Polarization Definition in Physical Chemistry

Polarization

Definition and meaning of Polarization in chemistry.

Polarization is the separation or shifting of electron charge inside a molecule or atom. This unequal sharing of electrons creates distinct areas of partial positive and partial negative charge. This permanent separation of electrical charge is known in chemistry as a dipole moment.

In more detail

In a perfect covalent bond between identical atoms, the atoms share electrons exactly equally. However, different chemical elements pull on shared electrons with completely different physical strengths. Chemists call this measurable pulling strength the electronegativity of an atom.

When two different atoms bond, the more electronegative atom pulls the shared electrons closer to itself. This shifting of negative charge away from the center is called polarization. The greedy atom that pulls harder always gains a partial negative charge.

The weaker atom is left entirely with a partial positive electrical charge. This built-in separation of charge explains why many molecules are polar. This fundamental concept of polarization explains many important chemical behaviors that students study.

It determines whether a solid substance will dissolve easily in liquid water. It also causes vital intermolecular forces like hydrogen bonding to happen. A common student misconception is that only permanently polar molecules can experience polarization.

In reality, even perfectly symmetrical nonpolar molecules can become temporarily polarized in nature. If you place a nonpolar molecule near a strong electric charge, its electron cloud will temporarily distort.

Key facts

Field

Physical Chemistry

Primary cause

Electronegativity differences between bonded atoms

Measured by

Dipole moment

Charge representation

Delta plus and delta minus symbols

Classic examples

Hydrogen chloride, water, ammonia

Temporary effect

Induced polarization in nonpolar molecules

Example

Hydrogen chloride is a classic example of a permanently polarized molecule. A single chemical bond connects one hydrogen atom to one chlorine atom. The element chlorine is significantly more electronegative than the element hydrogen. The chlorine atom pulls the shared bonding electrons forcefully toward its own nucleus. This leaves the hydrogen end of the molecule with a partial positive charge. The chlorine end of the molecule takes on a partial negative charge. This resulting permanent dipole makes hydrogen chloride a highly polar and reactive gas. When this gas dissolves in water, the strong polarization helps it break apart into ions to form hydrochloric acid.

Frequently asked questions

What is the difference between a polar molecule and polarization?

Polarization is the actual physical process of charge separation happening inside a molecule. A polar molecule is simply a molecule that has permanent polarization due to an uneven shape.

Can nonpolar molecules ever become polarized?

Yes. All molecules can be forced to form temporary dipoles if you place them near an external electric field. Chemists call this temporary effect an induced polarization.

How do we show polarization in chemical drawings?

Chemists typically use the lowercase Greek letter delta to represent these partial electrical charges. A delta with a plus sign shows the slightly positive atom. A delta with a minus sign marks the slightly negative atom.