NaCl is the chemical formula for sodium chloride, popularly known as Table salt, which is an essential part of our daily food items.
NaCl (molar mass = 58.44 g/mol) is an ionic compound that exists as a white crystalline solid at r.t.p., possessing an extremely high melting (801° C) and boiling point (1465 °C).
In this article, we have discussed everything you need to know about the polarity of NaCl.
So, to learn whether NaCl is polar or non-polar and the reason behind it, you have to do just one thing, i.e., continue reading this article. Happy learning!
Is NaCl polar or non-polar?
Sodium chloride (NaCl) is polar in nature.
It is an ionic compound composed of oppositely charged sodium (Na+) and chloride (Cl–) ions, tightly held together by strong electrostatic forces of attraction. All ionic compounds are polar in nature.
An extremely high electronegativity difference of 2.23 units exists between a sodium and a chlorine atom. Chlorine (Cl), being strongly electronegative, attracts the Na-Cl electron cloud towards itself to a large extent, away from the electropositive Na-atom.
Due to this unequal electron cloud distribution, the Cl-atom gains a permanent negative charge while the Na-atom obtains a permanent positive charge.
Oppositely charged poles develop in the ionic compound with high dipole moment values.
A large number of oppositely charged Na+ and Cl– ions are held together to produce a strongly polar NaCl crystal lattice (net µ > 0).
A chemical compound is polar if there is a non-uniform charge distribution present in it. If the charge distribution gets equally balanced in different parts, then that molecule or compound is considered non-polar.
The following three factors mainly influence the polarity of a chemical compound:
Electronegativity difference between two dissimilar atoms
Dipole moment
Shape or arrangement of atoms/ions
Now let us discuss the effect of the above three factors one by one to prove that sodium chloride (NaCl) is highly polar.
Factors affecting the polarity of NaCl
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent or ionic bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
Greater the electronegativity difference between bonded atoms in a compound or molecule, the higher the bond polarity.
As per Pauling’s electronegativity scale, a chemical bond formed between two dissimilar atoms is polar covalent if the bonded atoms possess an electronegativity difference between 0.4 to 1.6 units.
Contrarily, if the electronegativity difference between two bonded atoms exceeds 1.6 units, then the nature of bonding changes from covalent to ionic.
An ionic bond is formed by the complete transference of electrons from one atom (usually a metal) to a non-metal atom.
The negatively charged ion (anion) strongly attracts the shared electron cloud away from the positively charged ion (cation), which results in an unequal electronic distribution overall.
In NaCl, there are only two types of elemental atoms, i.e., sodium (Na) and chlorine (Cl).
Na is an alkali metal present in Group I A (or 1) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p6 3s1. As per this electronic configuration, each Na-atom has 1 valence electron. On losing this electron, sodium can achieve a complete octet shell.
In contrast, chlorine is a halogen, situated in Group VII A (or 17) of the Periodic Table. Its electronic configuration is 1s2 2s2 2p6 3s2 3p5, which implies it has a total of 7 valence electrons. Each Cl-atom thus needs one more electron in order to gain a complete octet electronic configuration.
Atom
Electronic configuration
Valence electrons
Sodium (11Na)
1s22s22p63s1
1
Chlorine (17Cl)
1s22s22p23s23p5
7
The Na-atom loses 1 electron and changes to Na+. This electron is gained by a Cl-atom, which is consequently transformed to Cl–.
Strong electrostatic forces of attraction develop between oppositely charged Na+ and Cl– ions to form a Na+ Cl– ionic bond, as shown in the Lewis structure drawn below.
In this way, both sodium and chlorine obtain a completely stable, octet electronic configuration via chemical bonding in NaCl.
A large number of Na+Cl– unit cells are held together to form the NaCl crystal lattice.
In the face-centered cubic (fcc) lattice arrangement, each Na+ ion is surrounded by six Cl– ions and vice versa. Thus, the coordination number of both ions in the NaCl crystal is 6.
An electronegativity difference of 2.23 units exists between sodium (E.N = 0.93) and chlorine (E.N = 3.16). It is greater than 1.6 units; thus, each Na+Cl– bond is a polar ionic bond as per Pauling’s electronegativity scale.
Chlorine being strongly electronegative attracts the Na-Cl shared electron cloud towards itself to a large extent.
Oppositely charged poles develop as each chlorine atom gains a permanent negative charge (Cl–) while each sodium atom obtains a permanent positive charge (Na+), as shown below.
Dipole moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charge separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar chemical bond conventionally points from the positive center to the center of the negative charge.
Hence, in NaCl, the strong dipole moment of each Na+Cl– unit cell points from Na+ to Cl–.
The shape of the ionic compound
As mentioned earlier, NaCl is a face-centered cubic lattice.
In this lattice arrangement, Na+ ions occupy the four corners at the faces of a cube, with one Na+ ion at the center of each face. A negatively charged Cl–ion is present between two oppositely charged Na+ ions on each face.
In this way, the oppositely charged Na+ and Cl– ions are hexagonally arranged w.r.t each other.
The Na+Cl–dipole moments stay uncancelled to yield an overall polar ionic compound, having a resultant dipole moment value as high as 9.001 D.
FAQ
Is NaCl polar? If so, why?
Sodium chloride (NaCl) is polar, as it is an ionic compound, and all ionic compounds are essentially polar in nature.
An electronegativity difference of 2.23 units is present between sodium (E.N = 0.93) and chlorine (E.N = 3.16).
2.23 > 1.6 units, so a chemical bond formed between Na and Cl is purely ionic as per Pauling’s electronegativity scale.
Cl strongly attracts the Na-Cl electron cloud and gains a permanent negative charge, while each Na-atom attains a permanent positive charge.
A large number of Na+Cl– unit cells are held together by strong electrostatic forces of attraction to yield an overall polar salt i.e., NaCl.
Is Table salt polar or non-polar?
Sodium chloride (NaCl) forms the main component of Table salt that we sprinkle on our daily food items.
As NaCl is a polar ionic compound, this means Table salt is also polar in nature.
Why does NaCl dissolve in water?
Like dissolves like. NaCl is a polar salt. It readily dissolves in water (a polar ionic compound) by developing strong dipole-dipole attractions.
When NaCl is added to water, each Na+ ion gets surrounded by six H2O molecules with their partial negative ends (Oδ-) pointing toward positively charged Na+ ions.
Similarly, each Cl– ion gets surrounded by six H2O molecules in a reverse direction. This process is called hydration.
It breaks the strong electrostatic forces of attraction between oppositely charged Na+ and Cl– ions and liberates them to get freely solubilized in water.
Why doesn’t NaCl dissolve in non-polar solvents such as hexane (C6H14)?
Hexane (C6H14) is a non-polar solvent, containing purely non-polar C-C bonds and almost non-polar C-H bonds in the long hydrocarbon chain.
It cannot solubilize polar NaCl as no forces of attraction exist between opposite polarity chemical compounds, and only like dissolves like.
Is MgCl2 more polar than NaCl?
No. In magnesium chloride (MgCl2), each Mg2+ ion is surrounded by 2 Cl– ions. However, it is due to the higher charge (+2) and smaller radius of the magnesium cation that it has a higher polarizing power. Mg2+ can distort the electronic cloud of Cl– ions; therefore, the overall polarity effect reduces.
Also, the electronegativity increases across a Period, so magnesium (E.N = 1.31) is more electronegative than sodium (E.N = 0.93). As the anion is the same in both cases, this implies the electronegativity difference between Mg and Cl (1.85 units) is less than that between Na and Cl (2.23 units).
The lower the electronegativity difference, the less polar the bond formed.
Summary
Sodium chloride (NaCl) is a polar ionic compound.
NaCl consists of oppositely charged Na+ and Cl– ions, held together in a lattice arrangement by strong electrostatic forces of attraction.
An extremely high electronegativity difference of 2.23 units is present between sodium and chlorine.
Each Cl-atom strongly attracts the shared electron cloud away from the Na-atom.
Oppositely charged poles develop as the Cl and Na atoms gain permanent negative and positive charges, respectively.
The Na+Cl– dipole moments stay uncancelled to yield an overall polar ionic compound (net µ > 0).
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