Ionic vs Covalent Bonds - Understand the Difference

Know the Difference Between an Ionic and Covalent Chemical Bond

Covalent bond
Electrons in a covalent bond are shared equally, while electrons in an ionic bond spend more time closer to one atom than the other. PASIEKA / Getty Images

A molecule or compound is made when two or more atoms form a chemical bond, linking them together. The two types of bonds are ionic bonds and covalent bonds. The distinction between them has to do with how equally the atoms participating in the bond share their electrons.

Ionic Bonds

In an ionic bond, one atom essentially donate an electron to stabilize the other atom. In other words, the electron spends most of its time close to the bonded atom.

 Atoms that participate in an ionic bond have different electronegativity values from each other. A polar bond is formed by the attraction between oppositely-charged ions. For example, sodium and chloride form an ionic bond, to make NaCl, or table salt. You can predict an ionic bond will form when two atoms have different electronegativity values and detect an ionic compound by its properties, including a tendency to dissociate into ions in water.

Covalent Bonds

In a covalent bond, the atoms are bound by shared electrons. In a true covalent bond, the electronegativity values are the same (e.g., H2, O3), although in practice the electronegativity values just need to be close. If the electron is shared equally between the atoms forming a covalent bond, then the bond is said to be nonpolar. Usually, an electron is more attracted to one atom than to another, forming a polar covalent bond. For example, the atoms in water, H2O, are held together by polar covalent bonds.

You can predict a covalent bond will form between two nonmetallic atoms. Also, covalent compounds may dissolve in water, but don't dissociate into ions.

Ionic vs Covalent Bonds Summary

Here's a quick summary of the differences between ionic and covalent bonds, their properties, and how to recognize them:

 Ionic BondsCovalent Bonds
DescriptionBond between metal and nonmetal. The nonmetal attracts the electron, so it's like the metal donates its electron to it.Bond between two nonmetals with similar electronegativities. Atoms share electrons in their outer orbitals.
ShapeNo definite shapeDefinite shape
Melting PointHighLow
Boiling PointHighLow
State at Room TemperatureSolidLiquid or Gas
ExamplesSodium chloride (NaCl), Sulfuric Acid (H2SO4 )Methane (CH4), Hydrochloric acid (HCl)
Chemical SpeciesMetal and nometal (remember hydrogen can act either way)Two nonmetals

Do you understand? Test your comprehension with this quiz.

Key Points

  • The two main types of chemical bonds are ionic and covalent bonds.
  • An ionic bond essentially donates an electron to the other atom participating in the bond, while electrons in a covalent bond are shared equally between the atoms.
  • The only pure covalent bonds occur between identical atoms. Usually there is some polarity (polar covalent bond) in which the electrons are shared, but spend more time with one atom than the other.
  • Ionic bonds form between a metal and a nonmetal. Covalent bonds form between two nonmetals.