to say here as we go up the group, the ability to form peroxides and superoxides decreases. Group 2A metals do not form superoxides.

If we take a look here, we have our group 1A and 2A elements. We have our oxides which are in this kind of like pinkish color, our peroxide which are blue and then our brownish colors are superoxides. We can see here that lithium is in the pinkish purplish color, so it could form oxides. So lithiums in Group 1A, so it's plus one. Remember that oxides have an O2- charge, so this would be ally to O peroxides.

Here we have sodium which is in Group 1A, so plus one Peroxides are O22-, so this could be NA₂O₂. And then superoxides. Let's see, we have rubidium here. Well, we have Cessium here, which is +1. Superoxides are O2-, so this would be CSO₂. All right, so we know from this list what can make what. But how do we remember?

Well, here we have our memory tool. Our memory tool number one is peroxides are bananas. So here if we take a look and actually we're going to color code them better, peroxides are bananas, barium, sodium, those are the two elements that can make peroxides. And then here Memory Tool #2, Smart Kangaroos read comics.

So here Memory Tool two is for our superoxides. Who do we have? Kangaroo is potassium reeds is rubidium comics. C and then S, that's Cessium. Those make our super oxides. And then anything that's not part of Memory Tool One or Memory Tool 2. So basically, our oxides, they're the ones that are leftover and they're in this pinkish, purplish color, right?

So that's how we're going to remember which elements do what. So peroxides are bananas. Only barium and sodium make peroxides. Smart Kangaroos read, while smart kangaroo reads comics, potassium rubidium, cessium. They're the ones who make superoxides, cause reading is super and then everything else is an oxide. So just keep that in mind when you're asked to determine the type of oxygen compound you make when you're given a particular group 1A or 2A element.

Oxides, Peroxides, And Superoxides Example

Here it says complete and balance the following equation. We have barium solid reactant when oxygen gas. All right. So we have to remember what type of structure does barium make. If we recall memory tool #1, peroxides are bananas. Barium makes peroxides when reacting with oxygen gas.

So bariums in Group 2A. So it's two plus in charge. And then remember, what's the formula for peroxide? O2^-2 this is 2+, this is 2-. They have the same numbers in their charges, so they just cancel out and what's left behind comes together. So barium peroxide would be BA,O2. It would be a solid.

If we look, our equation is also already balanced. We have one barium on each side and two oxygens on each side. So this would be our final complete imbalance chemical reaction.

Write a balanced equation for the reaction of potassium with oxygen.

• A. K(s) + O₂(g)  KO₂(s)
• B. 2 K(s) + O₂(g)  K₂O₂(s)
• C. 2 K(s) + O₂(g)  2 KO(s)
• D. 4 K(s) + O₂(g)  2 K₂O(s)

Oxides, Peroxides, and Superoxides Summary

So here we have a summary of the reactions with oxides, peroxides and superoxides. Oxides are O2- when dealing with group 1A. Remember group 1A metals are plus one. Oxide is 2 minus like we have here. The numbers are different so one comes here and two comes here. So this would be M2O solid. To balance it, I'd have to throw a 2 here and a four here.

When reacting with group 2A we have M2+ because group two way metals are two plus and then O2-. This would just be MO solid. We put a 2 here and A2 here. Remember looking at the periodic table, our peroxides are what are in these purple pinkish boxes. Peroxides memory tool. One tells me that peroxides are bananas, so that's barium and sodium that make these types of structures.

Group 1A would be again plus one, and then we have O22-, 1 comes here, 2 comes here. So we have M2O2. We put a two year to balance it out, and then we'd have barium, which is the metal technically here, but here we'd say it's M2+O22-. The charges cancel out, and that's how we get MO2.

And then remember, memory Tool 2 Smart Kangaroo reads comics potassium rubidium cessium. They're the ones who make superoxides. So here we'd have M+1 for the group 1A metals, O2-1 charges cancel out and that's how we get MO2 solid. We don't have superoxides for group 2A, at least under normal conditions. We have to do some extraordinary things in order to force this to happen. That's beyond the scope of this course, so don't worry about that.

All right? So just remember how we learn what oxides, peroxides and superoxides are, and then remember your two memory tools to recall who are the peroxides and who are the superoxides. Everything else would just be an oxide.

Here’s what students ask on this topic:

What are the differences between oxides, peroxides, and superoxides?

Oxides, peroxides, and superoxides are binary compounds of oxygen with metals. The key differences lie in their formulas and charges. Oxides have the formula O₂^2-, peroxides are O₂^2-, and superoxides are O₂^-. In oxides, each oxygen atom has a -2 charge, while in peroxides, the two oxygen atoms share a -2 charge, resulting in each oxygen having a -1 charge. In superoxides, the two oxygen atoms share a -1 charge, giving each oxygen a -0.5 charge. These differences affect their chemical properties and reactivity.

Which Group 1a and 2a elements form oxides, peroxides, and superoxides?

Group 1a and 2a elements react with oxygen to form oxides, peroxides, and superoxides. Group 1a elements like lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs) can form these compounds. Specifically, lithium forms oxides (Li₂O), sodium forms peroxides (Na₂O₂), and potassium, rubidium, and cesium form superoxides (KO₂, RbO₂, CsO₂). Group 2a elements like barium (Ba) and sodium (Na) form peroxides, while other Group 2a elements typically form oxides (e.g., MgO, CaO). Group 2a metals do not form superoxides under normal conditions.

How do you remember which elements form peroxides and superoxides?

Memory tools can help recall which elements form peroxides and superoxides. For peroxides, use the phrase 'peroxides are bananas,' indicating that barium (Ba) and sodium (Na) form peroxides. For superoxides, use 'smart kangaroos read comics,' where 'smart' stands for potassium (K), 'kangaroos' for rubidium (Rb), and 'comics' for cesium (Cs). These mnemonics help remember that Ba and Na form peroxides, while K, Rb, and Cs form superoxides. Elements not included in these memory tools typically form oxides.

What is the formula for oxides, peroxides, and superoxides with Group 1a metals?

The formulas for oxides, peroxides, and superoxides with Group 1a metals are based on balancing the charges between the metal cations and oxygen anions. For oxides, the formula is M₂O, where M represents a Group 1a metal (e.g., Li₂O for lithium oxide). For peroxides, the formula is M₂O₂ (e.g., Na₂O₂ for sodium peroxide). For superoxides, the formula is MO₂ (e.g., KO₂ for potassium superoxide). These formulas ensure that the charges between the metal cations and oxygen anions are balanced.

Why do Group 2a metals not form superoxides under normal conditions?

Group 2a metals do not form superoxides under normal conditions due to their higher charge density and stronger electrostatic interactions. These metals have a +2 charge, which makes it energetically unfavorable to stabilize the O₂^- anion found in superoxides. The formation of superoxides requires specific conditions that are beyond the scope of typical reactions involving Group 2a metals. Therefore, under normal conditions, Group 2a metals primarily form oxides (MO) and peroxides (M₂O₂).