Ions are charged species possessing an unequal number of protons and electrons. Positively charged ions are called cations, while negatively charged ions are referred to as anions.
Cations have a deficiency of electrons, while anions possess an excess of electrons. Additionally, ions can be classified into monoatomic, polyatomic, and complex ions.
⇒ Monoatomic ions are formed by the loss or gain of electrons by a single atom only. For instance, the sodium (Na+) ion is a monoatomic cation, while the chloride (Cl–) ion is a monoatomic anion.
⇒ Polyatomic or molecular ions comprise two or more atoms covalently bonded together, possessing a net charge. Hydronium (H3O+) and carbonate (CO32-) are examples of polyatomic ions.
⇒ Complex ions possess a metal atom or ion at the center, which is surrounded by electron-donating species called ligands via coordinate covalent bonds; for instance, [Fe(NH3)6]2+ is a complex cation.
What do you think, are all the different types of ions introduced above polar or non-polar?
Don’t worry, through this article; we will find out in detail, whether ions are polar or non-polar. So, continue reading!
Are ions polar or non-polar?
Ions can be either polar or non-polar.
Monoatomic ions are generally non-polar in nature as they possess a spherical shape and, thus, a symmetrical charge distribution.
The polarity of polyatomic ions depends upon the constituent species and their arrangement, i.e., the molecular shape of the ion.
Below are some examples of monatomic, polar and non-polar polyatomic ions.
Non-polar monoatomic ions
Non-polar polyatomic ions
Polar polyatomic ions
Sodium (Na+)
Phosphate (PO43-)
Dihydrogen phosphate (H2PO4–)
Potassium (K+)
Carbonate (CO32-)
Hydronium (H3O+)
Magnesium (Mg2+)
Sulfate (SO42-)
Chlorate (ClO3–)
Calcium (Ca2+)
Ammonium (NH4+)
Chlorite (ClO2–)
Oxide (O2-)
Nitrate (NO3–)
Nitrite (NO2–)
Hydrogen ion (H+)
Borate (BO33-)
Sulfite (SO32-)
Hydride (H–)
Manganate (MnO42-)
Hydroxide (OH–)
Chloride (Cl–)
Peroxide (O22-)
Amide (NH2–)
Fluoride (F–)
Acetate (CH2COO–)
Sulfide (S2-)
Pyridinium (C5H5NH+)
Now let us select a few examples from the above and discuss in detail why is it a polar or a non-polar ion.
A sodium (Na) atom belongs to Group I A (or 1) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p6 3s1.
In order to gain a complete octet electronic configuration, the Na-atom loses its single valence electron and transforms into Na+ ion during chemical bonding.
The Na+ ion thus has a complete octet (1s2 2s2 2p6). All the electrons surrounding the sodium cation are uniformly spread in a spherical arrangement around the nucleus. Hence it is a non-polar cation.
Chloride (Cl–) ion
Chlorine is a halogen present in Group VII A (or 17) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p6 3s2 3p5. The Cl-atom gains 1 electron and obtains a complete octet configuration (1s2 2s2 2p6 3s2 3p6).
The negative charge present on Cl– is not concentrated at a single point. Rather, it is evenly dispersed all over the anion. Thus, it is a non-polar monoatomic anion.
You may note that Na+ and Cl– are individually non-polar ions; however, they rarely exist in the free state and readily form new chemical bonds; for e.g., the ionic bond between Na+ and Cl– in sodium chloride salt.
A specific charge separation exists between the two ions after bond formation, so the resulting ionic bond is always polar in nature.
The concept of polarity has little significance w.r.t monoatomic ions. Rather, it is more relevant to polyatomic ions, as polarity refers to the electron cloud distribution between more than 1 constituent specie.
Examples of non-polar polyatomic ions
Phosphate (PO43-) ion
The phosphate (PO43-) ion comprises a phosphorus (P) atom at the center. Four oxygen (O) atoms surround the central P-atom. 1 O-atom is bonded to the central P-atom via a double-covalent bond, while the other 3 O-atoms are single-covalently bonded.
Phosphorus belongs to group V A (or 15). Its electronic configuration is 1s2 2s2 2p6 3s2 3p3, which implies that it has a total of 5 valence electrons.
A high electronegativity difference of 1.25 units exists between a P-atom (E.N = 2.19) and an O-atom (E.N = 3.44). Therefore, each P-O (or P=O) bond is individually polar, possessing a strong dipole moment value.
However, these P-O dipole moments get canceled equally due to the symmetrical tetrahedral shape of the ion. So PO43- is overall non-polar.
Sulfate (SO42-) ion
The most stable resonance structure of a sulfate (SO42-) ion displays 2 S=O double bonds and 2 S-O single covalent bonds.
Sulfur (S) is present in group VI A (or 16). Its electronic configuration is 1s2 2s2 2p6 3s2 3p4. It has a total of 6 valence electrons.
Each S-O (or S=O) bond is polar as per an electronegativity of 0.86 units between the covalently bonded sulfur (E.N = 2.58) and oxygen (E.N = 3.44) atom.
However, the S-O dipole moments get canceled uniformly in the symmetrical shape of sulfate. So, it is overall a non-polar molecular ion.
Borate (BO33-) ion
Boron is an element from group III A (or 13) of the Periodic Table. It possesses a total of 3 valence electrons, as per an electronic configuration of 1s2 2s2 2p1.
All 3 valence electrons of the central B-atom get consumed in covalent bonding, leading to a symmetrical, trigonal planar shape of BO33-.
The strong dipole moments of three B-O bonds get canceled equally in opposite directions, resulting in an overall non-polar borate (BO33-) ion.
Peroxide (O22-) ion
The peroxide ion comprises two identical oxygen (O) atoms arranged in a linear molecular shape.
Zero or no electronegativity difference exists between the identical O-atoms. The O-O electron cloud stays equally shared between the two oxygen atoms; thus, the peroxide (O22-) ion is overall non- polar.
Examples of polar polyatomic ions
Hydronium (H3O+) ion
Oxygen belongs to group VI A (or 16). Its electronic configuration is 1s2 2s2 2p4.
Out of the 6 valence electrons of an O-atom, only 3 get consumed in covalent bonding in the hydronium (H3O+) ion. The central O-atom also carries a +1 charge.
Hence, there are 2 valence electrons present as a lone pair on the central O-atom in H3O+. This lone pair leads to strong lone pair-bond pair electronic repulsions that distort the overall shape and geometry of the molecular ion.
Each O-H bond is strongly polar as per an electronegativity difference of 1.24 units between the covalently bonded oxygen (E.N = 3.44) and hydrogen (E.N = 2.20) atoms.
The strong O-H dipole moments do not get canceled due to the asymmetrical molecular shape. Consequently, H3O+ is a polar molecular cation (net µ> 0).
Chlorite (ClO2–) ion
As discussed already, a Cl-atom possesses a total of 7 valence electrons. In the ClO2– ion, two O-atoms are covalently bonded to the central Cl-atom by a single and a double-covalent bond, respectively.
3 valence electrons consumed out of the 7 initially available leaves behind 4 valence electrons, i.e., 2 lone pairs on the central Cl-atom.
These 2 lone pairs lead to strong lone pair-lone pair and lone pair-bond pair electronic repulsions. The overall molecular shape gets distorted. The ClO2– ion thus occupies an asymmetrical bent, angular, or V-shape.
Both Cl-O and Cl=O bonds are slightly polar, having an electronegativity difference of 0.28 units between the bonded atoms.
But it is due to the asymmetric, bent shape that the small dipole moments stay uncancelled to yield an overall polar molecular ion with a permanent dipole moment value.
FAQ
Are all ions polar?
No. Ions can be polar or non-polar depending upon the type of ion, constituent atoms involved, and/or symmetry.
Monoatomic ions formed by the loss or gain of electrons by a single atom only are generally non-polar. Examples include Na+, Mg2+, Cl–, O2-, etc.
Polyatomic ions can be polar or non-polar.
For example, SO42- is a non-polar molecular ion as it possesses a symmetrical tetrahedral shape. The dipole moments of individually polar S-O (and S=O) bonds get canceled equally.
Contrarily, SO32- is a polar molecular ion as the individual dipole moments stay uncancelled due to the asymmetrical trigonal pyramidal molecular shape.
Are sodium ions polar?
The sodium (Na+) ion is a cation formed by the loss of 1 electron from the Na-atom. The remaining 10 electrons revolve around the nucleus in a spherical symmetrical manner.
The +1 charge is present on the sphere as a whole (not concentrated at a specific point or location); thus, Na+ is a non-polar ion.
However, the ionic bond it forms with Cl– is polar in nature.
Are all polyatomic ions polar?
Polyatomic or molecular ions comprise two or more atoms covalently bonded together, possessing a net charge.
Polyatomic ions can be polar or non-polar, depending upon the constituent atoms and the molecular shape.
Are carbonate ions polar?
No. The carbonate (CO32-) ion is non-polar.
It consists of a carbon (C) atom surrounded by 3 oxygen (O) atoms, 1 C=O bond, and 2 C-O bonds are present in a symmetrical trigonal planar arrangement.
Each C-O (or C=O) bond is polar, having an electronegativity difference of 0.89 units between the covalently bonded atoms.
However, the net dipole moment effect of two downwards-pointing C-O bonds gets canceled equally with the dipole moment of an upwards-pointing C=O bond.
Yes. The triiodide (I3–) is polar. Although, it consists of three identical iodine (I) atoms having zero or no electronegativity differences in a planar linear arrangement.
In this way, I3– is considered polar and is an exception opposing the general non-polar behavior of polyatomic ions possessing a single type of atom only.
Summary
Ions are charged species formed by the loss or gain of electrons.
Ions can be classified into cations and anions. These can be subdivided into monoatomic, polyatomic, and complex ions.
Monoatomic ions are generally non-polar.
Polyatomic ions can be polar or non-polar depending upon the constituent atoms involved and their molecular arrangement or shape.
Examples of monoatomic ions are Na+, Mg2+, Cl–, etc.
Examples of non-polar polyatomic ions are PO43-, SO42-, NH4+, O2–, etc.
A few examples of polar polyatomic ions are H3O+, OH–, SO32-, ClO2–, etc.
References
OneClass. ‘Are the following polyatomic ions polar or non-polar?’’. https://www.youtube.com/watch?v=uVSIFxzUc_U&t=2s&ab_channel=OneClass
LibreTexts Chemistry. ‘Polarity in Polyatomic Molecules’’. Aug 31st, 2022. https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_ChemPRIME_(Moore_et_al.)/07%3A_Further_Aspects_of_Covalent_Bonding/7.12%3A_Polarity_in_Polyatomic_Molecules
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Borate (BO33-) ion
