Polar Covalent Bond

Polar covalent bond electrons are not equal distance

The electrons are unequally distanced

In a polar covalent bond, no electrons are gained or lost. The electrons position themselves closer to one atom and further away from the other.

The atoms become partially charged

When electrons move closer to an atom, the atom becomes partially negatively charged.  When electrons move further away, the atom becomes partially positively charged.

Polar covalent bonds with partially charged atoms

Electronegativity Bond Scale

The electronegativity bond scale for Polar Bond is between 0.5 to 1.7
Polar Bond Negativity Difference Scale

For more information on Electronegativity Bond Scale

Determine the type of Hydrogen and Chlorine bond using the electronegativity bond scale

Hydrogen and Chlorine Bond

From electronegativity table in Electronegativity by Pauling:
Hydrogen = 2.20
Chlorine = 3.16

Electronegativity between Hydrogen and Chlorine = 3.16 – 2.20 = 0.96

According to the electronegativity bond scale, Polar bonds are between 0.5 to 1.7. So this is a Polar Covalent Bond.

Why hydrogen and oxygen is a Polar Covalent Bond?

The O – H bond ( oxygen to hydrogen)

Polar covalent bond - hydrogen and oxygen

  • The oxygen atom has a bigger electronegativity than the hydrogen atom.
  • It therefore pulls the electrons of the hydrogen atom closer to itself.
  • The oxygen now has more electrons around itself so creating a partially negatively charged oxygen atom.
  • The decrease in electrons around the hydrogen atom creates a partially positively charged hydrogen atom.

That’s how it becomes a polar bond!

Water Molecules

How hydrogen and oxygen are bonded as water molecules

A water molecule with covalent bond
A water molecule with covalent bond
  • The electronegativity difference between oxygen and hydrogen is
  • 3.5 – 2.1 = 1.4
  • The extend of electronegativity difference causes a dipole, meaning the separation of positive and negative charge.
  • The oxygen atom becomes partially negative while the hydrogen atom becomes partially positive.
  • Sometimes you may hear the water molecule being called a bent molecule. The shape is caused by the hydrogen atoms at the tip and oxygen at the vertex.

A water molecule is neutral but the surface has a slight uneven distribution of charges.

Water-elpot-transparent-3D-balls“. Licensed under Public domain via Wikimedia Commons.

A molecule of water is polar. This is caused by the unequal sharing of its electrons in a “bent” structure. A separation of charge is present with negative charge in the middle (red shade – oxygen atom), and positive charge at the ends (blue shade – hydrogen atoms).

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