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Polyatomic Compounds

We know that atoms have tendency to bond with same or different atoms with the help of their valence electrons. The valence electrons are placed in the outermost shell of an atom. Atoms can share or transfer their valance electrons to form a chemical bond. On the basis of sharing or transfer of valence electrons, chemical bonds can be two types; covalent bond and ionic bond. Ionic bonds are electrostatic force of attraction between two oppositely charged ions; cation and anion. 

On the contrary, covalent bond is formed by the sharing of valance electrons of bonded atoms. Atoms tend to get the octet configuration and for that they form covalent bond or ions to form ionic bond. Atoms combine to form molecules. If different types of atoms combine, they form compounds such as combination of hydrogen and oxygen results the formation of water. The ionic compounds are formed by the combination of cations and anions. For example sodium ion and chloride ions combine to form ionic compounds; sodium chloride. Ions which are formed by more than one atom are called as polyatomic ions. 

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Polyatomic Compounds Definition

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Polyatomic compounds can be defined as the compounds which are formed by polyatomic ions.  For example oxyanions are negatively charged polyatomic ions with oxygen can combine with cation to form polyatomic compounds. Some other examples of polyatomic ions are $ClO_4^{-}$(perchlorate), $ClO_{3}^{-}$ (chlorate), $ClO_{2}^{-}$ (chlorite) and $ClO$- (hypochlorite) etc. Some other polyatomic ions are listed bvelow;

List of Polyatomic Ions

Naming Polyatomic Compounds

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For the naming of polyatomic compounds, we have to learn the naming of polyatomic ions. The name of polyatomic compounds consists of two parts; cation and anion. Either cation or anion would be polyatomic in nature. The name cation will be followed by the name of anion such as potassium dichromate or hydrogen carbonate. Some other polyatomic compounds with their names are listed below.

Naming Polyatomic Compounds


Polyatomic Compounds List

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Polyatomic compounds consist of polyatomic cation or anion. Hence we can say that they are ionic compounds with polyatomic ions. The naming and properties of polyatomic compounds are very much same as of ionic compounds. Name of cation is followed by name of anion in naming of polyatomic compound. Here cation or anion, anyone can be polyatomic in nature. Some of the polyatomic compounds are listed below;

Polyatomic Compounds List


Polyatomic Compounds Examples

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The polyatomic ions are usually written in parenthesis and number of atoms must be written as subscript. Name of $Fe(NO_{3})_{2}$  would be ferrous nitrate. This is because; $NO_{3}$ is a polyatomic ion with 1- charge over it. Since there are two NO3-1 ions therefore the oxidation state of Fe must be 2- that is ferrous ion. Hence the name of this polyatomic compound can be written as Iron(II) nitrate or ferrous nitrate. Similarly name of NaOH would be sodium hydroxide. Here sodium is 1+ ion with hydroxide ion OH 1-. Here hydroxide ion is a polyatomic ion as it consists of one oxygen atom and one hydrogen atom. And the name of compound would be sodium hydroxide. Similarly $KMnO_{4}$ consists of one potassium ion with 1+ charge and one polyatomic ion MnO4¯ which is named as permanganate ion. Hence the name of give polyatomic compound would be potassium permanganate. Another example of polyatomic compound is $Cu_{2}SO_{4}$ which contains two copper ions and one polyatomic ion that is sulphate ion. The oxidation state of copper in this compound is Cu(I) hence the name of compound would be Copper(I) sulphate or cuprous sulphate. Here 2 as subscript after Cu indicates that there are two copper ions which balance the 2- charge of sulphate ion which is a polyatomic ion.

Polyatomic Compounds Formulas

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The formula writing of polyatomic compound also follows some common rules such as name of cation is followed by name of anion. The oxidation state of metal must be written in parenthesis as Roman number. The name of polyatomic anion will end with suffix ‘ide’ or ‘ate’. For example formula of calcium chlorate would be $Ca(ClO_{3})_{2}$. For the formula writing of this compound you must know the formula or structure of chlorate ion that is $ClO_{3}^{1-}$. Since calcium is an alkaline earth metal and usually exist as $Ca^{2+}$ ion, therefore for balancing the charges of cation and anion, the formula would be  $Ca(ClO_{3})_{2}$. Some other formulae of polyatomic compounds with their names are listed below;

Polyatomic Compounds Formulas
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