Difference Between Metal Oxides and Non Metal Oxides

Main Difference – Metal Oxides vs Non Metal Oxides

An oxide is any chemical compound that contains one or more oxygen atoms. Metals are substances that have unique properties such as excellent electrical and thermal conductivity, reflectivity of light, malleability and ductility. Metals form a wide variety of compounds such as metal halides, metal oxides, metal sulfides, etc. Nonmetals are chemical elements that fail to show metallic properties. Most members of the p block in the periodic table are nonmetals. When considering the oxides of elements, there are metal oxides as well as non metal oxides. Metal oxides are oxides of metals. Nonmetal oxides are oxides of nonmetals. The main difference between metal oxides and non metal oxides is that metal oxides are basic compounds whereas nonmetal oxides are acidic compounds.

Key Areas Covered

1. What are Metal Oxides
     – Definition, Properties, Different Types
2. What are Non Metal Oxides
     – Definition, Properties, Different Types
3. What is the Difference Between Metal Oxides and Non Metal Oxides
     – Comparison of Key Differences

Key Terms: Acid, Base, Metal, Metal Oxide, Nonmetal, Nonmetal Oxide, Oxyacids, Oxide, Peroxide, Superoxide 

What are Metal Oxides

Metal oxides are chemical compounds containing a metal and one or more oxygen atoms. Here, the oxidation number of oxygen is -2, and it is essentially the anion where metal is the cation. Alkali metals (group 1 elements), alkaline earth metals (group 2 elements) and transition metals (some d block elements) form ionic oxides. But metals showing high oxidation states can from oxides with a covalent nature.

Metal oxides are crystalline solid compounds. These compounds contain a metal cation and an oxide anion. These compounds are often basic compounds and can react with water giving a base. If not, they can react with acids forming a salt of the metal.

There are three types of metal oxides formed alkali metals and alkaline earth metals.

1. Oxides containing oxide anions (O^2-)
2. Peroxides containing peroxide anions (O^–)
3. Superoxides containing superoxide anions. (O₂^–)

The number of oxygen atoms that bind with the metal ion depends on the oxidation number of the metal ion. Alkali metals form only monovalent cations. Therefore, they form only M₂O type oxides (where M is the metal ion and O is oxide anion). Alkaline earth metals form divalent cations. Therefore, they form MO type cations.

Figure 1: Rare Earth Oxides – Clockwise from Top Center: Praseodymium, Cerium, Lanthanum, Neodymium, Samarium, and Gadolinium Oxides

Both alkali and alkaline earth metal oxides form hydroxides when reacted with water. Therefore, they are basic compounds. D block elements form different oxides depending on the oxidation state. For example, Vanadium show oxidation states +2, +3, +4 and +5. Hence, the oxides it can form are VO, V₂O, VO₂ and V₂O₅.

What are Non Metal Oxides

Nonmetal oxides are oxide compounds formed by nonmetal elements. Most p block elements are nonmetals. They form various oxide compounds. Nonmetal oxides are covalent compounds since they share electrons with oxygen atoms to form oxide molecules.

Most nonmetal oxides give acids after reacting with water. Therefore, nonmetal oxides are acidic compounds. For example, when SO₃ is dissolved in water, it gives H₂SO₄ solution, which is highly acidic. Nonmetal oxides react with bases to form salts.

Figure 2: Some Reactions of Nonmetals with Oxygen

Nonmetal oxides can form oxyacids. Oxyacids yield hydronium ions in aqueous solutions. There are two types of acidic oxides:

1. Acid anhydrides whose nonmetal exhibits one of its most common oxidation state such as in N2O5, SO3.
2. Acid oxides whose nonmetal does not exhibit its most common oxidation states. Ex: NO₂, ClO₂.

Difference Between Metal Oxides and Non Metal Oxides

Definition

Metal Oxides: Metal oxides are chemical compounds containing a metal and one or more oxygen atoms.

Non Metal Oxides: Nonmetal oxides are oxide compounds formed by nonmetal elements.

Nature

Metal Oxides: Metal oxide are basic compounds.

Non Metal Oxides: Nonmetal oxides are acidic compounds.

Reaction with Water

Metal Oxides: Metal oxides react with water, forming basic solutions.

Non Metal Oxides: Nonmetal oxides react with water, forming acidic solutions.

Structure

Metal Oxides: Metal oxides are ionic compounds. But metal oxides with higher oxidation state meta cations have a  covalent nature.

Non Metal Oxides: Nonmetal oxides are covalent compounds.

Reaction with Acids and Bases

Metal Oxides: Metal oxides react with acids, forming salts.

Non Metal Oxides: Nonmetal oxides react with bases, forming salts.

Conclusion

Metal oxides are compounds composed of metal ions and oxide ions. Nonmetal oxides are compounds composed of nonmetal atoms and oxygen atoms. The main difference between metal oxides and non metal oxides is that metal oxides are basic compounds whereas nonmetal oxides are acidic compounds.

References: 

1. “Metal Oxides.” Chemistry LibreTexts, Libretexts, 3 Nov. 2016, Available here.
2. Zumdahl, Steven S. “Oxide.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 13 Feb. 2014, Available here.

Image Courtesy:

1. “Rareearthoxides” By Peggy Greb, US department of agriculture –  (Public Domain) via Commons Wikimedia
2. “Gr 9 – Ch 4 – Reactions of non-metals with oxygen” by Siyavula Education (CC BY 2.0) via Flickr