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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.
In an ionic bond, one atom essentially donates 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.
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 Bonds||Covalent Bonds|
|Description||Bond 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.|
|Shape||No definite shape||Definite shape|
|State at Room Temperature||Solid||Liquid or Gas|
|Examples||Sodium chloride (NaCl), Sulfuric Acid (H2SO4 )||Methane (CH4), Hydrochloric acid (HCl)|
|Chemical Species||Metal and nometal (remember hydrogen can act either way)||Two nonmetals|
Do you understand? Test your comprehension with this quiz.
- 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.