Chemistry

Difference Between Monatomic Ions and Polyatomic Ions

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Main Difference

The main difference between Monoatomic Ions and Polyatomic Ions are that Monoatomic Ions are made up of a single atom, whereas Polyatomic Ions are made up of two or more than two types of atoms per ion.

Monoatomic Ions vs. Polyatomic Ions

Monoatomic ions are considered as ions having a single atom per ion; on the other hand, polyatomic ions are also ions made up of several atoms per ion. Monoatomic ions composed of only single atoms usually per ion; on the contrary, polyatomic ions are composed of many atoms usually per ion.

Monoatomic ions are produced by either losing or gaining electrons in the outermost shell of an atom; on the flip side, polyatomic ions are produced by the bonding between several atoms together through covalent bonds or coordinate covalent bonds. In monoatomic ions, there are presently no chemical bonds; conversely, in polyatomic ions, there are present covalent bonds or coordinate covalent bonds.

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In monoatomic ions, the monoatomic chemical species could be ions or inactive gases; on the other hand, in polyatomic ions, some polyatomic species are may be ions, and some are molecules. The popular properties of monoatomic ions are that many monoatomic ions are stable in water, very stable so chemically inactive; on the contrary, some well-known properties of polyatomic ions are many polyatomic ions are either covalently bonded or metallic complexes, electrically neutral.

The size of the monoatomic ions varies according to the functions they perform such as when positive ions are formed, their size decreases, and when the negative ions are formed, their size increases as compared to the original atom; on the other hand, the size of polyatomic ions is always bigger than all the original atoms when the polyatomic ions are formed because always two or more atoms combine to form polyatomic ions.

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According to the geometry of monoatomic ions, the monoatomic ions are spherical in their geometry, while the polyatomic ions vary in their geometry depending on the number of species and the lone pairs in the molecules because as the number of atoms increases, the more complex structure started to form to attain the stability.

Monoatomic ions consist of charge, whereas polyatomic ions consist of charge named as ‘radicals.’ The examples of monoatomic ions are Na+, K+, Cl–,, etc.; on the flip side, the examples of polyatomic ions are NH4+, NO2–, NO3–, etc.

Comparison Chart

Monoatomic IonsPolyatomic Ions
A monoatomic ion is an ion that contains a single atom, which is usually ionized.A polyatomic ion contains many atoms but acts one ion because they are bonded to each other.
Considered As
Considered as ions having a single atom per ionAlso, ions made up of several atoms per ion
Number of Atoms
Composed of only single atom usually per ionComposed of many atoms usually per ion
Formation
Produced by either losing or gaining electrons in the outermost shell of an atomProduced by the bonding between several atoms together through covalent bonds or coordinate covalent bonds
Chemical Bonding
There are presently no chemical bondsThere are present covalent bonds or coordinate covalent bonds
State
The monoatomic chemical species could be ions or inactive gasesSome polyatomic species are may be ions, and some are molecules
Properties
Many monoatomic ions are stable in water

Very stable so chemically inactive

Many polyatomic ions are either covalently bonded or metallic complexes

Electrically neutral

Size
The size varies according to the functions they perform such as when positive ions are formed, their size decreases, and when the negative ions are formed, their size increases as compared to the original atomThe size is always bigger than all the original atoms when the polyatomic ions are formed because always two or more atoms combine to form polyatomic ions
Shape
Spherical in their geometryVaries in their geometry depending on the number of species and the lone pairs in the molecules because as the number of atoms increases, the more complex structure started to form to attain the stability
Charges
Consist of chargeConsist of charge named as ‘radicals.’
Examples
Na+, K+, Cl–, etcNH4+, NO2–, NO3–, etc

What are Monoatomic Ions?

An ion consisting of exactly one atom per unit ion is known as a monoatomic ion. These atoms could be anions or cations. If some atoms make different ions by demounting valence electrons present in the outermost shell electron shells, then these ions will be known as monoatomic cations. If some ions are made by the electrons gaining from the external shell of the electron, then these ions will be referred to as monoatomic anions.

There are many elements that can form only monoatomic ions. But there are also present other elements which can form polyatomic ions as well. Monatomic ions consist of various electrical charges on the basis of the number of electrons present in their valence shell.

For example, Magnesium is present in the 2nd element group and consists of two valence electrons. When we remove these two valence electrons, mg will make mg+2 cations, and this will be a monoatomic cation.

What are Polyatomic Ions?

The ions which are composed of a cluster of atoms per unit ion are known as polyatomic ions. The polyatomic ions could be diatomic ions or triatomic ions.

There is a present infinite number of familiar polyatomic ions. Some of these polyatomic ions are present in the biological system, some are naturally occurring, or some are synthetic ions. These polyatomic ions are considered very useful.

In polyatomic ions, the atoms are bonded to each other through a covalent bond, which are sigma bonds or pi bonds. Many times, the polyatomic ion is produced as a coordination complex where central metal is surrounded by many neutrally charged ligands. These ligands are further attached to the central or main atom through coordinate or organize covalent bond and form a complex known as complex ions. The charge present on this ion is the charge of the central metal ion.

Key Differences

  1. Monoatomic ions are considered as ions that contain a single atom, while polyatomic ions are also deliberated as ions but contain a cluster of atoms.
  2. There are presently no chemical bonds in monoatomic ions, while covalent bonds or coordinate covalent bonds are present in polyatomic ions.
  3. The monoatomic ions are usually formed by the losing or gaining of electrons, which are present in the outermost shell of an atom; on the other hand, the polyatomic ions are generally formed by the bonding between several atoms thorough covalent bond or coordinate covalent bond.
  4. The size of monoatomic ions varies as sometimes their size increase when negative ions are formed, and many times the size increase when negative ions are formed; on the flip side, the size of polyatomic ions is always increased because they form by the combination of many atoms.
  5. Some examples of monoatomic ions are Na+, Ca2+, K+, Al3+, and Fe3+; conversely, many examples of polyatomic ions are CrO42-, CO32-, NH4+, H3O+.

Conclusion

The above discussion concludes that the monoatomic ions and polyatomic ions differ from each other on the base of the number of atoms present in those ions. The monoatomic ions consist of single atom per ion, whereas polyatomic ions consist of many atoms per ion.

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Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss