What is a Polar Covalent Bond? (With Examples)

A Polar covalent bond Is a covalent bond between two atoms where the electrons forming the bond are unequally distributed.

This causes the molecule to have a slight electrical dipole moment in which one end is slightly positive and the other slightly negative. What is a Polar Covalent Bond?  (With Examples)

The charge of the electric dipoles is less than a complete unit load, so they are considered partial charges and are denoted by delta plus (δ +) and delta minus (δ-) (Boundless, 2016).

Because positive and negative charges separate at the bond, molecules with polar covalent bonds interact with dipoles in other molecules.

This produces dipole-dipole intermolecular forces between them (Helmenstine, Polar Bond Definition and Examples, 2017).

Electronegativity and link polarity

The polarity of a bond (the degree to which it is polar) is largely determined by the relative electronegativities of the bonded atoms.

The Electronegativity (Χ) is defined as the ability of an atom in a molecule or an ion to attract electrons to itself. Therefore, there is a direct correlation between electronegativity and bond polarity (Polar Covalent Bonds, S.F.).

A bond is non-polar if the joined atoms have the same or similar electronegativities. If the electronegativities of the joined atoms are not equal it can be affirmed that the bond is polarized toward the most electronegative atom.

A bond in which the electronegativity of B (χB) is greater than the electronegativity of A (χA), for example, is indicated by the partial negative charge on the most electronegative atom:

TO Δ + -B Δ-

The greater the value of electronegativity, the greater the force of the atom to attract a pair of bonding electrons.

Figure 1 shows the electronegativity values ​​of the different elements under each symbol in the periodic table.

With some exceptions, electronegativities increase from left to right over a period, and decrease, from top to bottom, in a family. (Electronegativity: Classifying Bond Type, S.F.).

What is a Polar Covalent Bond?  (With Examples) 1 Figure 1: Electronegativity values ​​of the elements of the periodic table according to the Pauling convention.

Electronegativities give information about what will happen to the pair of bonding electrons when two atoms join.

Polar covalent bonds are formed when the atoms involved have an electronegativity difference between 0.5 and 1.7.

The atom that attracts the pair of bond electrons most strongly is slightly more negative, while the other atom is slightly more positive by creating a dipole in the molecule.

The greater the difference in the electronegativities, the atoms involved in the bond will be more negative and positive. (ELECTRONEGATIVITY AND POLAR COVALENT BONDING, S.F.).

Polar bonds are the dividing line between the pure covalent bond and the pure ion bond.

Pure covalent bonds (non-polar covalent bonds) share even electron pairs between atoms.

Technically, non-polar bonding occurs only when the atoms are identical to each other (eg, gas H 2 Or gas Cl 2 ), But chemists consider any bond between atoms with a difference in electronegativity of less than 0.4 to be a non-polar covalent bond.

For example, carbon dioxide (CO 2 ) And methane (CH 4 ) Are non-polar molecules.

In ionic bonds, the electrons in the bond are donated essentially to one atom by the other (eg, NaCl).

Ionic bonds are formed between atoms when the difference in electronegativity between them is greater than 1.7. In the case of ionic bonds, there is no electron sharing and the bonding occurs by electrostatic forces.

What is a Polar Covalent Bond?  (With Examples) 2 Figure 2: types of bond (a) non-polar covalent bond, (b) polar covalent bond and (c) ionic bond

Examples of polar covalent bonds

The water (H 2 O) is the most classic example of a polar molecule. It is said that water is the universal solvent, but this does not mean that it dissolves universally, but rather that due to its abundance it is a suitable solvent to dissolve polar substances (Helmenstine, 2017).

According to the values ​​in figure 1, the electronegativity value of oxygen is 3.44, while the electronegativity of the hydrogen is 2.10.

The inequality in the distribution of electrons explains the folded form of the molecule. The"oxygen"side of the molecule has a net negative charge, while the two hydrogen atoms (on the other"side") have a net positive charge (figure 3).

What is a Polar Covalent Bond?  (With Examples) 3 Figure 3: Link polarity of the water molecule.

Hydrogen chloride (HCl) is another example of a molecule having a polar covalent bond.

Chlorine is the most electronegative atom, so the electrons in the bond are more closely associated with the chlorine atom than with the hydrogen atom.

A dipole is formed with the chlorine side having a net negative charge and the hydrogen side having a net positive charge. Hydrogen chloride is a In the linear molecule because there are only two atoms, so no other geometry is possible.

What is a Polar Covalent Bond?  (With Examples) 4 Figure 4: Link polarity of the hydrogen chloride molecule.

The ammonia molecule (NH 3 ) And the amines and amides have polar covalent bonds between the nitrogen, hydrogen and substituent atoms.

In the case of ammonia, the dipole is such that the nitrogen atom is more negatively charged, with the three hydrogen atoms all on one side of the nitrogen atom with a positive charge.

What is a Polar Covalent Bond?  (With Examples) 5 Figure 5: Link polarity of the ammonia molecule.

Asymmetric compounds exhibit polar covalent characteristics. An organic compound with functional groups having electronegativity difference shows polarity.

For example, 1-chlorobutane (CH 3 -CH 2 -CH 2 -CH 2 Cl) shows a partial negative charge on Cl and the partial positive charge distributed over the carbon atoms. This is called inductive effect (TutorVista.com, S.F.).

References

  1. (2016, Aug. 17). Covalent Bonds and Other Bonds and Interactions . Retrieved from boundless.com.
  2. ELECTRONEGATIVITY AND POLAR COVALENT BONDING . (S.F.). Retrieved from dummies.com.
  3. Electronegativity: Classifying Bond Type . (S.F.). Retrieved from chemteam.info.
  4. Helmenstine, A. M. (2017, April 12). Examples of Polar and Nonpolar Molecules . Retrieved from thoughtco.com.
  5. Helmenstine, A.M. (2017, Feb. 17). Polar Bond Definition and Examples . Retrieved from thoughtco.com.
  6. Polar Covalent Bonds . (S.F.). Retrieved from saylordotorg.github.io.


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