Copper II Oxide: Formula, Properties & Structure

Instructor: Matthew Bergstresser
Copper(II) oxide is an ionic compound consisting of copper and oxygen ions. In this lesson, we will discuss its formula, physical properties of the compound and its structure.

Natural Compound

Just under 0.007% of Earth's crust is comprised of copper. Around 46% of Earth's crust is oxygen, and just over 20% of Earth's atmosphere is oxygen. These two compounds can come together chemically to form copper(II) oxide. Let's figure out how these two elements combine and discuss the properties and structure of the compound.


The chemical combination of a metal and a non-metal generates an ionic compound. We can determine the formula for an ionic compound based on how many electrons the metal atom loses and how many electrons the non-metal atom gains. The Roman numeral II tells us the electric charge or oxidation state of the copper ion, which is +2. This means each copper atom loses two electrons to form the ion Cu+2.

Oxygen is a non-metal and will always gain two electrons giving it the oxidation state -2. Since each oxygen atom has two extra electrons, the oxide ion is formed, which is O-2.

All ionic compounds have to be electrically neutral, which means the ratio of each element in the compound must contribute enough charge to cancel the charge of the other ion. In the case of the copper(II) ion and the oxygen ion, we can see both ions have equal and opposite charges. This means we only need one of each ion to form the neutral compound copper(II) oxide, which is CuO. Let's discuss the properties of copper(II) oxide.


When you watch police television dramas you might hear them describe the characteristics of the person they are looking for. They might note their physical appearance including height, weight, eye color and so on. They also might also note their personality. Are they friendly, reserved or generally cranky? We can use this analogy to understand the types of properties of a compound including its physical characteristics and its chemical reactivity. Let's pretend we are a detective searching for the copper(II) oxide compound like we are searching for a person.

We are on the lookout for an ionic compound with the following physical characteristics:

  • Molar mass equal to 78.92 g/mole
  • Black or dark brown solid possibly in powder form
  • Density of around 6.31 g/cm3
  • Melts at just over 1200°C
  • Boils at around 2000°C

Copper(II) oxide powder

Copper(II) oxide is an amphoteric substance, which means it can act as an acid or a base. It is non-flammable and insoluble in water. Now that we know what to look for in terms of copper(II) oxides properties, let's talk about its structure.


Since copper(II) oxide is an ionic compound, the Cu+2 and the O-2 stick together due to electrostatic attraction. This type of bond is very similar to how two opposite ends of a magnet stick together, except this is on the atomic scale.

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