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Metal Oxide

In periodic table more 75% of elements are metallic in nature such as gold, silver, platinum, mercury, uranium, aluminum, sodium and calcium. Metals are placed on the left side of periodic table. Group 1 to 12 includes alkali metal, alkaline earth metal and transition metals. At the bottom of periodic table again there are some metallic elements called as lanthanides and actinides.

Generally, metals are shiny solids having high melting points and densities. They have maximum atomic radius in their period. Due to this they have low ionization potential and low electronegativity. Due to their malleable and ductile properties of metal, they can be deformed without breaking and drawn into wire. Because of low ionization potential, they can easily lose electron and good conductor of heat and electricity.

Metals can combine with other metal and non-metal to form alloys which are widely used in many industries. Metals can form halides, oxide, carbonate, nitride and other compound with suitable reagent.

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Metal Oxide Definition

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"The metallic compounds which are formed with metal and oxygen in the form of oxide ion (O2-) are called as metal oxide."

They named in two words where first word is the name of metal with oxidation number in parenthesis followed by oxide. 

Metal (Oxidation number) Oxide

The formula of metal oxide has to be written in two words; first write the symbol of first element with oxidation number than write symbol of oxygen O with an oxidation number -2. At last calculate the fewest atoms of each element. 

Metallic oxides are basic in nature and often exist as solids at room temperature. Generally, metal oxides are insoluble in water and produce salts with acids. Like reaction of magnesium oxide with hydrochloric acid forms magnesium chloride.

MgO + 2HCl $\to$ MgCl2 + H2O

Some metal oxides are acidic or amphoteric in nature and form salts with base in neutralization reaction. For example, aluminum oxide reacts with sodium hydroxide to form sodium aluminate. Those metallic oxides which have oxygen-oxygen bond are known as peroxides. Here oxygen atom presents in -1 oxidation state. 

Some common examples of metallic peroxides are as follow.

Peroxide Table

Transition Metal Oxide

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Below Point Explain about Transition Metal Oxide:-
  1. d-block elements are placed from group-3 to group-12 in periodic table. These all are metallic in nature and also known as transition metals.
  2. Since in these metals, the valence shell electrons are located in d-orbital and are loosely bound and contribute to high electrical conductivity of the transition metals.
  3. Like other metals, they have low ionization potential and show a wide range of oxidation state. Due to variable oxidation states of transition metals, they can form many type of compounds.
  4. The oxidation number of transition metals is increases in period from left to right than reaches to maximum and decreases at the end of series.
  5. This is because as we move from left to right in series, number of unpaired d-electrons increases till middle than electrons get paired.
  6. The highest oxidation state of a transition metal is equal to sum of number of unpaired d-electron and number of electrons in s-orbitals that is two.
  7. For example in first transition series, 3d-series form scandium to zinc, number of unpaired electrons increases till manganese than decrease.
The oxidation states of 3d-series transition metals are as follows.

Electronic Configuration Table
Due to variable oxidation states of transition metals, they can form various oxides in different oxidation states. In oxides, oxygen stabilizes the highest oxidation state of transition metals. Till group-7, the highest oxidation state is same as the group number like Sc2O3 to Mn2O7. From group-8 to group-12, the maximum oxidation state is +3 like in Fe2O3.

In oxo-cations, transition metals exist in their maximum oxidation state like vanadium (V) in VO2+ and titanium (IV) in TiO2+. Transition metal oxides are widely used as catalyst and semiconductors. 

Non Metal Oxide

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The oxides of non-metals are composed of non-metals and oxygen in form of oxide ion (O2-). They are named in two words where first word is of non-metal with Greek prefix which shows the number of atoms and second word will be oxide. Greek prefix of non-metal oxides are as follow.

Some of the common non-metal oxides with their names are as follow.

Non Metal Oxides
Non-metal oxides are either acidic or amphoteric in nature and generally exist in gaseous state at room temperature like carbon dioxide, carbon monoxide, sulfur dioxide etc. Some of non-metallic oxides like carbon monoxide, carbon dioxide, nitric oxide are neutral in nature. These oxides react with water to form acids, like sulfur trioxide reacts with water and produces sulfuric acid.

SO3 + H2O $\to$ H2SO4

Similarly carbon dioxide reacts with water to form carbonic acid

CO2 + H2O $\to$ H2CO3

The reaction of non-metallic oxides with base or alkali forms salts. Like reaction of carbon dioxide with sodium hydroxide gives sodium carbonate.

CO2 + NaOH $\to$ Na2CO3

Metal Oxide Water

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Metallic oxides are basic in nature and form hydroxides with water. Metal hydroxides are strong base. This is a combination reaction and can be reversed by the action of heat; therefore metal hydroxide decomposes on heating to form metal oxide and water. Alkali metal oxides react vigorously in water to form hydroxides like reaction of quick lime (CaO) with water forms slaked lime (Ca(OH)2).

CaO + H2O Ca(OH)2

Some common examples of metal oxide in water are as follow.

Na2O +H2O NaOH
MgO + H2O Mg(OH)2
Fe2O3 + H2OFe(OH)2
ZnO + H2O Zn(OH)2
Al2O3 + H2OAl(OH)2

Metal Oxide Semiconductor

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Metal oxide semiconductor consists of three components, a metal electrode, a silicon substrate and an insulating film of silicon dioxide. The metal layer is conducting in nature, while middle layer is an insulator of glass or silicon dioxide, and the bottom layer is another conductive layer composed of crystal silicon and acts as semiconductor whose conductivity can changes with doping and temperature.


These semiconductors are used in capacitors, diode, transistor etc. For example: in Metal oxide semiconductor capacitor is composed of a semiconductor substrate with a thin oxide layer and a metal layer called as gate. The second layer is known as bulk contact.

Now in an ideal metal oxide semiconductor biased with positive or negative voltages, three possibilities may exist at the semiconductor surface
  1. Accumulation: when one applies a voltage which is less than flat band voltage, accumulation occurs on surface. In that case; negative charge on gate attracts the holes to metal oxide semiconductor surface.
  2. Depletion: If the external voltage is more positive compare to flat band voltage, depletion occurs and a negative charge is builds up on semiconductor.
  3. Inversion: If the potential across the semiconductor is more than the bulk potential, a negative potential creates at metal oxide semiconductor interface and form an inversion layer.
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